· 31 ECIS 2007, 21st Conference of the European Colloid and Interface Society September 10-14, 2007, Geneva, Switzerland Structured surfaces and biointerfaces Contributed lecture

27

ECIS 2007, 21st Conference of the European Colloid and Interface Society

September 10-14, 2007, Geneva, Switzerland

Lecture Abstracts ________________________________________________________________

29



Opening plenary lecture 1

The interaction of highly charged particles or macromolecules

Bo Jönsson*

Theoretical Chemistry, Chemical Centre, POB 124, S-221 00 Lund, Sweden.

Apparently many highly charged (“strongly coupled”) systems are not well described by traditional mean field theory, but have to be approached by more sophisticated methods where ion-ion correlations are taken into account. Mineral systems are good examples of systems that classify as “electrostatically strongly coupled”, which normally means that the surface charge density is high and that divalent counterions are present. Cement paste [1] is a typical example of a cohesive and non-swelling system where ion-ion correlations are important. The salt and pH dependence of early cement cohesion is surprisingly well described by continuum dielectric models provided that ion-ion correlations are included. Initially, when the electrostatic coupling is increased in a system with equally charged particles there is a decrease of the repulsive double layer force, which leads to a situation where an attractive ion-ion correlation force will dominate at short separation. This “initial” attraction can be understood as a classical counterpart to the dispersion force [2]. A further increase of the coupling strength creates a “secondary” repulsion at intermediate separations [3] and an even higher coupling strength will result in an oscillatory force. For oppositely charged particles, the ion-ion correlations will, at intermediate separations, convert the expected attraction into a repulsion, which will be strongly dependent upon the salt concentration, valency and asymmetry in surface charge density of the two particles [4]. Overcharging or charge reversal of particles are common in these systems [5] and the secondary repulsion between equally charged particles as well as the repulsion between oppositely charged particles can be rationalized by introducing an apparent surface charge density. The phenomena are surprisingly accurately described with a correlation-corrected Poisson-Boltzmann theory [6].

A slightly different view on these systems is as a balance between energy and entropy in the dielectric continuum model. In a weakly coupled system entropy will dominate and a net repulsion is found. Vice versa, if entropy is suppressed, like in a system with polyelectrolyte counterions neutralizing the charged particles, energy will dominate and lead to net attractive interactions. This balance can be demonstrated very easily in a one-dimensional model system [1].

Acknowledgment: This work is a collaboration between Univ. de Bourgogne, PMMH ESPCI and Lund University.

1. Jönsson B., Nonat A., Labbez C., Cabane B., Wennerström H., Langmuir, 2005, 21, 9211.

2. Woodward C., Jönsson B., Akesson T. J. Chem. Phys., 1988, 89, 5145. 3. Kekicheff P., Marcelja S., Senden T. J., Shubin V., J. Chem. Phys., 1993, 99, 6098. 4. Trulsson M., Jönsson B., Akesson T., Labbez C., Forsman J., Phys. Rev. Lett., 2006, 97,

68302.5. Pashley R. M., J. Coll. Interface. Sci., 1984, 102, 23. 6. Forsman J., J. Phys. Chem. B, 2004, 108, 9236.

*Corresponding author: Email: [email protected].

30



Structured surfaces and biointerfacesKeynote lecture 1.2

Design of biointerfaces at the micro- and nanoscale:Application to 2D surfaces and 3D objects

Marcus Textor*

BioInterfaceGroup, Laboratory for Surface Science and Technology,Department of Materials, ETH Zürich, Switzerland.

Surface modifications based on biochemical principles are important tools for the fabrication of biosensor chips, biomedical devices such as implants and catheters, and of micron- and nano-scale particles for diagnostic and targeted drug delivery applications.A common ap-proach is eliminating non-specific adsorption rendering surfaces “protein-resistant” or “non-fouling” and adding to such a silent surface biological functionalities such as DNA/RNA, peptides, carbohydrates or proteins/antibodies. Preservation of active conformation and opti-mum presentation of surface-immobilized moieties is a particular challenge to the surface en-gineer in this field. Spontaneous molecular assembly of multifunctional molecules is an at-tractive approach due to its simplicity, cost-effectiveness and compatibility with three-dimensional objects and devices. Molecular assembly systems based on poly(ethylene gly-col)- and poly(methyloxazoline)-grafted polyelectrolytes (PEG- and PMOXA-graft copoly-mers, respectively) will be discussed in the context of controlling the interactiveness of sur-faces with biological media. The factors determining the resistance to non-specific adsorption of PEG- and PMOXA-modified surfaces are discussed in the context of electrostatic and steric-repulsive forces depending on chain density and molecular weight. Schemes for the immobilization of bioligands to protein-resistant surfaces cover covalent coupling, biospecific interactions (biotin/avidin), metal-organic complexation (NTA-Ni-histag) and electrostatic attachment. The corresponding biointerfaces have been quantitatively characterized both exsitu with XPS, ToF-SIMS, and ellipsometry, and in situ using fluorescence microscopy, col-loidal-probe AFM, optical evanescent-field-based sensing and the quartz crystal microbalance (QCM-D) technique. It is also shown how inorganic templates produced by lithography can direct the spatially selective organization of molecules to produce biologically adhesive pat-terns in the micro- and nanometer range in an otherwise non-interactive background.

While higher molecular graft-polyelectrolytes have their merit for the surface modifica-tions of microspheres by self-assembly, nanoparticles require surface-active molecules that are size-wise compatible with the small diameter of such particles. Small biomimetic anchor-age groups derived from mussel-adhesive proteins and cyanobacteria chelates (anachelin) are shown to provide a useful platform for the stable immobilization of PEG and biological func-tionalities to single (oxide) nanoparticles. This is demonstrated for the case of superparamag-netic iron oxide (magnetite) nanoparticles of 20-30 nm diameter, suitable as contrast agent for Magnetic Resonance Imaging (MRI), by stabilization of individual particles with PEG-gallol and biotinylated PEG-dopamine, providing excellent stability of the colloidal solution. A bio-tinylated peptide sequence known to bind specifically to E-selectin was immobilized on the surface of the magnetite particles via streptavidin linkage.


31



Structured surfaces and biointerfacesContributed lecture 1.2.1

Exotic ordered equilibrium structures in binary two-dimensional soft systems

Julia Fornleitner1, Federica LoVerso2, Gerhard Kahl1,*, Christos C. Likos1

1Institut für Theoretische Physik and CMS, TU Wien, Wiedner Hauptstraße 8-10, 1040 Wien, Austria; 2Institut für Theoretische Physik II, Heinrich-Heine Universität Düsseldorf, Universitäatsstraße 1, 40225 Düsseldorf, Germany.

We apply a genetic algorithm technique [1] to predict the ordered equilibrium structures of binary colloidal monolayers. The system that we investigate is a two-component mixture of polystyrene particles, trapped at an oil-water interface [2]. Although already considerable effort has been dedicated in theoretical work to identify the ordered structures of this system, it seems that all these classifications remain incomplete. We demonstrate the power of the genetic algorithm which performs an unbiased search through the parameter space of the possible two-dimensional crystal structures by freely optimising the lattice parameters with respect to the energy. We discover several non-trivial and exotic ordered structures, some of which are hardly accessible to standard methods due to the strong asymmetry and/or the large number of particles per cell. The emergence of individual structures mainly depends on the size and on the particle ratio of the two components. The phononic spectra of the encountered structures are discussed on a preliminary basis. Further, there might be evidence for the existence of stable quasi-periodic structure for this particular system.

1. Gottwald D., Kahl G., Likos C. N., J. Chem. Phys., 2005, 122, 204503-1. 2. Stirner T., Sun J., Langmuir, 2005, 21, 6636.

*Corresponding author: Email: [email protected], Phone 0043 15880113632, Fax: 0043 15880113699.

32



Structured surfaces and biointerfaces Contributed lecture 1.2.2

Mesostructures formation at colloidal monolayers induced by interfacialnon-homogeneities at the air-water interface

J. C. Fernández-Toledano, A. Moncho-Jordá, F. Martínez-López, R. Hidalgo-Álvarez*

Biocolloid and Fluid Physics Group, Department of Applied Physics, Faculty of Science, University of Granada, Granada 18071, Spain.

We study the formation of colloidal mesostructures induced by interfacial non-homogeneities at the air-water interface. The inhomogeneous interface is due to the presence of two liquids with different interfacial tension. The effective potential is assumed to be composed by two terms only, the first is due to the dipolar force (repulsive) between the partly immersed parts of charged microspheres and the second is connected to the interfacial stress caused by the difference in surface tension of both liquids 1 . A potential as simple as this is able to reproduce the experimental mesostructures of colloids confined at the air-water interface found by different authors (see Fig. 1). As a consequence, the mechanism behind the phenomenon of long-range attraction between colloidal particles that are confined at the air-water interface and form mesostructures is not associated to any non-accepted physical interaction but to the formation of an inhomogeneous interface due to the presence in that interface of two liquids with different surface tension 2 .

Fig. 1. Examples of mesostructures (circular clusters and colloidal rings) obtained with the potential of dipolar repulsive force between the charged microspheres and the second connected to the interfacial stress caused by the difference in surface tension of both liquids.

1. Fernández-Toledano J. C., Moncho-Jordá A., Martínez-López F., Hidalgo-Álvarez R., Langmuir, 2006, 22, 6746.

2. Ghezzi F., Earnshaw J. C., J. Phys. Condens. Matter, 1997, 9, L157.

*Corresponding author: Email: [email protected], Phone: 0034 958243213.

33



Structured surfaces and biointerfaces C0302 / Contributed lecture 1.2.3

Interaction of polymeric nanoparticles with cells: Understanding the factors affecting the intracellular localization and cellular processes

Anna Salvati1,2,*, Tiago Santos1,2, Iker Montes1,3, Ian Miller2, William Gallagher2, Yuri Volkov3, Iseult Lynch1, Kenneth Dawson1

1School of Chemistry and Chemical Biology, Belfield, University College Dublin, Dublin 4, Ireland; 2UCD Conway Institute for Biomedical and Biomolecular Research, University College Dublin, Dublin 4, Ireland; 3Institute of Molecular Medicine, Department of Clinical Medicine , Trinity College Dublin, Ireland.

Nanoparticles are widely investigated nowadays for their potential as vectors for drug delivery and diagnostic purposes. However, relatively little is known about the interaction of nanoscale objects with biological systems. Our aim is to try to understand how the cell is affected by the interaction with nanoparticles and what is controlling the final localization of these objects. In a biological fluid, proteins associate with nanoparticles, and we believe that it is the amount and presentation of the proteins on the surface rather than the particles themselves that are the cause of numerous biological responses. It is this outer layer of proteins that is seen by the biological cells, and leads to their responses [1, 2].

To investigate nanoparticle uptake and localisation we are using a set of tailored copolymer nanoparticles that allows us to systematically investigate how the size and composition (hydrophobicity) of the particles affects their interaction with proteins, and thus modulates the cellular response and the eventual intracellular localization. Fluorescently labelled N-isopropylacrylamide (NIPAM): N-tert-butylacrylamide (BAM) copolymer nanoparticles with different co-monomer ratios and fluorescent labels have been solubilised in the presence of serum proteins, and presented to HeLa cells. Confocal microscopy, Flow Cytometry and High Content Analysis have been used for the spatio-temporal visualization of the particles inside the cells, while the new approach of transcriptomics, i.e. the study of mRNA production in response to perturbation, is being applied to define the cell response after the interaction with the biomaterial [3].

1. Lynch I., Dawson K.A., Linse S., Science STKE, 2006, 14. 2. Cedervall T., Lynch I., Lindman S., Berggård T., Thulin E., Nilsson H., Dawson K.A.,

Linse S. PNAS, 2007, 104, 2051. 3. Gallagher W. M., Lynch I., Allen L. A., Miller I., Penney S. C., O’Connor D. P.,

Pennington D., Keenan A. K., Dawson K.A., Biomaterials, 2006, 27, 5871.

*Corresponding author: Email: [email protected], Phone: 0035 317162418, Fax: 0035 317161178.

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Structured surfaces and biointerfacesContributed lecture 1.2.4

Composite nanofiberous thin films for size selective separation of protein

Xinsheng Peng1,2,*, Jian Jin2, Izumi Ichinose2

1International Center for Younger Scientists, National Institute for Materials Science, Japan; 2Nanoorganic Materials Center, National Institute for Materials Science, Japan.

Extremely long and thin nanocomposite fibers were prepared by oxidative polymerization of pyrrole (or aniline) around the surfaces of copper hydroxide nanostrands. The individual nanostrands of 2.5 nm in diameter were uniformly coated with a polypyrrole layer of 3 to 4 nm, giving hybrid core-shell fibers of about 10 nm in diameter and a few micrometers in length, as confirmed by high-resolution electron microscopes. The as-prepared polypyrrole nanofibers were dispersive in water and were able to be converted into the ultrathin free-standing films by simply filtering small volume of the aqueous solution using a polycarbonate membrane filter. The films covering the submicron pores of the membrane filter had a thickness of a few tens of nanometers. They had a uniform network structure with abundant pores of a few nanometers. Because of the chemical and mechanical stabilities of conjugated polymers, the network structure was stable for acids and bases, and the free-standing films were available for protein separation under the pressure at least of 90 kPa. The permeation rates of cytochrome c, myoglobin, and ferritin were examined by changing the pH around their isoelectric points. As a result, it was revealed that the free-standing films on the polycarbonate membranes showed clear size-selectivity for the water-soluble proteins. We demonstrate herein the durable mesoporous separation membranes made of organic/inorganic nanocomposite fibers and their advantages for practical applications.

Fig. 1. (a) SEM images of PPy coated nanostrands, inset TEM image, (b) HRTEM image of PPy coated nanostrands (c) Cross-section SEM image of (a) and its corresponding photograph.

*Corresponding author: Email: [email protected], Phone: 0081 298513354 ext. 8326, Fax: 0081 298527449.

10 nm

100 nm 4 nm 50 nm

(a) (b) (c)

35



Colloidal fluids, crystals and glasses Keynote lecture 1.3

Gelation versus liquid crystal phase transitions in suspensions of charged colloidal platelets

Henk N.W. Lekkerkerker*

Van 't Hoff Laboratory for Physical and Colloid Chemistry, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands.

The liquid crystal phase behaviour of suspensions of charged gibbsite Al(OH)3 platelets is investigated. We study the competition between sedimentation, gelation and liquid crystal formation at different initial concentrations and salt strengths. By variation of the ionic strength we are able to tune the effective thickness-to-diameter ratio of the platelets in suspension. This enabled us to experimentally test the liquid crystal phase transition scenario that was first predicted a decade ago by computer simulations for hard platelets, that is the isotropic (I) nematic (N) and isotropic to columnar (C) phase transitions in one colloidal suspension. In addition to the shape-dependent thermodynamic driving force, the effect of gravity is important. For example a biphasic (I-N) suspension becomes triphasic (I-N-C) on prolonged standing. This effect is described by a simple osmotic compression model. Finally we discuss the possibility to produce photonic crystals from the iridescent columnar phases of Gibbsite nanoparticles.

*Corresponding author: Email: [email protected], Phone: 0031 30253 2547, Fax: 0031 302533870.

36



Colloidal fluids, crystals and glassesContributed lecture 1.3.1

Volume fraction dependence of structural and dynamic properties of charged colloidal dispersions in the low salt regime

Vladimir Lobaskin1,*, Burkhard Dünweg2, Thomas Palberg3,Luis Rojas-Ochoa4, Ramon Castaneda-Priego5

1Biological Soft Matter Theory, Physics Department, Technical University of Munich, Germany; 2Max-Planck-Institute for Polymer Research, Mainz, German; 3PhysicsDepartment, University of Mainz, Germany; 4Physics Department, Cinvestav-IPN, Mexico; 5Institute of Physics, University of Guanajuato, Leon, Mexico.

The structural and dynamic properties of colloidal dispersions in the low-salt regime have been recently attracting much experimental and theoretical attention. Beside the experimental difficulties posed by these systems, a number of intriguing observations have been made that challenge the theories of electrostatic screening and electrokinetics. Some of the conceptual difficulties for theory originate from the counterion dominance in the ionic cloud of the colloid, which makes the screening properties of the background electrolyte dependent on the colloidal concentration. The same is true for the colloidal effective charge or zeta potential that would also change with the concentration as the bulk electrochemical potential of counterions is affected. Therefore, understanding these systems within the usual one-component, colloid only, description is possible solely by using effective density-dependent screening and interaction parameters.

The central goal of this work is to find a systematic way of characterizing the dependence of interparticle interactions and macroscopic properties of colloidal dispersions on the colloid volume fraction. For this purpose we define a set of dimensionless parameters (renormalized particle charge and effective scaled screening length), which enables an universal description of various properties of charged colloids in a wide range of conditions [1-3]. We use our scaling ansatz to analyze static structure and electrokinetic properties of deionized colloidal dispersions as obtained by various experimental techniques and computer simulations [1-4] and produce master curves for their volume fraction dependencies. For the case of monovalent ions, we also propose a simple mean field theory of screening that takes into account the colloidal correlations and predicts accurately the required scaling parameters [2]. We show that our scaling approach applies to conditions of (i) counterion dominated screening that appear, for example, at low salt and finite colloid concentrations, and (ii) screening with a multivalent salt, where the mean field theories are unsuccessful.

1. Lobaskin V., Dünweg B., Medebach M., Palberg T., Holm C., Phys. Rev. Lett., 2007, in press, cond-mat/0601588.

2. Castaneda-Priego R., Rojas-Ochoa L. F., Lobaskin V., Mixteco-Sánchez J. C., Phys. Rev. E, 2006, 74, 051408.

3. Rojas-Ochoa L. F., Castaneda-Priego R., Lobaskin V., Stradner A., Scheffold F., Schurtenberger P., 2007, submitted.

4. Lobaskin V., Dünweg B., Holm C., J. Phys. Cond. Mat., 2004, 16, S4063.


37




Temporal heterogeneity and spatial correlation of the slow dynamics of soft glassy systems

Agnès Duri1,2,*, Luca Cipelletti2, Régine Perzinski3, Aymeric Robert4

1Deutsches Elektronen-Synchrotron (Desy)-Hamburger Synchrotronstrahlungslabor (Haylab), Hamburg, Germany; 2Laboratoire des colloïdes, Verres et Nanomatériaux (LCVN), University of Montpellier II, France; 3Laboratoire Liquides Ioniques & Interfaces chargées, University of Pierre et Marie Currie - ESPCI, France; 4Standford Linear Accelerator Center (SLAC), Standford, USA.

Understanding the dramatic slowing down of the dynamics in systems undergoing a glass transition is one of the key problems in condensed matter and statistical physics. Recent theories and simulations have focussed on the role of dynamical heterogeneity: as the glass transition is approached, the dynamics becomes increasingly correlated in space, since rearrangements are possible through a cooperative motion of “clusters” of particles [1].

We have investigated experimentally the dynamics of two soft glassy materials: a strongly attractive colloidal gel [2] and a concentrated repulsive ferrofluid [3].By applying a novel space- and time-resolved correlation method to the data from the Multispeckle Light Scattering technique, we show that the local dynamics of the colloidal fractal gel is strongly heterogeneous in time suggesting that this system relaxes through discrete rearrangement events. We also find that surprisingly this local dynamics exhibits a long-range spatial correlation which means that each event affects a volume much larger than the size of the clusters. The latter result is in stark contrast with simulations and experiments on supercooled fluids, where the dynamics is found to be spatially correlated on length scales corresponding to a few particles sizes at most.

By applying the time-resolved correlation (without the spatial resolution) method to the data from the X-ray Photon Correlation Spectroscopy technique, we show that the temporal dynamics of the ferrofluid is also heterogeneous. In contrast to the colloidal fractal gel, the independence of the amplitude of the dynamic fluctuations with the length scale probed suggests that there are several independent regions of a few particles where the dynamics is cooperative. In this case, the experimental findings are in agreement with the predictions stipulated by the simulations.

1. Glotzer S. C., J. Non-Cryst Solids, 2000, 274, 342. 2. Cipelletti L., Manley S., Ball R. C., Weitz D. A., Phys. Rev. Lett, 2000, 84, 2275. 3. Meriguet G., Dubois E., Boué F., Cebers A., Farago B., Perzynski R., J. Phys. Chem. B,

2006, 110, 26001.


38




Near wall dynamics of spherical colloids and the influence of a suspension of rods

Peter Holmqvist*, Peter Lang, Jan Dhont

Institut für Festkörperforschung, Teilinstitut Weiche Materie, Forschungzentrum Jülich, 52425, Jülich, Germany.

We have performed dynamic light scattering applying evanescent wave techniques [1] to study the dynamics of spherical colloids close to the solid/liquid interface. The time auto-correlation functions of the scattered intensity (TACF) differ significantly from those measured in the bulk. In the eighties Lan et al. [1] showed that this deviation can in part be explained by the reflection of the particles from the wall. However in the meantime the instrumentation has improved significantly, and with our new experimental design we are able to vary the scattering vector components parallel, Qp, and normal, Qn, to the interface independently. Consequently we can, for the first time, distinguish the contributions to the diffusion coefficient parallel and perpendicular to the interface. In our theoretical derivation of the TACF we also take into account the wall drag effects [2] which make the diffusion coefficient vary with the distance from the interface. With this theoretical approach included into our data analysis we can determine an effective mean diffusivity parallel and normal to the surface of spherical particle. We also investigated the effect of a suspension of rods using monodisperse rods, fd-virus. A clear decrease in the mobility and an increase of anisotropy of the colloidal spheres was observed.

1. Lan K. H., Ostrowsky N., Sornette D., Phys. Rev. Lett., 1986, 57, 17. 2. Feitosa M. I. M., Mesquita O. N., Phys. Rev. A, 1991, 44, 6677.


39




Non-central forces in crystals of charged colloids

Urs Gasser1,*, D. Reinke2, H. Stark3, H.-H. von Grünberg4, A.B. Schofield5, G. Maret1

1Laboratory for Neutron Scattering, ETH Zurich and Paul Scherrer Institut, 5232 Villigen PSI, Switzerland; 2Physics Department, University of Konstanz, 78457 Konstanz, Germany; 3Max-Planck-Institut für Dynamik und Selbstorganisation, Bunsenstr. 10, 37073 Göttingen, Germany; 4Karl-Franzens-Universität, 8010 Graz, Austria; 5School of Physics, University of Edinburgh, Edinburgh, Scotland EH9 3JZ, UK.

The elastic properties of fcc single crystals consisting of charged colloidal particles are determined from snapshots of particle configurations obtained in real-space imaging experiments using confocal microscopy. The normal modes and the force constants of the crystal are extracted from the fluctuations of the particle positions around the lattice sites using the equipartition theorem. All elastic constants of the colloidal crystal are obtained from the long-wavelength limit. We find that the Cauchy relation is not fulfilled and that only non-central many-body forces can account for the elastic properties. The elasticity of the studied crystals is analogous to that of metals in the sense that the small ions in the solvent of the colloidal crystals play a role analogous to that of electrons in metals and give rise to the non-central forces between the big colloidal particles. As in metals, mainly the bulk modulus is affected by the many-body forces. *Corresponding author: Email: [email protected], Phone: 0041 563103229, Fax: 0041 563102939.

40



Highlight topic plenary lecture 2

Polymeric nano-carriers for pulmonary drug and gene delivery

Thomas Kissel*, Christine Oster, Matthias Wittmar, Lea Ann Dailey

Department of Pharmaceutics and Biopharmacy, University of Marburg, Germany.

Gene therapy appears to be a promising approach in the treatment of pulmonary diseases. It aims at either supplementing a defective mutant allele with a functional one or repressing the expression of a pathologically induced transcript. A major challenge in pulmonary and parenteral drug delivery is to design suitable carrier systems for hydrophilic macromolecular drugs, such as oligonucleotides, siRNA or p-DNA. Approaches based upon “intelligent” polymers allowing the preparation of nano-scale objects have recently attracted increasing interest. “Nanomedicine” attempts to understand the biological fate of these carriers. Biodegradable nano-carriers can be generated using a solvent-diffusion technique using novel branched poly[vinyl-3-(dialkylamino)alkylcarbamate-co-vinyl acetate-co-vinyl alcohol]-graft-poly(D,L-lactide-co-glycolide), abbreviated as DEAPA-PVAL-g-PLGA polyesters [1]. Branched polyesters in water-miscible organic solvents allow gentle nano-encapsulation of DNA and proteins based on the Marangoni effect. The feasibility of this approach was studied using a reporter gene expressing Luciferase. The NP compared to naked DNA and polyplexes with poly(ethylenimine), PEI as negative and positive controls showed at N/P ratios 9 a ca. 56x increased transfection efficiency compared to PEI [2]. The potential of biodegradable nano-carriers was also evaluated for pulmonary drug delivery of nano-carriers from DEAPA-PVAL-g-PLGA could be stabilized with carboxy-methyl-cellulose allowing nebulization and manipulation of surface charges. The inflammatory potential was relatively low in acute toxicity studies (mice) and uptake into specific lung tissues could be achieved. These nano-carriers merit further investigations.

Acknowledgement: Financial support of DFG Forschergruppe FOR 627 “Nanohale” is gratefully acknowledged.

Fig. 1. Schematic representation of transfection using DNA nanoparticles.

1. Wittmar M., Kissel T., Macromolecules, 2006, 39, 1417. 2. Oster C. G., Wittmar M., Bakowsky U., Kissel T., J Control Release, 2006, 111, 371.


41



Pharmaceutical applications and drug delivery systems Keynote lecture 2.2

Adhesion, aggregation, flow and diffusion in nanocarrier targeting and drug delivery

Alexander T. Florence*

Centre for Drug Delivery Research, The School of Pharmacy, University of London, London WCN 1AX, United Kingdom.

In spite of many spectacular advances in the development of targeting systems for drug delivery and in the understanding of targets, the translation of results obtained in tissue culture to in vivo success has been limited. A variety of nanocarrier systems have been developed, some like dendrimers with diameters as small as 5nm, offering defined architectures to enable the precise attachment of specific ligands, yet their success to date in achieving anything near quantitative delivery to specific sites is limited. In studying the potential interactions between carriers and receptors at close (nm) approach, we have perhaps neglected the complexity of the route carrier take from point of administration to targets often distant from access to blood supply. As the movement of particles either in capillaries or lymph vessels, their extravasation and diffusion in tissues is size dependent, aggregation or flocculation of particles, their adsorption onto blood components and other colloidal behaviour patterns must be acknowledged. Decorating particles with biological ligands perforce alters physical surface characteristics. Flow of particles even 500nm in diameter can occur in a single file fashion in the mesenteric lymph, so that post-absorptive events such as their aggregation can prevent further translocation. Adhesion of carrier and cell is usually studied in vitro in static conditions while adhesion of ligand-bearing nanoparticles in vivooccurs under varying dynamic conditions. In gene therapy, whose success has been hampered by problems of delivery by safer non-viral vectors, the cell nucleus is the final goal. Diffusion and transport if self-fluorescent dendrimers in cells and uptake into the nucleus has been studied in our laboratory [1,2] and represents, it appears to us, the final barrier to quantitative delivery of nanosystems. The colloidal verities must be taken into account in designing the second generation of targeting systems which will inevitably be a compromise between competing biological and physico-chemical demands

1. Ruenraroengsak P., Al-Jamal K.T., Hartell N., Braeckmans K., de Smedt S. C., Florence A. T., Int. J. Pharm., 2007, 331, 215.

2. Al-Jamal K. T., Ruenraroengsak P., Hartell N., Florence A. T., J. Drug Target., 2006, 14, 405.


42



Pharmaceutical applications and drug delivery systems Contributed lecture 2.2.1

Crystallizable double emulsions for controlled release

Julie Guery1,*, David A. Weitz2, Jérome Bibette3, Wai K. Ng1, Reginald B.H. Tan1

1Institute of Chemical and Engineering Sciences, Crystallisation and Particle Sciences, Singapore; 2Department of Physics, Harvard University, Cambridge, USA; 3Laboratory of Colloidal and Divided Materials, CNRS-UMR 7612, ESPCI, Paris, France.

Efficient encapsulation of active ingredients such as drugs, proteins, vitamins, flavors or nutrients is essential for a myriad of applications from drug delivery to food nutraceuticals and from cosmetics to agrochemicals. Efficient encapsulation demands a robust barrier, while controlled delivery demands an abrupt elimination of this barrier. These competing requirements severely limit the actual available technologies.

In this work, we present a new encapsulating material, a crystallizable double emulsion. This material is made of droplets of water dispersed in larger drops of crystallizable oil, which form a solid shell. We demonstrate that these shells ensure efficient encapsulation but also remain sensitive to an external stress. The application of an osmotic stress between the inner water droplets and the outermost water phase applies sufficient pressure difference to crack the solid barrier, triggering the release of the inner droplets and therefore the encapsulated species. We show that the triggering can be externally controlled either by varying the magnitude of the osmotic stress or by tuning the crystalline nature of the shell which can simply be adjusted by mixing oils with different propensities to crystallize. A crystalline material leads to a material which presents a fast delivery without any breaks of the structure. By contrast, when the solid membrane is amorphous, the delivery is dramatically slowed-down and is accompanied by an important evolution of the structure. It is hypothesized that a crystalline shell can be compared to a brittle material and a more amorphous shell to a plastic or ductile material. X-Ray diffraction and DSC measurements corroborate this hypothesis and give light to the influence of the nature of the shell on the behavior of the material when it is subjected to an osmotic stress.

To conclude, we show that this approach overcomes the competing demand of robust protection and triggered release of encapsulated species, and makes of this material a future candidate for the food, pharmaceutical and personal care industry.

Corresponding author: Email: [email protected], Phone: 0065 67963852, Fax: 0065 63166183.

43




Novel hexyl substituted polylactide micelles as drug carriers for poorly soluble drugs

Karine Mondon*, Robert Gurny, Michael Möller

Department of Pharmaceutics and Biopharmaceutics, School of Pharmaceutical Sciences, University of Geneva, University of Lausanne, Geneva, Switzerland.

Due to their good biodegradability and biocompatibility, polylactides (PLA) are interesting biomaterials for medical and pharmaceutical applications. However PLAs have limited applications for the incorporation of many hydrophobic drugs. To overcome this problem novel hydrophobic PLAs were synthesised by Ring Opening Polymerisation (ROP) from lactide-based monomers functionalised with one or two hexyl groups (PmHLA and PdiHLA, respectively) [1]. These hydrophobic polymers can be copolymerised with the hydrophilic Methoxy Polyethylene Glycol (MPEG) to form block copolymers, which in aqueous conditions self-assemble to micelles [2]. Hydrophobic drugs, that are difficult to formulate due to their low water solubility, can be incorporated into the hydrophobic core. The novel polymeric micelles are prepared by a simple method similar to the nanoprecipitation technique. They have a spherical shape and sizes between 20 and 80 nm with a homogeneous size distribution [Fig.1b]. In very diluted conditions they are stable due to their low critical micellar concentration of 9mg/L. MTT tests on ovarian cancer cells have shown non toxicity. MPEG-hexPLA micelles incorporate more hydrophobic Nile Red, as a fluorescent probe than the standard MPEG-PLA micelles [Fig.1a]. Also the incorporation of different very poorly water soluble drugs was proven. For example, for the incorporation of Cyclosporine A, MPEG-PdiHLA micelles increase the water solubility of the drug by a factor of 55, which is 3.5 times more than for the comparable standard MPEG-PLA micelles. Therefore, these novel hexyl substituted polylactide micelles are promising injectable drug delivery systems for medical treatments with poorly water soluble drugs.

b)

29nm

MPEG-PdiHLA

MPEG-PmHLA

MPEG-PLA

a) H20MPEG

Fig. 1. a) Influence of the hydrophobicity of MPEG-hexPLA micelles on the fluorescence intensity of Nile Red. b) DLS and CryoTEM of unloaded MPEG-PmHLA micelles.

1. Trimaille T., Gurny R., Möller M., Chimia, 2005, 59, 348. 2. Trimaille T., Mondon K., Gurny R., Möller M., Int. J. Pharm., 2006, 319, 147.


44




Kinetics of chiral self-assembly of lipoamino acids into nanotubes

Lior Ziserman, Amram Mor, Dganit Danino*

Department of Biotechnology and Food Engineering, and the Russel Berrie Nanotechnology Institute, Technion, Haifa, 32000 Israel.

Lipo-amino acids belong to a new generation of environmentally friendly surfactants, displaying promising properties such as high surface-activity, low toxicity, and low manufacture cost. These molecules are also interesting from the biological point of view as they display strong antimicrobial activity against a large spectrum of microorganisms. We recently synthesized a library of such molecules based on N acyl lysines (patent protected), and studied their behavior and properties. Here we report on the time-dependent evolution of structures of N -dilauryllysine (DLL), as studied directly, at the nano-scale, by negative-stain and cryogenic - transmission electron microscopy (TEM). DLL undergoes a continuous progression from nanofibers to closed nanotubes (70-100 nm in diameter and many microns in length), through ribbon elements. Our experiments confirm, for the first time, the coexistence of helical and twisted ribbons, independent of the initial conditions, and suggest that twisted ribbons might be precursors of helically-coiled ribbons. We also show that fusion of twisted ribbons and/or coiled ribbons is the mechanism of nanotubes formation in our system. A model we developed to explain the observed nanostructures and transitions, indicates on hydrophobic interactions and hydrogen bonds as the main forces dictating the chiral self-assembly of our system.

Fig. 1. Cryo-TEM image showing coexistence of twisted ribbons, coiled ribbons, and nanotubes in 3 mM aqueous solution of DLL. The upper black arrow in the main image marks a fusion point of a twisted ribbon (T) and a helically coiled ribbon (C) with a nanotube (N). A magnified image of this fusion point is presented on the right. Black arrows in the magnified image mark the edge of the coiled ribbon. White arrows in the main image show the fusion of helically coiled and twisted ribbons into wider coiled ribbon. Lower black arrow in this image marks a fusion point between two twisted ribbons. S- support film, F- frost on the sample. Bar = 200 nm in the main image and 100 nm in the right panel.


45




A novel technique for nanosensor delivery through cellular membranes

Karen Fisher1,2, Rhodri Jones2, Jonathan W. Aylott2 , Vesselin N. Paunov1,*

1Department of Chemistry, University of Hull, Hull, HU6 7RX, UK; 2Centre for Analytical Bioscience and Department of Immunology, University of Nottingham, NG7 2RD, Nottingham, UK.

We report a new method for delivery of nanosensors through the membrane of living cells. The method is based on using cationic liposomes as encapsulating agents for nanosensors as their membranes naturally fuse with cellular membrane. This makes them prospective vehicles for intracellular delivery of nanosensor probes. Polyacrylamide nanosensor particles were prepared by water-in-oil microemulsion polymerisation where the monomers (acrylamide and N,N-methylene bisacrylamide) and fluorophores are dissolved in water and introduced to the microemulsion as the aqueous phase. The produced nanosensors are spherical polymeric particles with a typical diameter of 50 nm which results in sub-second response times, indeed some sensors respond in the millisecond timeframe. Nanosensors consist of a stimulus-responsive fluorescent probe encapsulated into a porous nanoparticle where the fluorophore and other components of the sensor cannot leak out and contaminate the cell interior, while the signal triggering component (analyte) can freely diffuse through the pores of the nanosensor matrix. Using this versatile methodology a range of pH and oxygen sensitive fluorophores were physically entrapped within the nanoparticles polymeric matrix by binding to high molecular weight dextran molecules. We used the lipid extrusion technique to encapsulate our nanosensor particles within the small liposomes doped with a cationic lipid. The nanosensor suspension was mixed with the cationic liposomes followed by multiple extrusions through a polycarbonate membrane. We used TEM to study the degree of encapsulation of the nanosensors inside the liposomes. We used human mesenchymal stem cells (hMSC) to test the nanosensor delivery method by exposing the cells to liposomes modified with fluorescently tagged lipids and cationic liposomes loaded with fluorescently labeled nanosensors. An increase in fluorescence of hMSC was seen following incubation with PC:PG:FITC DHPE liposomes. The hMSC appeared healthy with an increase in size seen after addition of liposomes. We also showed that the nanosensors are successfully delivered into the cell interior after incubation of the hMSC cells with nanosensor loaded liposomes which was confirmed by confocal fluorescence microscopy and other techniques. The developed new method for non-invasive intracellular delivery of nanosensors can find a number of applications for monitoring of the local conditions inside cells for a number of cell types and nanosensors. Intracellular delivery of the nanosensors allowed important metabolic markers (glucose, oxygen, calcium and pH) to be determined as differentiation occurs. This information can help to identify differentiation events and trigger the development of new classes of nanosensors to monitor and record the lineage commitments of hMSC.


46



Nucleation, growth, and organization of colloids Keynote lecture 2.3

Precursor structures in crystallization/precipitation processes and control of particle formation by polyelectrolytes

Jens Rieger*

BASF Aktiengesellschaft, Polymer Physics, Ludwigshafen, Germany.

Crystallization of inorganic (and organic) matter often proceeds via intermediate stages – rather than by simple nucleation and growth mechanisms [1]. These precursor stages not only comprise crystal modifications that are less stable than the final one (Ostwald’s rule of stages), but also amorphous, hydrated (nano-) particles and emulsion-like precursors have been observed [2]. These precursors tend to aggregate or restructure before being dissolved and entering the next structural stage. Structural information on all these intermediates – and by which mechanisms they form – is essential for the understanding of biomineralization and for the development of additives to control crystallization processes.

Our state of knowledge with respect to precursor structures that occur in inorganic particle formation processes from the aqueous phase is outlined. Emphasis is put on how to obtain time-resolved data by combining microscopic and scattering methods. Most of the studies presented focus on the reaction of calcium and carbonate in water and the mode of action that polycarboxylates play during the formation of calcium carbonate precursors and crystals. Recent data on the structural evolution of precipitating CaCO3 obtained by means of X-ray microscopy and quench cryo-transmission electron microscopy will be presented, again emphasizing that the respective particle formation processes do not follow classical nucleation and growth mechanisms [3,4].

Since charged polymers, like polycarboxylates, not only interact with the inorganic precursors and crystals but also with the cations right from the beginning of the precipitation/crystallization reaction it is essential to understand the details of this interaction. Recent time-resolved ATR FTIR studies and molecular modeling experiments on the complexation mechanisms of calcium to polycarboxylates (including all the water molecules) unravel an unexpected richness in the binding process – concerning binding states and their time evolution [5,6].

1. Horn D., Rieger J., Angew. Chem. Int. Ed. 2001, 40, 4330. 2. Haberkorn H., Franke D., Frechen T., Goesele W., Rieger J., J. Coll. Interf. Sci. 2003,

259, 112. 3. Rieger J., Frechen T., Cox G., Heckmann W., Schmidt C., Thieme T., Faraday Disc. 2007,

in press. 4. Niederberger M., Cölfen H., Phys. Chem. Chem. Phys. 2006, 8, 3271. 5. Fantinel F., Rieger J., Molnar F., Hübler P., Langmuir 2004, 20, 2539. 6. Molnar F., Rieger J., Langmuir 2005, 21, 786.


47



Nucleation, growth, and organization of colloids Contributed lecture 2.3.1

Nucleation, growth and superlattice formation of gold nanoparticles probed by time resolved synchrotron SAXS

Olivier Spalla1,*, Benjamin Abecassis1, Fabienne Testard1, Philippe Barboux2

1CEA Saclay, DRECAM/SCM Laboratoire sur l’Organisation Nanométrique et Supramolécu-laire, 91191 Gif sur Yvette France, 2ENSCP, LCAES UMR 7574, 75005, Paris, France.

The main goal of this work is to show that strongly supported conclusions can nowadays be drawn in the field of nucleation and growth of nanomaterials from the use of 3rd generation synchrotron beam lines. Recently, many routes to synthesize nanoparticles became available. On the contrary, the theoretical understanding of the formation of nanoparticles is far from being complete. Indeed, the probing of these phenomena is very challenging due to the short time scale (typically below a second) at which they occur. The availability of the high brilliance synchrotron beams allows in situ Small Angle X-ray Scattering (SAXS) with a sub-second time resolution and a size sensitivity exactly relevant for nanomaterials (going from 0.5 nm to 1 m). Using a fast mixing stopped-flow device, we have studied1 the formation of gold nanoparticles in homogenous phase2, with a combination of experimental techniques (UV, SAXS and WAXS (ESRF, ID02)) at a quantitative level. These experiments (fig.1) and the subsequent data treatment that includes, for the first time, a full fitting at the absolute scale of the SAXS diagrams give a direct access to the number density and size distribution of nuclei and growing nanoparticles during their formation with an unprecedented time resolution (around 100 ms). The results and their fitting strongly support the conclusion that the ligand influences the gold nanoparticles size by controlling their nucleation rate. Two ligands exhibit drastically different behaviours. When an alkanoic acid is used a nucleation phase of 1 s is followed by a growth step whose rate is limited by the reaction of the monomers at the interface. At the opposite, when an alkylamine is used, the nucleation rate is increased by an order of magnitude, thus annealing growth by lack of monomer and yielding R = 1 nm particles in 2 second as compared to R = 3.7 nm in 12 s in the acid case.

Fig. 1. Parallel time resolved UV/SAXS/WAXS probing of the gold nanoparticles formation

1. B. Abécassis, Suivi in situ de la nucléation-croissance de nanoparticules d’or, PhD Thesis, Ecole Polytechnique, Nov 2007.

2. Jana N., Peng X., J. Am. Chem. Soc., 2003, 125, 14280.


48




Assembling colloids with controlled tacticity

Djamal Zerrouki*, Jean Baudry, Jerome Bibette

Laboratoire Colloïdes et Matériaux Divisés, ESPCI, CNRS, UPMC, Paris, France.

We have designed a new type of magnetic colloids that can self-assemble into chains with controlled tacticity. Depending on the shape of the colloidal blocks and their spontaneous direction of magnetization, these colloidal monomers mimic throughout assembling under field angular constraints of atomic covalent binding. As a proof of concept we present self-assembled chains which possess bonds angles of 180° linear (Fig. 1a), 60° in plane (Fig 1b), and 90° out-of-plane (Fig 1c).

a

b

c

Fig. 1. Different examples of chains; with diffierntes monomers, a: homogeneous sphere,bjanus particles ,c: doublet (optical microscopy, scale bar = 1µm).


49




Dynamic control of diffraction within colloidal crystals

D. R. E. Snoswell1,*, C. L. Bower2, P. Ivanov3, M. J. Cryan3, J. G. Rarity3, B. Vincent1

1Physical and Theoretical Chemistry, University of Bristol, Bristol, UK, BS8 1TS; 2KodakEuropean Research, 332 Science Park, Milton Road, Cambridge, UK, CB4 0WN; 3Centre for Communication Research, Dept. of Electrical and Electronic Engineering, University of Bristol, Bristol, UK, BS8 1UB.

The construction of photonic crystals is of interest in a range of applications including lasers, optical circuits, optical fibres, lenses and display devices. A key parameter of colloidal photonic crystals is the particle spacing which influences the optical properties. Typically particle spacing is determined by the diameter of the close packed, monodispersed spheres, and remains fixed once the crystal structure has formed. Here we show the dynamic, reversible control of both particle spacing within two dimensional crystals and three dimensional photonic crystals. Latex particles in aqueous suspension are controlled by an electric field. Because the particles are charged, electrostatic forces prevent the surfaces from touching. However, they are held in crystal structures by temporary dipoles induced by the electric field. As a consequence, changes in field intensity and direction cause rapid and reversible changes in lattice spacing of the crystals, enabling diffraction of white light to be controlled to produce variable visible colours. This technology is the subject of a patent application by Kodak Ltd, and may form the basis of ‘next generation’ display technology.

Fig. 1. Video frames of crystals formed in a rotating electric field (frequency 1000 Hz) when a) no electric field is applied. b) electric field of strength 20 kVrms m-1. c) electric field of strength 81 kVrms m-1. Scale bar represents 10 microns.

a b c

1. Snoswell D. R. E. et al., New J. Phys., 2006, 8, 267.


50




Lead magnesium niobate inks for direct write assembly of 3D periodic structures

Aylin M.Deliormanlı1,*, Erdal Çelik2, Mehmet Polat1

1Izmir Institute of Technology Chemical Engineering Department, Urla, Izmir, Turkey; 2Dokuz Eylul University, Metallurgy and Materials Engineering Department, Izmir, Turkey.

The ability to pattern materials in three-dimensions is critical for several technologies. These structures may find applications in tissue engineering scaffolds, microfluidic networks, sensors, actuators and other electronic ceramic applications [1-3]. Some of these applications require use of functional materials such as relaxor ferroelectrics. Lead magnesium niobate (PMN) is a typical relaxor ferroelectric material with high dielectric constant and excellent electrostrictive coefficient [4].

In this study concentrated PMN inks were designed for direct-write assembly based on attractive and repulsive particle interactions. Three dimensional periodic structures were fabricated using robotic deposition process which is an extrusion based direct write technique [1].

Stable colloidal suspensions (55 vol%) were produced by adding 1 wt% poly (acrylic acid) in terms of the dry weight basis of the PMN powder. Gelation obtained using three different methods. In the first method coagulated inks were prepared by adding poly( ethyleneimine) to the system [5]. It is a highly branched polyamine that contains primary, secondary, and tertiary amine groups in a ~1:2:1 ratio. In the second approach the pH of the system was reduced below pH 9 to obtain a strong gel network. In the last method monovalent and divalent salts were introduced to the system and their ability to construct a gel network was evaluated. Rheological measurements were performed to characterize the gelation behaviour of concentrated suspensions and to optimize the viscoelastic properties. Results showed that divalent salt addition such as zinc acetate or magnesium chloride caused gelation by bridging flocculation, whereas monovalent salt addition just increased the ionic strength and did not increase the viscosity. Periodic lattices having 100 to 500 µm rod size with square and radial geometry were successfully assembled using a robotic deposition apparatus.

1. Lewis A. J., Curr. Opinion Solid State Materials Sci., 2002, 6, 245. 2. Gratson G. M., Lewis A. J, Langmuir, 2005, 21, 457. 3. Smay E. J., Gratson G. M., Shepherd R. F., Cesarano III J., Lewis A. J., Adv. Mater.,

2002, 14, No. 18. 4. Su, F. A.-W. Mater. Chem. Phys., 2000, 62, 18. 5. Nadkarni S. S, Smay E. J., J. Am. Ceram. Soc., 2006, 89, 96.

*Corresponding Author: E-mail: [email protected], Phone: 0090 2327506697, Fax: 0090 2327506645.

51



Self-assembly processes and nanocomposites Keynote lecture 3.2

Ghost-peaks, aligning, and twinning: Ordering in self-assembled soft materials

Andreas Frömsdorf1, Carsten Schellbach1, Andreas Timmann1, Stephan V. Roth2,Peter Lindner3, Stephan Förster1,*

1Department of Physical Chemistry, University of Hamburg, Germany, 2HASYLAB/DESY,Hamburg, Germany, 3Institut-Laue-Langvin, Grenoble, France.

Quasi-forbidden Bragg peaks are frequently observed in such ubiquitous, but seemingly unrelated materials such as lyotropic liquid crystalline phases, mesoporous materials, colloidal dispersions, block copolymers, electrorheological fluids, and photonic crystals. We show that these peaks are an inherent feature of soft materials and solid-state materials prepared therefrom. The peaks arise from a limited coherence of soft lattices.

The development of translational and orientational order and the appearance of quasi-forbidden Bragg-peaks are investigated in-situ using Rheo-SANS experiments on lyotropic liquid crystalline block copolymer solutions. We observe a two-state ordering process where with increasing shear rates first individual domains orient and then grow into two macroscopically phase-separated twins. A mechanism for twin formation analogous to the mechanical twin-formation in plastically deformed metals is proposed. The detailed structure of aligned samples is further investigated by rotating single crystal synchrotron x-ray diffraction and high-resolution scanning electron microscopy. All diffraction patterns can be quantitatively reproduced assuming a mosaic-type crystal structure.

Fig. 1. Diffraction patterns obtained by passing the neutron beam at different directions through the shear cell. The crystalline orientations are indicated by their Miller indices.


Topic: 3) Self-assembly

52



Self-assembly processes and nanocomposites Contributed lecture 3.2.1

Self-assembly of designer peptide block copolymers with charged blocks

Aernout A. Martens1,2,*, Y.Yan2, M.W.T. Werten1, G. Eggink1,M.A. Cohen Stuart2, F.A. de Wolf1

1Bioconversion, Bio based products, A&F, Wageningen University and Research Centre, The Netherlands; 2Laboratory of Physical Chemistry and Colloid Science, ATV, Wageningen University and Research Centre, The Netherlands.

Highly defined polymers are essential for controlled assembly into nano-sized objects and materials for high value applications in (bio) nanotechnology, medicine, tissue engineering, drug delivery, coatings, sensors etc[1]. We exploit the natural protein production machinery of the yeast, Pichia pastoris, for production of designed, monodisperse, sequential polymers from chiral monomers. With 21 different natural monomers (amino acids), physical, chemical and biological functions as well as form and structure can be designed and coded for in DNA and expressed in the host organism. We focus on structure formation, using several driving forces for self assembly: electrostatic interaction, hydrogen bonding and hydrophobic interaction. We produced four (peptide) triblock copolymers consisting of charged, self-assembling silk-like blocks[2] and uncharged hydrophilic random coil blocks[3] which stabilise the formed nanostructures in solution. The silk-like block can be switched from a hydrophilic extended structure to a hydrophobic ß-sheet and back using pH or counter charges. Ultimately these molecules form highly defined tapes, fibrils and gels.

a b

Fig. 1. a) AFM image of self assembled fibrils from a BAB block copolymer with B: a negatively charged self assembling silk like block and A: a hydrophilic random coil. b) cartoon of the same BAB block copolymer switching conformation under influence of charge.

1. Harrington D. A. et al. J. Biomed. Mater. A, 2006, 78A, 157. 2. Krejchi, M.T. et al. Science, 1994, 265, 1427. 3. Werten, M.W.T. et al. Protein Eng., 2001, 14, 447.


53




Preparation of silica with dual meso-/macro- porosity, in highly concentrated emulsions, by a single-step method

J. Esquena*, J. Nestor, C. Solans

Departament de Tecnologia de Tensioactius, Institut d’Investigacions Químiques i Ambientals de Barcelona (IIQAB). CSIC. Jordi Girona 18-26, 08034 Barcelona, Spain.

Highly concentrated emulsions possess volume fractions of the dispersed phase higher than 0.74, the maximum packing of monodispersed spherical droplets [1]. These emulsions have a foam-like structure that consists of deformed and/or polydisperse drops, separated each other by a thin film of continuous phase [1-3], which can possess a nanostructure (e.g. microemulsion or liquid crystal) [2-3]. Their nanostructure is very appropriate for templating because dual meso/macroporous materials can be obtained by polymerizing in the emulsion continuous phase. These dual materials have high specific surface, due to the presence of mesopores, and good permeability because of connected macropores [3-5]. In our first studies, materials with dual meso/macroporous structures were obtained, in a two-step process. In the first step, macroporous polymer foams were prepared by polymerizing in the continuous phase of W/O highly concentrated emulsions [6]. The second step consisted in impregnating the macroporous foams with inorganic precursor solutions containing block copolymer surfactants to form the mesopores. In the work presented here, silica materials with dual meso/macroporous structures were obtained, in simple single-step processes, by polymerizing silica precursors in the continuous phase of O/W highly concentrated emulsions where the continuous phase consisted of supramolecular surfactant aggregates. The results show that meso/macroporous silica and high specific surface areas can be simply obtained.

MacroporesMesopores

Fig. 1. TEM image (left), scheme (center) and SEM image (right) of a meso/macroporous dual material.

1. Lissant K. L., J. Colloid Interface Sci., 1966, 22, 462. 2. Uddin H., Kunieda H., in Structure-Performance Relationships in Surfactants, Esuni K.,

Ueno M., Eds., Surfactant Sciences Series, 112, Marcel Dekker, New York, 2003. 3. Solans C., Esquena J., Azemar N., Curr. Opinion Colloid Interface Sci. 203, 8, 156. 4. Soler-Ilia G. J., Crepaldi E. L., Grosso D., Sanchez C., Curr. Opinion Colloid Interface

Sci., 2003, 8, 109. 5. Esquena J., Solans C., in Emulsions and Emulsion Stability, Sjöblom J., Ed., Taylor and

Francis, New York, 2006. 6. Esquena J., Sankar G. S. R. R., Solans C., Langmuir 2003, 19, 2983.

*Corresponding author: Email: [email protected], Phone: 0034 934006100, Fax: 0034932045904.

54




Blastulae vesicles: Spontaneous formation of catanionic superstructures

Nina Vlachy1,*, Audrey Renoncourt1, Didier Touraud1,Jean-Marc Verbavatz2, Werner Kunz1

1Institute of Physical and Theoretical Chemistry, University of Regensburg, 93040 Regensburg, Germany, 2DBCM/SBCe, C.E. de Saclay, 91191 Gif sur Yvette, France.

Catanionic vesicles of simple surfactant systems (SDS/DTAB) with an overall negative charge can strongly associate at low ionic strength. The result is a highly symmetrical raspberry-like structure, which we named blastulae vesicle, due to its resemblance to the type of embryonic morphology. The series of different morphologies are induced by sodium chloride addition, without any other additives. Aggregation of vesicles without accompanying deformation of membrane had until now only been observed in the systems to which specific ligands and receptors were added. The lack of deformation is due to the fact that not the whole vesicle surface is involved in the interaction, but rather a discrete number of contact points on each surface. In catanionic systems the presence of both charges in the membrane allows for a similar behavior. A redistribution of charges may take place as the cations from the added salt approach the vesicle membrane. At short enough distances, the positive charges of one vesicle can interact favorably with the negative charges of another vesicle and vice versa. The local Coulomb attraction may be strong enough to overcome the overall repulsive force of equally charged vesicles acting at larger distances. Since vesicles are spontaneously formed from lamellar sheets, they are, at this starting point, in close enough contact for this to happen. In this case only localized parts of the membrane (patches) are interacting, similarly to the aforementioned specific site binding and therefore, the membranes are not deformed.

Based on previous studies of biological systems it seems that, despite the simplicity in composition, these assemblies have a potential to mimic the appearance of complex patterns, such as the common state of development of multilamellar organisms.


55




Incomplete lipid chain freezing of sonicated vesicular dispersions of double-tailed ionic surfactants

Pieter Saveyn1,*, Jan Cocquyt1, Torbjörn Drakenberg2, Gerd Olofsson3,Ulf Olsson3, Paul Van der Meeren1

1Particle and Interfacial Technology Group, Faculty of Bioscience Engineering, Ghent University, Belgium; 2Biophysical Chemistry, Center for Chemistry and Chemical Engineering, Lund University, Sweden; 3Physical Chemistry 1, Center for Chemistry and Chemical Engineering, Lund University, Sweden.

Studies on sonicated DODAB[1-3] and DODAC[4] dispersions pointed out that after sonication above the main transition temperature (Tm), part of the lipids remain in the fluid state even when cooled to temperatures far below Tm. However, this incomplete chain freezing phenomenon is not yet fully understood and different explanations have been suggested.

The lipid freezing in dilute sonicated vesicular dispersions was studied using DSC and 1H-NMR. For charged, anionic or cationic, lipids approximately half of the lipids remain in a fluid state when cooled 20 °C below Tm. With a zwitterionic phospholipid, on the other hand, essentially no supercooling of the liquid state was observed. The observations are analysed in terms of the nucleation and growth of flat solid domains in originally fluid spherical vesicles. As the solid domains grow, the remaining fluid domain is deformed resulting in a curvature stress. Depending on the vesicle size and the bilayer bending rigidity, the solid domain growth may terminate as the gain in cohesive free energy is balanced by the curvature stress of the remaining fluid domain. It is argued that high bending rigidities are required for having a significant supercooling, which is why it is only observed for charged lipids. The behavior of flat bilayer fragments was also considered since this is often argued to be the structure which causes incomplete lipid chain melting.

Fig. 1. Schematic representation of the freezing process of a small vesicle with one or two nucleation i

1. Cocquyt J., Olsson U., Olofsson G., Van der Meeren P., Langmuir, 2004, 20, 3906. 2. Brito R. O., Marques E. F., Chem. Phys. Lipids, 2005, 137, 18. 3. Cocquyt J., Olsson U., Olofsson G., Van der Meeren, Prog. Colloid Polym. Sci. 2005,

283, 1376. 4. Lan L., Pansu R., Roncin J., Faure J., Arai T., Tokumaru K., J. Colloid Interf. Sci. 1992,

148, 118.


56



Interfaces and specific ion effects Keynote lecture 3.3

Ion specificity in bulk electrolytes and at interfaces:Ionic adsorption measurements and continuous vs discrete solvent description

Luc Belloni*, Yulia Chikina, Viswanath Padmanabhan, Luc Girard, Jean Daillant

LIONS, Service de Chimie Moléculaire, CEA/SACLAY, France.

Ion specificity comprises all ionic effects which cannot be explained by the genericcoulombic interactions only and where a different behaviour is observed for ions of the same valency (Na+ vs K+, Br- vs Cl-). Its general understanding based on sound physical concepts requires the measurement of ionic distributions at various interfaces with sub-nm resolution and a refined theoretical description of short range multipolar interactions which accounts for dispersion forces and intrinsic ionic polarisability [1]. Grazing incidence x-ray fluorescence was used at the ESRF to precisely quantify the adsorption of ions at the air-water interface of different salt solutions. Small differences in concentration of ions over a few Å could be resolved. X-ray standing waves experiments at the silica-aqueous solution interface reached the same resolution. A primitive model of electrolytes with continuous solvent description succeeded in quantitatively explaining the data for various salt mixtures once a short-range attraction of a few kT for halides was added to coulombic and van der waals forces. This illustrates the merits and limits of a continuous solvent description [2]. In a second level of sophistication, using the standard numerical procedure [3], the molecular HNC integral equation was solved for electrolytes with an explicit description of the water molecules and the polarized ions. Preliminary results for bulk and interfacial systems are compared to previous experimental data, primitive model theories and recent numerical simulations [4].

1. Ninham B., Yaminsky V., Langmuir, 1997, 13, 2097. 2. Kunz W., Belloni L., Bernard O., Ninham B., J. Phys. Chem. B, 2004, 108, 2398. 3. Fries P.H., Patey G.N., J. Chem. Phys., 1985, 82, 429. 4. Jungwirth P., Tobias D., J. Phys. Chem. B, 2002, 106, 6361.


57



Interfaces and specific ion effects Contributed lecture 3.3.1

The “neutral anion” in the Hofmeister series: Dependence on the interface

Epameinondas Leontidis*, Andria Aroti

Department of Chemistry, University of Cyprus, PO Box 20537, 1678 Nicosia, Cyprus

The Hofmeister series of anions plays an important role in a broad range of physicochemical and biological phenomena. Since the original investigations of the effects of electrolytes on protein solubility there have been many attempts to understand the mechanism of specific salt effects, but no consensus exists today on their origin. We have recently used lipid monolayers of DPPC as model systems to understand specific salt effects on soft interfaces [1]. This work is extended here with monolayers of phosphatidylethanolamine lipids (DMPE), which appear to interact more strongly with sodium (the cation of the salts used in this investigation). In contrast to DPPC monolayers, for which NaCl was found to be a “neutral salt”, or salt with minimal influence on the surface pressure, DMPE interacts more strongly with sodium , hence the neutral salt at this interface lies on the right of NaNO3 in the Hofmeister series. Theoretical modeling of the electrical contribution to the surface pressure of the monolayers also implies that the binding of sodium to DMPE interfaces is stronger and must be taken into account to fit the experimental isotherms. The present results indicate how the choice of cation may affect the interfacial behavior of electrolytes and serve to remind that Hofmeister series of anions depend on the cation of the electrolyte as well.

1. Aroti A., Leontidis E., Maltseva E., Brezesinski G., J. Phys. Chem. B, 2004, 108, 15238.

* Corresponding author: Email: [email protected], Phone: 00357 22892767, Fax: 00357 22892801.

58




Ion-specific bubble coalescence inhibition in single and mixed electrolytes

Christine L. Henry*, Vincent S.J. Craig

Department of Applied Mathematics, Research School of Physical Sciences and Engineering, Australian National University, Australia.

Ion specificity is at the heart of many biological processes and is important in all soft matter systems at high electrolyte concentrations, under which conditions the double layer interaction is screened and short-range forces determine colloidal behaviour. Consequently interactions become considerably more complex and the precise character (charge, size, polarizability etc.) and pairing of ions is important. It remains a great challenge for colloid scientists to develop a detailed understanding of ion-specificity.

A simple system that reveals such complex behaviour is that of gas bubbles in salty water. For one hundred years it has been recognized that some electrolytes at sufficiently high concentrations can inhibit bubble coalescence relative to the pure liquid. Electrolytes inhibit coalescence or have no effect as predicted by ion combining rules based on empirical cation and anion assignments.[1] The mechanism behind electrolyte inhibition, as well as the salt differentiation, is not understood. I here report a considerable volume of work on measurements of surface tension and bubble coalescence in aqueous solutions of both single electrolytes and electrolyte mixtures. This has enabled us to rule out surface tension effects as the mechanism of bubble coalescence inhibition.

Recent work shows that some ions show an affinity for the air-water interface while others preferentially inhabit the subsurface[2], and Marcelja has hypothesised that electrolyte effects on coalescence depend upon ion position and separation within the interfacial region.[3] Our mixed electrolyte results are consistent with this hypothesis. I explore mechanisms by which the organization of molecules at the interface can control film rupture at separations of tens of nanometers. We have further extended our investigation to electrolyte effects on bubble coalescence in non-aqueous solvents.

1. Craig V. S. J., Ninham B. W., Pashley R. M., Nature, 1993, 364, 317. 2. Jungwirth P., Tobias D. J., Chem. Rev., 2006, 106, 1259. 3. Marcelja S., J. Phys. Chem. B, 2006, 110, 13062.


59




Effect of multiple charge in adsorption of cationic surfactants

Grazyna Para1, Joanna Wegrzynska2, Kazimiera Anna Wilk2, Piotr Warszy ski1,*

1Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, Krakow, Poland, 2Faculty of Chemistry, Wroc aw University of Technology, Wroc aw, Poland.

The effect of divalent sulphate SO4

2- and carbonate anions CO32- on the surface tension of

cethyltrimethyl ammonium salts C16TABr (CTABr) and C16TAHSO4 (CTAHSO4), was investigated. The surface tension was determined by the pendant drop-shape analysis method. The “surface quasi two-dimensional electrolyte” (STDE) model of ionic surfactant adsorption, based on the assumption that the surfactant ions and counterions can undergo non-equivalent adsorption within the Stern at layer at air/solution interface, was extended for the description the adsorption of ionic surfactants in presence of multivalent electrolytes. The results indicate that a very good description of experimental data by the model can be achieved. They show that monovalent anions like Br-, Cl- or HSO4- ions decrease more effectively the surface tension of investigated surfactant than SO4

2- ions if the solutions of the same ionic strength are compared. That can be explained in terms of low ability of divalent SO4

2- ions to penetrate the surface layer due to their strong hydration. The STDE model of ionic surfactant adsorption was also applied for the description of the interfacial behavior of aqueous solution of bis- and tris-ammonium salts, specifically bis[2-hydroxy-3-(dodecyldimethyl-ammonio)propyl]alkylamine dichloride and bis[2-hydroxy-3-(dodecyldimethylammonio)propyl]dialkylammmonium trichloride. It was found that surface activities of divalent and trivalent surfactants were similar. Good agreement between theoretical results and experimental surface tension isotherms was obtained assuming that surfactant ion - counterion associates are formed in the solution. *Corresponding author: Email: [email protected], Phone: 0048 126395101, Fax: 0048 124251923.

60




Dynamics of thinning of foam films from -dodecyl maltoside ( -C12G2)

Silke Stöckle*, Rumen Krastev, Helmuth Möhwald

Max Planck Institute of Colloids and Interfaces, Potsdam, Germany.

Thin liquid films form the border between neighbouring non-coalescing colloidal species in colloidal systems. The surfactant concentration in the liquid phase determines the properties of these films. The thinning dynamics of foam films have become of more interest. We are utilising the thinning dynamics of thin liquid films as a tool to study the behaviour of liquid in confinement. The interplay of forces between the bulk and the liquid interfaces of the film hasbeen experimentally investigated for various systems and theoretical models have been found to describe the thinning [1]. The present contribution forms the background for future research on complex (particle loaded) or asymmetric (wetting) systems. We show first results on the dynamics of thinning of foam films stabilised by -C12G2. The -dodecyl-maltoside ( -C12G2) is a sugar based non-ionic surfactant. Its hydrophilic head group consists of two sugar rings connected via an ether bond. In our previous studies, we explored the properties of foam films stabilised by -C12G2. The gas permeability, the film thickness and the contact angle formed at the transition between the film and the bulk solution were measured as a function of the electrolyte concentration, surfactant concentration, and temperature [2-4]. The dynamic experiments were performed using the classical experimental technique developed by Scheludko [5]. Up-to-date theoretical analysis [1] was used to obtain the influence of the film surface dynamic properties on the film thinning.

The present results show the influence of the surfactant concentration on the thinning dynamics. The films formed from solutions with surfactant concentration above the critical micelle concentration show increased thinning speed the closer the film surfaces approach each other. The theoretical model describes the thinning procedure well only down to a certain thickness. Below that thickness the film tends to thin faster than the theory predicts. The discrepancy between theory and experiment could be explained by introducing additional term to the classical DLVO theory which counts for the short range interactions. Another possible explanation could be based on the difference in the viscous-elastic properties of liquids in confined volumes.

1. Danov K., Kralchevsky P., Ivanov I., In: Handbook of Detergents, Part A: Properties, G. Bronze, Ed., Marcel Dekker, New York, 1999, p. 303.

2. Muruganathan R. M., Krustev R., Ikeda N., Müller H. J., Langmuir, 2003, 19, 3062. 3. Muruganathan R. M., Krustev R., Müller H.-J., Möhwald H., Kolaric B., von Klitzing R.,

Langmuir, 2004, 20, 6352. 4. Muruganathan R. M., Krastev R., Müller H. J., Möhwald H., Langmuir, 2006. 5. Scheludko A., Adv. Colloid Interf. Sci., 1967, 1, 391-464.


61



Rhodia plenary lecture 4

Dynamical arrest in colloidal suspensions: From Wigner glasses to viscoelastic phase separation

Peter Schurtenberger*

Department of Physics and Fribourg Center for Nanomaterials, University of Fribourg, 1700 Fribourg, Switzerland.

Colloidal suspensions have frequently been used as ideal model systems to address fundamental issues in condensed matter physics such as liquid ordering, crystallization and glass formation. Particular attention has recently been given to fluid-solid transitions in colloids with short-ranged attraction, where for some appropriate choice of experimental conditions particles arrest and form disordered solids. Here I will concentrate on systems, where the presence of an additional weak long-ranged and soft repulsion leads to a particularly interesting state diagram, with the occurrence of a stable cluster phase and the possibility of a repulsive cluster glass at quite low concentrations.

1. Stradner A., Sedgwick H., Cardinaux F., Poon W. C. K., Egelhaaf S. U., Schurtenberger P., Nature, 2004, 432, 492.

2. Shalkevich A., Stradner A,, Bhat S. K., Muller F., Schurtenberger P., Langmuir, 2007, 23, 3570.

3. Cardinaux F., Gibaud T., Stradner A., Schurtenberger P., Phys. Rev. Lett., 2007, submitted.


62



Nanomaterials in pharmacy and biotechnology Keynote lecture 4.2

The influence of surface charge on the nanoparticle endocytosis mechanism

Oshrat Harush-Frenkel1,2, Yoram Altschuler2, Simon Benita1,*

1Department of Pharmaceutics, School of Pharmacy, The Hebrew University of Jerusalem, Jerusalem, Israel; 2Department of Pharmacology2, School of Pharmacy, The Hebrew University of Jerusalem, Jerusalem, Israel.

PEG-PLA nanoparticles (NPs) are attractive drug carriers owing to their minor toxic effect and their ability to associate and internalize into mammalian cells. A therapeutic obstacle in drug, protein and gene delivery is poor membrane permeation. Extensive research has shown that NPs endocytosis is a concentration, time and energy dependent process, suggesting an active saturable internalization mechanism [1]. The objective of the present study was to gain mechanistic insight on the molecular events of the endocytosis of either cationic or anionic PEG-PLA NPs into non polarized HeLa and polarized epithelial MDCK cells. For this purpose, cationic and anionic coumarin 6 loaded PEG-PLA NPs were prepared using the solvent-displacement method. The potential cytotoxic effects of NPs were evaluated using the well-known MTT approach. NPs were found to be non toxic to cells at the concentrations tested. The major endocytosis pathways in all cells are clathrin, caveole and dynamin dependent [2]. The endocytic pattern of labeled NPs was therefore investigated following adenoviruses mediated expression of dominant active and dominant negative mutants of the above mentioned and other endocytic polypeptides. Levels of endocytic polypeptide expression were assayed by Western blotting to validate the model. The exposed charge of NPs affected their capacity to internalize the cells, their intracellular localization as well as the cellular endocytic mechanism utilized [3]. In HeLa cells, anionic NPs exhibited inferior internalization profile of endocytosis compared to the cationic NPs whose uptake revealed a saturable non linear internalization pattern. Cationic NPs internalized both cell types via the clathrin mediated pathway. When this pathway was blocked in HeLa cells, NPs activated a compensatory endocytosis pathway that resulted in a higher cell accumulation of NPs [3]. Anionic NPs used the clathrin mediated endocytic machinery for their entry into polarized epithelial MDCK but not HeLa cells. In MDCK cells, a significant amount of NPs transcytosed and accumulated at the basolateral plasma membrane. Moreover, cationic NPs avoided the degradative lysosome pathway during their intracellular route in MDCK cells. These findings suggest that cationic NPs can be promising carriers for drugs that just barely penetrate the cells.

1. Panyam J., Labhasetwar V., Adv. Drug. Deliv. Rev., 2003, 55, 329. 2. Marsh M., Helenius A., Cell, 2006, 124, 729. 3. Harush-Frenkel O., Debotton N., Benita S., Altschuler Y., Biochem. Biophys. Res.

Commun., 2007, 353, 26.


63



Nanomaterials in pharmacy and biotechnology Contributed lecture 4.2.1

Insulin delivery from glucose-responsive microgels

Valérie Ravaine*, Véronique Lapeyre

Université de Bordeaux 1, CNRS, Institut des Sciences Moléculaires, Groupe Nanosystèmes Analytiques, site ENSCPB, 16 Av. Pey Berland, 33607 Pessac, France.

Monodispersed poly-N-isopropylacrylamide (p-NIPAM) submicronic microgels modified with a phenylboronic acid (PBA) derivative have been synthesized [1, 2]. These thermosensitive particles were found to be also glucose responsive at physiological pH and salinity, with a swelling degree proportional to the concentration of glucose. The particles were further assembled into thin films with a well-controlled thickness via the layer-by-layer (LBL) technique. The stimuli-responsive properties of the films were investigated by light scattering. Fluorescently-labeled insulin was loaded within the particles and insulin release was followed by fluorescence spectroscopy. Thermoresponsivity and sensitivity to the presence of glucose could be used to modify the film permeability and tune insulin release. The release kinetics was found to be triggered by both stimuli. The coupling between glucose concentration and insulin release kinetics represents a significant progress for diabetic patients as it opens the feasibility to design insulin self-delivering systems.

1. Lapeyre V., Gosse I., Chevreux S., Ravaine V., Biomacromolecules, 2006, 7, 3356.2. Lapeyre V., Ravaine V., Macromolecules, 2007, submitted.


64



Nanomaterials in pharmacy and biotechnology Contributed lecture 4.2.2

Evidence that drug molecules eat their way through membranes

Magdalena Baciu1,*, Sarra C. Sebai2, Xavier Mulet2, Oscar Ces2, James A. Clarke2, Robert V. Law2, Richard H. Templer2, Christophe Plisson3, Antony Gee3, Christine A. Parker3

1Institute for Physical Chemistry, University of Cologne, Cologne D-50939, Germany; 2Department of Chemistry, Imperial College London, London SW7 2AZ, UK; 3PET Imaging Department, GlaxoSmithKline, Addenbrookes Hospital, Cambridge CB2 2GG, UK.

Drug molecules must cross multiple cell membrane barriers in order to get to their site of action. We present evidence that one of the largest classes of pharmaceutical drug molecules, the cationic amphiphilic drugs1, or CADs, do so via a catalytic reaction that degrades the phospholipid fabric of the membrane. It is found that CADs partition rapidly (<150 ms) to the polar/apolar region of the membrane2. At physiological pH, the protonated groups on the CAD catalyse the acid-hydrolysis of the ester linkage present in the phospholipid chains, producing a fatty acid and single-chain lipid (see Fig. 1). The single-chain lipids rapidly destabilise the membrane, causing membranous fragments to separate and diffuse away from the host3. These membrane fragments carry the drug molecules with them. The entire process, from drug adsorption to drug release within micelles occurs on a timescale of seconds, compatible with in vivo drug diffusion rates4. Given the rate at which this occurs it is probable that this process is a significant mechanism for drug transport.

Fig. 1. The postulated mechanism of acid-catalysed hydrolysis of a phospholipid by haloperidol.

1. Reasor M. J., Kacew S., Exp. Biol. Med. 2001, 226, 825. 2. Kuroda Y., Kitamnura K., J. Am. Chem. Soc. 1984, 106, 1. 3. Bergstrand N., Edwards K., Langmuir 2001, 17, 3245. 4. Hukkanen J., Jacob P. III, Benowitz N. L., Pharmacol. Rev. 2005, 57, 79.


65



Nanomaterials in pharmacy and biotechnologyContributed lecture 4.2.3

Influence of surfactants on the encapsulation of perfluorooctyl bromide within polymeric capsules used as ultrasonic contrast agents.

Nicolas Tsapis*, Emilia Pisani, Juliane Paris, Catherine Ringard, Véronique Rosilio, Elias Fattal

Univ Paris-Sud, CNRS UMR8612, Faculté de Pharmacie, Châtenay-Malabry, France.

Ultrasonic imaging is a widely available, non invasive and cost-effective diagnostic modality, but vessels smaller than 200 microns in diameter are impossible to visualize. Commercial Ultrasound Contrast Agents (UCAs), consisting of encapsulated gas microbubbles injected intravenously, enable only a qualitative visualization of the microvascularization for a short period of time since they are rather unstable. In a strategy to develop more stable UCAs, we have designed a process to obtain nano/microcapsules with a single core of liquid perfluorocarbons within a biodegradable polymeric shell of homogeneous thickness. The polymer shell should improve the stability of the capsules as compared to UCAs stabilized by a monomolecular layer, while the acoustic impedance of the perfluorocarbons should insure their echogenicity. During the optimization of perfluorooctyl bromide (PFOB) encapsulation by solvent emulsion-evaporation, a marked influence of surfactants used during the emulsification step of the process has been observed. While sodium cholate leads to spherical capsules of homogeneous thickness, sodium taurocholate induces partial encapsulation of the PFOB droplet and polyvinyl alcohol to a coexistence of both morphologies. The influence of evaporation speed or surfactant concentration on final morphologies has been studied in detail. The theoretical model proposed by Torza and Mason [1] fails to explain theses morphologies. However, surface and interfacial tension measurements coupled to microscopic observations of the evaporation phase allow proposing an explanation of the observed morphologies.

Fig. 1. Examples of the different morphologies observed after solvent evaporation.

1. Torza S., Mason S. G., J. Colloid Interf. Sci., 1970, 33, 67.


66



Nanomaterials in pharmacy and biotechnologyContributed lecture 4.2.4

DNA gel particles: Particle preparation and release characteristics

M.Carmen Morán1,*, Jorge Costa-Pereira1, M. Graça Miguel1, Björn Lindman1,2

1Chemistry Department, Coimbra University, 3004-535 Coimbra, Portugal; 2PhysicalChemistry 1, Lund University, P.O. Box 124, 22100 Lund, Sweden.

Aqueous mixtures of oppositely charged polyelectrolytes undergo associative phase separation, resulting in coacervation, gelation or precipitation. This phenomenon has been exploited here to form DNA gel particles by interfacial diffusion. We report the formation of DNA gel particles by mixing solutions of DNA (either single- (ssDNA) or double-stranded (dsDNA)) with solutions of cationic surfactant CTAB and solutions of the protein lysozyme.

Under optimal conditions, droplets from DNA solutions instantaneously gellet into discrete particles upon contact with the corresponding surfactant or protein solution. The size of the resulting particle reflects the size of the parent drop and varies between 1 and 3 mm (Fig. 1 a). Fluorescente microscopy studies confirm the presence of DNA in the particles (Fig.1 b). Swelling, dissolution behaviour, surface morphology and release of DNA as well as the cationic compound indicate different interaction of ssDNA and dsDNA with both the surfactant and the protein. By using CTAB and lysozyme as the base material, the formation of a DNA reservoir hydrogel, without adding any kind of cross-linker or organic solvent was demonstrated.

a) b)

Fig. 1. Formation of DNA gel particles: a) CTAB-dsDNA particles. b) fluorescence micrograph of the CTAB-dsDNA particles in presence of the fluorescence dye, 4’-6-diamidino-2-phenyl-indole (DAPI).


67



Charging, adsorption, and energetics of interfaces Keynote lecture 4.3

Water surface is acidic

Victoria Buch,1 Anne Milet,2 Robert Vácha,3 J. Paul Devlin4, Pavel Jungwirth,3,*

1Fritz Haber Institute for Molecular Dynamics, Hebrew University, Jerusalem, 91904 Israel; 2LEDSS, Université Joseph Fourier, BP53, 38041 Grenoble , France; 3Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Molecular Systems, 16610 Prague 6, Czech Republic; 4Department of Chemistry, Oklahoma State University, Stillwater, Oklahoma 74078, USA.

Autoionization (autolysis) of water which gives rise to its pH is one of the key properties of aqueous systems. Surfaces of water and aqueous electrolytes solutions are traditionally viewed as devoid of inorganic ions, however, recent molecular simulations and spectroscopic experiments show the presence of certain ions including hydronium in the top-most layer. This raises the question about what is the pH of the surface of neat water. Microscopic simulations and measurements with atomistic resolution show that water surface is acidic due to a strong propensity of hydronium (but not of hydroxide) for the surface [1]. In contrast, macroscopic experiments, such as zeta potential and titration measurements, indicate a negatively charged water surface interpreted in terms of preferential adsorption of OH-. Here we present recent simulations and experiments characterizing autoionization at the surface of liquid water and ice crystals in an attempt to discuss in detail, if not fully resolve, the existing controversy.

Fig. 1. A typical snapshot from a molecular dynamics simulation showing a surface bound hydronium and bulk hydroxide.

1. Buch V., Milet, A., Vacha R., Jungwirth P., Devlin J. P., Proc. Natl. Acad. Sci. USA, in press.


68



Charging, adsorption, and energetics of interfaces Contributed lecture 4.3.1

On the charging process of minerals

Christophe Labbez*

Institut Carnot de Bourgogne, UMR 5209 CNRS, Université de Bourgogne, Dijon, France.

The failure of the DLVO theory to predict the stability of colloidal systems for highly coupled systems is well established. However, the limitations of the classical Stern model (CS) have not received the same attention. Recently, we have shown by experiments (titrations and electrophoresis) and Monte Carlo (MC) simulations on calcium silicate hydrate nanoparticles [1] that ionic correlations induced by multivalent cations can lead to extremely high surface charge densities and eventually to an apparent surface charge reversal of such particles. Unless an effective specific adsorption constant is used, the CS model is unable to predict these properties. In this work, we report results from MC simulations of the charging process as well as a comparison with the titration experiments [2,3] on silica particles in mono- and di-valent electrolytes. A new grand canonical titration method [4] was used in the simulations, where a microscopic model for the titration of the individual surface sites is developed. While it is generally believed that divalent counterions promote negative surface accumulation by cation-specific interactions, our MC simulations show that one single pK value and pure electrostatic interactions are enough to explain the observed titration experiments. Indeed, an excellent agreement is obtained between simulations and experiments for silica particles immersed in both sodium and calcium salt solutions. Another failure of the CS model concerns the charge regulation of charged particles upon separation in multivalent electrolytes. We will show that, in this context, the main accepted idea, which is a decrease of the surface charge density when decreasing the separation of two colloids bearing a charge of the same sign, is wrong. MC CS

1. Labbez C., Jönsson B., Pochard I., Nonat A., Cabane B., J. Phys. Chem., 2006, 110, 9219. 2. Dove P. M., Craven C. M., Geoch. Cosmo. Acta, 2005, 69, 4963. 3. Kobayashi M., Skarba M., Galletto P., Borkovec M., J. Colloid Interface Sci., 2005, 292,

139.4. Labbez C., Jönsson B., Lecture Notes Comp. Sci., 2007, in press.


69




Adsorption from binary fluids: The transition from critical to van der Waals wetting

J. Bowers1, A. Zarbakhsh2, I. A. McLure3, R. Cubitt4, J. R. P. Webster5,R. Steitz6, H. K. Christenson7,*

1Department of Chemistry, University of Exeter, Exeter EX4 4QD, UK, 2School of Biological and Chemical Sciences, Queen Mary University of London, London E1 4NS, UK, 3Department of Chemistry, The University of Sheffield, Sheffield S3 7HF, UK, 4Institut Laue-Langevin, BP-156, 38042 Grenoble, Cedex 9, France, 5ISIS Facility, CLRC Rutherford Appleton Laboratory, Chilton, Oxon OX11 0QX, UK, 6Berlin Neutron Scattering Center, Hahn-Meitner-Institut, D-14109 Berlin, Germany, 7School of Physics and Astronomy, The University of Leeds, Leeds LS2 9JT, UK

Most experimental and theoretical studies of adsorption from binary fluids have focussed on the critical regime and little work has been done on adsorption in other regions of the phase diagram. In an attempt to correct this imbalance we have used neutron reflectometry to study the composition profile at a solid surface (silicon coated with n-octadecyl chains) in the n-hexane/perfluoro-n-hexane system (critical temperature Tc = 22.6 °C, critical mole fraction of n-hexane H = 0.50). Measurements have been made at temperatures approaching coexistence from above, along three different isochores ( H = 0.50, 0.39 and 0.25) in the one-phase region. This is the “wet” side of the phase diagram, where there is a surface excess of n-hexane. The temperature dependence of the composition profile and the surface excess vary in a complex manner as the system moves away from criticality. The results show that surface effects on the composition profile in a binary fluid become very long range (> 100 nm) as phase coexistence is approached, even at compositions far from the critical. Although data in the non-critical regime are consistent with a z-3 decay of the composition profile, as expected for van der Waals forces, we cannot unambiguously assign a decay to the long-range 80 – 120 nm) region of the film. However, as expected for long-range van der Waals forces, the n-hexane surface excess increases as (T-T0)-1/3 near coexistence. At higher temperatures, where a transition to criticality is indicated, the decay of is steeper.


70




Electric breakdown of thin films: A microfluidic approach for stability measurement of water in oil emulsion films

Subir Bhattacharjee1,*, Farshid Mostowfi1, Jan Czarnecki2, Jacob Masliyah2

1Department of Mechanical Engineering, University of Alberta, 2Department of Chemical and Materials Engineering, University of Alberta, Edmonton, AB, Canada.

An experimental technique is developed for assessing stability of thin liquid films by application of electrical forces and simultaneous measurement of the electric conductivity of the system. The concept involves creating a thin film at the intersection of two micro-channels etched onto a glass substrate. Once a thin film is created, a ramped DC potential difference can be applied across it. The electrical stresses developed at the film interfaces lead to its rupture above a threshold potential. The potential at which the film ruptures is used to assess the stability of the film. Small channel dimensions in this microfluidic platform allow characterization of thin films formed between micron-sized droplets and high capillary pressures, which are difficult to attain using conventional thin film characterization techniques. The results of DC potential breakdown of films stabilized by lecithin, Tegopren®, and other commercial de-emulsifiers, show that critical potential can be considered as an extremely accurate measure of thin film stability. Stability measurements using this technique were in accord with Langmuir adsorption model for lecithin stabilized films. Furthermore, impedance spectroscopy was used on these microscopic films to measure capacitance of the films. The capacitance measurements led to the estimation of the film area. The effect of drainage time and adsorption time of films was also studied using impedance spectroscopy. Similar to DC measurements, capacitance measurements of the film also suggested a Langmuir adsorption trend for lecithin stabilized films. Moreover, capacitance measurement of films under the effect of DC potential was conducted. The results showed a dependence of capacitance to square of applied DC potential. The developed microfluidic system can serve as a rapid characterization technique that can be integrated into online detection and diagnostic techniques for a variety of commercial processes related to formation of emulsions and de-emulsification.


71




On the derivation of Young’s equation for sessile drops: Non-equilibrium effects due to evaporation

Hans-Jürgen Butt*, Dmytro Golovko, Elmar Bonaccurso

Max-Planck-Institute for Polymer Research, Mainz, Germany.

Sessile liquid drops have a higher vapor pressure than planar liquid surfaces, as quantified by Kelvin’s equation. In classical derivations of Young’s equation this fact is often not taken into account. For an open system a sessile liquid drop is never in thermodynamic equilibrium and will eventually evaporate. Practically, for macroscopic drops the time of evaporation is so long that non-equilibrium effects are negligible. For microscopic drops evaporation cannot be neglected. By confining a liquid to a closed system real equilibrium can be established. Experiments on the evaporation of water drops confirm the calculations.


72



Joint ECIS / COST plenary lecture 5

Adsorption of colloid particles at heterogeneous surfaces bearing sites of various shapes

Zbigniew Adamczyk*

Institute of Catalysis and Surface Chemistry Polish Academy of Sciences, ul.Niezapominajek 8, 30-239 Cracow, Poland.

Methods of theoretical and experimental evaluation of irreversible adsorption (deposition) of particles, e.g., colloids and globular proteins at surfaces bearing discrete adsorption sites of various shape were reviewed. The theoretical models were mainly based on the generalized random sequential adsorption (RSA) approach. Monte-Carlo type simulations performed according to this model enabled one to determine the initial flux, adsorption kinetics, jamming coverage and the structure of colloid particle monolayers formed at surfaces bearing adsorption sites in the form of spheres, disks, line segments (cylinders), semicircles and circles. Theoretical results obtained for various particle to the site size ratio, denoted by .and the site coverage s have been discussed. The effect of the site shape was extensively discussed. It was also predicted theoretically that in the case of <<1 (particle dimension much smaller than the site size) colloid particle deposition can be potentially used for imaging surface features of various shape. On the other hand, for comparable particle and site ratio, the adsorption kinetics and the jamming coverage increased significantly, at fixed site coverage with the parameter. Practically, for the jamming coverage of particles attained the value pertinent to continuous surfaces. These theoretical results suggested that spherically shaped sites were more efficient in binding particles in comparison with disk- shaped sites. It also was predicted that for particle size ratio < 4 the site multiplicity effect plays a dominant role, affecting significantly the structure of particle monolayers and the jamming coverage. Experimental results validating the main aspects of these theoretical predictions were also discussed. These results were mainly derived using monodisperse latex particles adsorbing on heterogeneous substrates produced by a controlled adsorption of sites of various shape. The spherically-shaped sites were produced by pre-adsorption of colloid particles of a desired size, coverage and surface charge. On the other hand, the disk- or linear segment sites could be produced by adsorption of polyelectyrolytes. Colloid particle deposition occurred under diffusion-controlled transport conditions and their coverage was evaluated by direct particle counting using the optical and electron microscopy. Adsorption kinetics was quantitatively interpreted in terms of numerical solutions of the governing diffusion equation with the non-linear boundary condition derived from Monte-Carlo simulations. It was proven that for site coverage as low as a few per cent the initial flux at heterogeneous surfaces attained the maximum value pertinent to homogeneous surfaces. It also was demonstrated that the structure of larger particle monolayers, characterized in terms of the pair correlation function, showed much more short-range ordering than predicted for homogeneous surface monolayers at the same coverage. Results pertinent to imaging of various nanosized surface features by colloid deposition were also discussed.

1s2

Acknowledgement: This work was supported by the MEiSzW Grant No.: N205 02231 1112.


73



Nanoparticles and their applicationsCOST workshop keynote lecture 5.2

Further progress in size and shape control for metal colloids

Luis M. Liz-Marzán*, Isabel Pastoriza-Santos, Jorge Pérez-Juste,Ana Sánchez-Iglesias, Enrique Carbó-Argibay

Departamento de Química Física y Unidad Asociada CSIC-Universidade de Vigo, 36310 Vigo, Spain.

We present in this talk a global view of the colloid-chemical synthesis of noble metal nanoparticles with controlled size and shape. Among the studied morphologies, spheres, rods, platelets and other polyhedrons are included, which can be prepared within a broad size range, within the nanometer scale. The interest of this synthetic control relies on the influence of nanoparticle morphology on the optical response, which is determined by the surface plasmon resonance of conduction electrons. In the figures we show examples of nanoparticles with several morphologies, as well as the characteristic extinction spectra for gold spheres, decahedra and rods with selected sizes, manifiesting the possibility to tune the position of the surface plasmon resonances basically at any wavelength within the visible and NIR spectral range.

300 400 500 600 700 800 900 10000.0

0.2

0.4

0.6

0.8

1.0 Au spheres Au decahedra Au rods

Abs

orba

nce

Wavelength (nm)

Fig. 1. a) TEM images of Au nanoparticles with various morphologies. b) UV-vis-NIR spectra of Au colloids with different particle size and shape.

1. Liz-Marzán L. M., Mater. Today, 2004, 7, 26. 2. Pérez-Juste J., Rodríguez-González B., Mulvaney P., Liz-Marzán L. M., Adv. Funct.

Mater. 2005, 15, 1065. 3. Liz-Marzán L. M., Langmuir, 2006, 22, 32. 4. Bastys V., Pastoriza-Santos I., Rodríguez-González B., Vaisnoras R., Liz-Marzán L. M.,

Adv. Funct. Mater. 2006, 16, 766. 5. Sánchez-Iglesias A., Pastoriza-Santos I., Pérez-Juste J., Rodríguez-González B., García de

Abajo F. J., Liz-Marzán L. M., Adv. Mater. 2006, 18, 2529.


74



Nanoparticles and their applicationsCOST workshop lecture 5.2.1

Oxide nanoparticles suspended in ionic solids: A potential self-repairing nanomaterial ?

Thomas Zemb1,*, J. N, Cachia1,2, Michel Wong Chi Man2, X. Deschanels1, John Bartlett3

1Institut de Chimie Séparative de Marcoule, Bagnols sur Cèze, France; 2Ecole Nationale supérieure de Chimie de Montpellier, Bagnols sur Cèze, France; 3Department of Chemistry, University of Western Sydne, Australia.

Self-repairing nanomaterials, based on hierarchical structures including colloid and a larger scale organization, inspired from nacre for instance, are emerging from fundamental knowledge of self-organization and forces between colloids, dispersed in complex fluids.

A recent example within the frame of the COST D43 participants is made of capsules made with alternated polyelectrolyte layers (Moehwald, Shchukin and co-workers). Alternated surfactants, as catanionic crystalline rotator phases are also patented in the field of corrosion and friction.

In ultra-long term protection against leaching of potentially dangerous ions, such as in nuclear waste management, two most explored technologies, i.e. glass including boron and zirconium as well as advanced vitro-ceramics known under the generic name of SYNROC also “self-repair”, since surface re-precipitation phenomenon as well as inhibition at nanometric scale of the propagation of cracks are involved.

The present theoretical work presents estimations of some constraints and possible perfomances of a class of materials which is made of colloidal oxides suspended in room temperature ionic liquids, or low temperature melting salts. It is expected that inside the COST D43 network, some similar materials will be synthetised. The first step is compatibilization between the colloid and the complex fluid used as “embedding host material” , and their evolution of microstructure linked to mechanical properties


75



Nanoparticles and their applications COST workshop lecture 5.2.2

Colloid chemistry applied to ceramic suspensions

Carmen Galassi*, Davide Gardini

Research Institute of Science and Technology for Ceramics, National Research Council (ISTEC-CNR) via Granarolo 64, I-48018 Faenza, Italy

Colloid chemistry is a powerful tool for the study and optimization of the ceramic processing as much as the powder particle size is decreased towards nanometric dimensions. Studies of the stability of oxide and nitride based suspensions were carried out towards solid content, particle size and morphology, type and quantity of deflocculant, mainly by zeta potential determination and rheological characterization. The interparticle interactions are often modified by the addition of polyelectrolytes that the change of the electrostatic potential and introduces steric hindrance. Calculation of potential energy of interaction by the DLVO theory showed the effectiveness of the addition of polyelectrolyte on the colloidal stability of hydroxiapatite powders with different surface reactivity (pHiep and - potential vs pH curves) related to the interplay of dissolution and adsorption of Ca2+ ions. Electrokinetic analysis of powder slurries with different deflocculants showed that anionic polyelectrolytes are the more effective dispersing agents [1]. The surface reactivity is strongly influenced by the synthesis method, and by the route of addition of small quantities of dopants or sintering aids; this effect was investigated by adding lanthanum and yttrium nitrates to Si3N4 by co-precipitation or different milling methods. Depending on the actual features of the starting Si3N4 powders the co-precipitation produced different relevant effects on the composition of the coating layer and the electrokinetic behavior of aqueous suspensions with coated powders depends greatly on the additives, their solubility and the rate of oxidation of the coated layer. The colloidal processing is applied to the optimization of several ceramic processes: the performance of nano-inks of different pigment compositions prepared with various solid loadings and their chemico-physical properties (particle size, viscosity, surface tension, -potential) were tailored for the ink-jet application. The nanometric pigments show a Newtonian behaviour and fulfil the viscosity and surface tension requirements of ink-jet applications in a range of printing temperatures [3].

1. Pretto M., Costa A. L., Landi E., Tampieri A., Galassi C., J. Am. Ceram. Soc., 2003, 86, 1534.

2. Bretoni F., Galassi C., Ardizzone S., Bianchi L. C., J. Am. Ceram. Soc., 1999, 82, 2653. 3. Dondi M., Matteucci F., Gardini D., Blosi M., Costa A. L., Galassi C., Baldi G., Barzanti

A., Cinotti E., Adv. Science Technology, 2006, 51, 174.


76




Solid phase organocatalysis

Finn K. Hansen1,*, Tore Hansen1, Tor Erik Kristensen1, Steinar Pedersen2

1Department of Chemistry, University of Oslo, Norway; 2Hydro Polymers, Porsgrunn, Norway.

Organocatalysis is a quite novel research field within asymmetric organic synthesis. Instead of the traditional metal based catalysts, small organic molecules, e.g. amino acids, have been shown to give interesting results. This has several advantages such as low cost, potential use in aqueous solutions, better biodegradability, no traces of metals and less health risk due to mild conditions. Almost all known organocatalytic processes are presently carried out under homogenous conditions. In order to increase the usability of these processes in practical applications, a heterogeneous catalytical process is necessary, but this has not yet been utilised significantly in organocatalysis. Different solid supports are used in bio-organic processes such as peptide synthesis, chromatography, ion exchange etc. These are either based on macroporous silica or solid or macroporous cross linked polymer particles. We have for many years been producing large (5 – 50 m) monodisperse macroporous polymer particles based on the Ugelstad method and similar processes for chromatography, biomedicin etc. These particles can be given functional groups such as double bonds, chloromethyl, hydroxyl, carboxyl, glycidyl, etc. which can be used to immobilize the organocatalysts. Different types of grafting can also be performed. The activity of these solid phase catalysts will be dependent of the type of catalyst, the structure of the particles, the method of binding, the degree of functionalization, etc. In this talk we will give a review of these methods and some recent results from the project.


77




Microgel particles for controlled uptake and release

Brian Vincent*

School of Chemistry, University of Bristol, Bristol, BS8 1TS, UK.

Microgel particles are particles of cross-linked polymers, copolymers or polyelectrolytes,dispersed in a solvent medium, which swell (with solvent) and deswell in response to changes in the local thermodynamic conditions [1]. Triggers for such a response include temperature, solvent composition and light, and in addition, for polyelectrolyte-based systems, pH and ionic strength. In this lecture several types of microgel system will be discussed, including those based on poly(N-alkylacrylamides), poly(vinyl pyridine), and amphoteric systems. Fig. 1 shows swollen poly(N-isopropylacrylamide microgel particles deposited on an SEM grid and dried prior to imaging. Both the equilibrium swelling and swelling/deswelling kinetics of microgel particles will be discussed. Microgel particles provide interesting systems for controlled uptake / release. An overview will be presented in regard to the uptake and release of polymers, surfactants and nanoparticles, with potential applications in a wide range of technologies, from drug delivery to the controlled release of bactericides, perfumes and flavours.

Fig. 1. SEM image of (dried) polyNIPAM microgel particles deposited on a grid.

1. Saunders B., Vincent B., Adv. Colloid Interface Sci., 1999, 80, 1.


78



Self-assembly processes at interfaces Keynote lecture 5.3

The interaction of polyelectrolytes and surfactants at interfaces

Robert K.Thomas1,*, Jeffrey Penfold2, Diana Taylor1

1Physical & Theoretical Chemistry Laboratory (University of Oxford), South Parks Road, Oxford, UK; 2ISIS, STFC, Rutherford Appleton Laboratory, UK.

Polylectrolytes and oppositely charged surfactants interact very strongly and the interaction has been widely studied. However, the consequences of this interaction for the surface properties of polyelectrolyte/surfactant mixtures have been less well explored. Neutron reflection work on a variety of systems shows that the behaviour at the air/water interface is determined approximately by a competition between the relative stability of surface complexes and bulk complexes, with one pattern of surface properties being produced when the former are more stable, and another when the latter are more stable. A survey of results from the two types of system will be presented and the extent to which they can be described quantitatively will also be discussed. These will include results from DNA/cationic surfactant mixtures, which also fit well into the general pattern, and results from mixtures of surfactants, which allow a tuning of the strength of the interaction between polyelectrolyte and surfactant.


79



Self-assembly processes at interfaces Contributed lecture 5.3.1

Dynamic surface elasticity of nanoheterogeneous polyelectrolyte/surfactantadsorption layers at the liquid – gas interface

Boris Noskov1,*, Alexander Akentiev1, Shi-Yow Lin2, Giuseppe Loglio3, Reinhard Miller4

1Department of Colloid Chemistry, St. Petersburg State University, Russia, 2National Taiwan University of Science and Technology, Taipei, Taiwan, 3University of Florence, Florence, Italy, 4Max Planck Institut für Kolloid- und Grenzflächenforschung, Potsdam, Germany.

Although properties of polyelectrolyte/surfactant adsorption layers at liquid/fluid interfaces are crucial for numerous technological applications, the interfacial tension measurements have been practically the only experimental technique applied to these systems for many years. Recent experimental studies by more powerful methods demonstrated diverse structures of such layers [1]. At the same time most of the methods were not sensitive to the microscopic variation of surface properties along the interface. Only large fluctuations of the ellipsometric signal gave indirect evidence of the surface microheterogeneity and microparticle formation [2,3]. One can also explain the complex dependency of the dynamic surface elasticity of sodium polystyrenesulfonate/dodecyltrimethylammonium bromide (DTAB) adsorption layers on surfactant concentration by a transition between nanoheterogeneous and micro-heterogeneous surface layers [4]. In order to elucidate the formation of nano- and microstructures in the polyelectrolyte/surfactant adsorption layers further the solutions of the complexes between polydiallyldimethylammonium chloride and sodium dodecylsulfate sulfate (SDS), polyvinylpyridinium chloride and SDS, statistical copolymers of sodium polyacrylamidopropansulfonate with N-isopropylacrylamide and SDS were studied by the capillary waves, oscillating barrier, drop and bubble methods. All the systems exhibited an abrupt transition between regions of high and low surface elasticities thus indicating the formation of microgels. The presence of nanoparticles at the liquid surface was confirmed by transferring the films onto a solid support and investigating them by transmission electron microscopy.

Acknowledgement: This work was financially supported by the National Taiwan University of Science and Technology (Project NTUST-2007-R-06), the National Science Council of Taiwan, the Russian Foundation of Basic Research (Joint Project No. 05-03-90580 HHC_a) and the European Space Agency (AO-99-052).

1. Taylor D. J. F., Thomas R. K., Penfold J., Adv. Colloid Interface Sci., 2007, in press. 2. Monteux C., Williams C., Meunier J., Anthony O., Bergeron V., Langmuir, 2004, 20, 57. 3. Noskov B. A., Grigoriev D. O., Lin S.-Y., Loglio G., Miller R., Langmuir, 2007,

submitted. 4. Noskov B. A., Loglio G., Miller R., J. Phys. Chem. B, 2004, 108, 18615.


80




The adsorption, deformation and rupture of lipid vesicles at solid surfaces

Richard Kik, Mieke Kleijn*, Frans Leermakers

Laboratory of Physical Chemistry and Colloid Science, Wageningen University, Wageningen, The Netherlands.

The adhesion of lipid vesicles to surfaces is a rather interesting process, generically as well as in view of possible applications. However, until now a lot of the principles behind it are poorly understood. Why, for instance, is it that on some surfaces vesicles do adsorb intact, while on other surfaces adsorbed vesicles transform into a supported bilayer? We address this question experimentally, by studying the adsorption of dioleoyl phosphatidylglycerol (DOPG) and dioleoyl phosphatidylcholine (DOPC) vesicles to gold, as well as theoretically, by using a self-consistent field (SCF) model that takes into account molecular details of the bilayer. Adsorption studies were performed using a quartz crystal microbalance (QCM), which gives the adsorbed mechanical mass, and by surface plasmon resonance (SPR) measurements of the adsorbed lipid mass. By combining these techniques it is possible to quantify the amount as well as the degree of deformation of the adsorbed vesicles. Results show that the deformation increases with vesicle size. Adsorption of DOPC vesicles with a radius larger than about 40 nm results into a fully covered surface, while below this radius it is only partly covered. These size-effects are confirmed by SCF calculations, which further show that there are three regimes for adsorption: i) the interaction with the surface is too weak to deform the vesicles and no adsorption takes place; ii) moderate interaction leading to adsorption of intact vesicles; interaction energy and penalty for deformation are balanced in such a way that the total adsorption energy is independent of bilayer elasticity; iii) strong interaction; an adsorbed bilayer patch is more favourable than an adsorbed vesicle. See Figures 1 and 2.

Fig. 1 Fig. 2Fig. 1 Fig. 2

Fig. 1. Deformation of an adsorbed vesicle (1000 lipids with C18 tails) as calculated using SCF theory. Dimensions of r and z axes in lattice layers. a) Weak lipid-surface interaction; b) strong interaction; bending at the edges involves drastic structural changes in the bilayer leading to instability and rupture.

Fig. 2. Total adsorption energy F as a function of lipid-surface interaction G (both in kTper unit area). For stronger interactions ( G more negative) formation of a bilayer patch becomes more favourable.


81




Pickering emulsions: The role of surface coverage on their original properties

Véronique Schmitt1,*, Florent Gautier1, Joanna Giermanska1, Stéphane Arditty1,Serge Ravaine1, Fernando Leal-Calderon2

1Centre de Recherche Paul Pascal, Université Bordeaux I - CNRS, avenue Dr A. Schweitzer, 33600 Pessac, France; 2Laboratoire des Milieux Dispersés Alimentaires, ISTAB, Université Bordeaux I, avenue des Facultés, 33400 Talence, France.

Pickering emulsions are surfactant-free emulsions, stabilized solely by colloidal particles. It is possible to produce monodisperse Pickering emulsions by exploiting the phenomenon of limited coalescence. If the total amount of particles is initially insufficient to protect the interfaces, the emulsion droplets coalesce such that the total interfacial area between oil and water is progressively reduced. Since the adsorption of particles at the interface is irreversible, the degree of surface coverage by them increases until coalescence is halted. Following this process, a large variety of materials can be obtained (direct, reverse, multiple) in a wide range of diameters (1 µm to 1 cm). Once stabilized, such emulsions exhibit exceptionally high stability and bulk elasticity.

In order to investigate the role of surface coverage (defined as the ratio of interface area covered by the particles to the total interface area) on the original properties, we synthesized particles whose interactions at the interface can be tuned by an external field (pH, ionic strength). We show that, when the particles are densely packed at the oil-water interface, the bulk elasticity and osmotic resistance are not controlled by interfacial tension as for classical surfactant-stabilized emulsions, but by the interfacial elasticity resulting from the strong attractive interactions between the solid particles adsorbed at the oil-water interface. The oil-water interface exhibits a 2D plastic behavior at the origin of the unusual properties. Pickering emulsions characterized by a surprising low surface coverage can also be stabilized with the same particles, leading to emulsions with different properties (drops size, interfacial behavior…) see Fig. 1. We discuss the origin of this astonishing stabilization.

a) b) Fig. 1. Influence of the pH on the emulsion drop size (a) pH=4, (b) pH=6


82




Foams derived from particle suspensions

Ludwig Gauckler*

Department of Materials, ETH Zürich, Zürich, Switzerland.

Liquid foams and emulsions are technically and commercially important soft matter. The thermodynamically unstable nature of liquid foams is a critical issue in all applications. Surfactants, biomolecules and colloidal particles have long been known to stabilize oil droplets in Pickering emulsions [1]. Partially hydrophobic particles can also attach to gas–liquid interfaces and stabilize air bubbles in surfactant-free diluted suspensions [2].The latter requires an optimum balance between the solid– liquid, solid–gas, and liquid–gas interfacial tensions and the capillary forces in the particle stabilized foam lamella.

We report about the criteria of particle stabilized liquid foams. The stability of such foams is strongly dependent on the wetting behavior of the particle surface. We control the particle surface energies by short - chain carboxylic acids, alkyl gallates and alkyl amines. They are appropriate amphiphiles to partially hydrophobize the surface of different inorganic particles in water and oil. For that purpose, the functional groups of the amphiphilic molecule were tailored according to the surface chemistry of the particles. A simple and versatile method then reported to prepare ultra stable particle-stabilized foams that percolate throughout the entire liquid phase and exhibit no drainage or creaming effects [3].

We describe the foaming behavior of air-particle suspensions as well as the preparation of air-oil-particle suspensions and the properties of the resulting foams including their stability. The universal nature of this method is demonstrated by foaming so different materials as oxide particles in aqueous media, polymers in apolar media, metal powders, cements and slag components. All these materials can easily be made to foams independent of their initial wetting behavior. New applications of this method in many different areas are explored now. Fig. 1. Different length scales in the particle stabilized foam.

1. Ramsden W., Proc. R. Soc. London, 1903, 72, 156; Pickering S. U., J. Chem. Soc., 1907, 91, 2001.

2. Exerowa D., Kruglyakov P. M., Colloids Surf. A, 2005, 263, 330-335; Weaire D., Hutzler S., The Physics of Foams, Oxford University Press, Oxford, UK, 2000.

3. Gonzenbach U. T., Studart A. R., Tervoort E., Gauckler L. J., Langmuir, 2007, 23, 1025; Gonzenbach U. T., Studart A. R., Tervoort E., Gauckler L. J., Langmuir 2006, 22, 10983; Gonzenbach U. T., Studart A. R., Tervoort E., Gauckler L. J., Angew. Chem. Int. Ed. 2006, 118, 1.


83



Interfaces and responsive systems COST workshop keynote lecture 6.2

Formation and coexistence of crystallites and micelles in carboxylate soap solutions and their effect on the solution’s pH and surface tension

Peter A. Kralchevsky1,*, Krassimir D. Danov1, Mariana P. Boneva1, Nikolay C. Christov1,Cenka I. Pishmanova1, Stefka Kralchevska1, Kavssery P. Ananthapadmanabhan2, Alex Lips2

1Laboratory of Chemical Physics & Engineering, Faculty of Chemistry, University of Sofia, Sofia, Bulgaria, 2Unilever Research & Development, Trumbull, Connecticut 06611, USA.

The sodium and potassium alkanoates (laurates, myristates, palmitates, stearates, etc.) have attracted both academic and industrial interest because of their application in many consumer products: soap bars; cleaning products; cosmetics; facial cleaners; shaving creams; deodorants, etc. The dissolution of such alkanoates (carboxylates) in water is accompanied by increase of pH, which is due to protonation (hydrolysis) of the alkanoate anion. Depending on the surfactant concentration, the investigated solutions contain precipitates of alkanoic acid, neutral soap and acid soaps. The latter are complexes of alkanoic acid and neutral soap with a definite stoichiometry. A method for identification of the different precipitates from the experimental pH isotherms is developed [1]. It is based on the analysis of precipitation diagrams, which represent plots of characteristic functions. For example, in the solutions of sodium myristate, we identified the existence of concentration regions with precipitates of myristic acid; 4:1, 3:2 and 1:1 acid soaps, and coexistence of two solid phases: 1:1 acid soap and neutral soap (Fig. 1). The solubility products of the precipitates have been determined and interpreted in terms of a theoretical model. The kinks in the surface-tension isotherms of the investigated solutions correspond to some of the boundaries between the regions with different precipitates and/or micelles in the bulk. Special attention is paid to the coexistence of two types of crystallites or of crystallites and micelles in these solutions, and to their solubilization ability.

(a) (b) (c)

Fig. 1. Crystallites in solutions of sodium myristate: (a) plate-like crystallites of 1:1 acid soap; (b) fiber-like crystallites of neutral soap, and (c) their coexistence.

1. Kralchevsky P. A., Danov K. D., Pishmanova C. I., Kralchevska S. D., Christov N. C., Ananthapadmanabhan K. P., Lips A., Langmuir 2007, 23, 3538.


84



Interfaces and responsive systems COST workshop lecture 6.2.1

Reflectometry: A versatile tool to characterize particulate coatings

Ger Koper*

DelftChemTech, Delft University of Technology, Delft, The Netherlands.

The optical properties of colloidal films with thicknesses ranging from less than one nanometer – formed by dendrimer molecules – to over one micrometer – formed by proteins and latex particles – are discussed. The experimental technique used is scanning angle reflectometry that is shown to provide extremely accurate information on dielectric thin films. Even though the analysis of these properties requires sophisticated electromagnetic theory, simple approximations have been derived and their use is demonstrated. As an example, the static and kinetic properties of dendrimer adsorption are presented.


85




Surface dynamics of mixed surfactant adsorption layers

Reinhard Miller1,*, Valentin B. Fainerman2, Volodja I. Kovalchuk3,Eugene V. Aksenenko4, Elena Mileva5, Jordan G. Petkov6, Libero Liggieri7

1Max-Planck-Institut für Kolloid- und Grenzflächenforschung, Potsdam, Germany; 2MedicalPhysicochemical Centre, Donetsk Medical University, Donetsk, Ukraine; 3Institute of Biocolloid Chemistry, Kiev, Ukraine, 4Institute of Colloid Chemistry and Chemistry of Water, Kiev, Ukraine; 5Institute of Physical Chemistry, Bulgarian Academy of Sciences, Sofia, Bulgaria; 6Unilever R&D Port Sunlight, Bebington, UK, 7 CNR, Istituto per l’Energetica e le Interfasi, Genoa, Italy.

Although there are many studies of surfactant adsorption layers at liquid interfaces, systematic investigations on the thermodynamics, kinetics and rheological properties of mixed adsorption layers are rare. Most practical applications are based, however, on the action of surfactant mixtures where each component plays a specific role in the typically very complex processes going on in modern technologies. Thus, a quantitative understanding of mixed surfactant adsorption layers is required.

The general picture for the equilibrium and non-equilibrium behaviour of liquid surface layers formed from mixed surfactant solutions has been developed recently, which includes equations of state [1], adsorption dynamics [2,3] and dynamic surface dilational rheology [4].

The corresponding theoretical results are presented and compared with experimental data obtained by the maximum bubble pressure and drop and bubble profile tensiometry. These methods provide data on the adsorption dynamics in a time window between milliseconds and hours (suitable to extrapolate equilibrium values at infinitely long adsorption times). The drop and bubble profile analysis combined with capillary pressure measurements allows for slow and fast harmonic surface perturbations leading to the dilational elasticity and viscosity of the interfacial layers (in a frequency range between 0.001 Hz up to 100 Hz). The experiments were performed with the non-ionic surfactants of the type Cn dimethyl phosphine oxides and CnEOm, and their mixtures at different mixing ratios. It will be demonstrated that the elaborated approach has the capacity of describing the equilibrium, dynamic and rheological behaviour of mixed systems by using essentially the knowledge of the interfacial characteristics of the individual components.

1. Fainerman V. B., Miller R., Aksenenko E.V., Adv. Colloid Interface Sci., 2002, 96, 339. 2. Frese C., Ruppert S., Sugár M., Schmidt-Lewerkühne H., Wittern K. P., Fainerman V. B.,

Eggers R., Miller R., J. Colloid Interface Sci., 2003, 267, 475. 3. Miller R., Fainerman V. B., Aksenenko E. V., Colloids Surfaces A, 2004, 242, 123. 4. Aksenenko E. V., Kovalchuk V. I., Fainerman V. B., Miller R., J. Phys. Chem., 2007,

submitted.


86




Nanostructured emulsions as potential delivery systems for functional molecules and

basis for transfer studies

Otto Glatter1,*, Christian Moitzi1,2, Samuel Guillot1,3, Matija Tomši 1, Stefan Salentinig1

1Department of Chemistry, University of Graz, Graz, Austria; 2Department of Physics, University of Fribourg, Fribourg, Switzerland; 3CRMD, University of Orléans, Orléans, France.

In this contribution we present our latest results on hierarchically organized fluid particles, i.e., sub-micron sized droplets kinetically stabilized as an aqueous emulsion having a self-assembled nanostructured interior [1-7]. These systems were investigated by small angle X-ray scattering (SAXS), cryogenic transmission electron microscopy (Cryo-TEM) [7], and dynamic light scattering (DLS). The nanostructures in the kinetically stabilized particles are thermodynamic equilibrium structures. Recently we reported on the effect of varying temperature [1], solubilizing tetradecane [2] and changing oil type or monoglyceride purity [3,4] on the reversible structural transitions of the nanoscale interior domains of kinetically stabilized monolinolein (MLO)-based particles. We found that it is possible even at room temperature to emulsify W/O microemulsion systems by the addition of tetradecane (TC) to the MLO-water system [2]. The addition of TC induces a transition of the internal particle nanostructure from continuous Pn3m (cubosomes) to H2 (hexosomes) and W/O microemulsions (EMEs) at a given temperature. The incorporation of the diglycerol monooleate in the system shows a counter effect to that of TC and allows us to tune back the self-assembled nanostructure in the TC-loaded dispersions from H2 to Im3m [4]. We will also present TC-loaded particles with confined structure of Fd3m (discontinuous micellar cubic phase) [5]. Namely, we found that the addition of TC induces a transition of the internal particle nanostructure from Pn3m to H2, and via Fd3m to EMEs at a given temperature.

Most interestingly, these systems allow us to study transfer of lipidic phases or of other molecules inserted to the interior of the droplets. After mixing two solutions with different loadings, one can measure the kinetics of transfer and equilibration if the internal structure depends on the solubilized materials [6]. So such hierarchically organized systems offer a unique possibility to study transfer between sub-micron sized confinements embedded in a continuous outer phase. In addition, these particles are potential candidates for carrier systems for functional molecules. These molecules can be lipophilic, amphiphilic or hydrophilic. 1. de Campo L., et al., Langmuir, 2004, 20, 5254. 2. Yaghmur A., et al., Langmuir, 2005, 21, 569. 3. Guillot, S., et al., Colloid. Surfaces A, 2006, 78, 291. 4. Yaghmur A., et al., Langmuir, 2006, 22, 9919. 5. Yaghmur A., et al., Langmuir, 2006, 22, 517. 6. Moitzi C., et al., Adv. Materials, 2007, in press. 7. Sagalowicz L., et al., J. Microscopy, 2006, 110, 221. *Corresponding author: Email: [email protected], Phone: 0043 3163805433, Fax: 0043 3163809850.

87




Novel polymer composites as promising smart materials

Miklós Zrínyi*

Department of Physical Chemistry and Materials Science, Laboratory of Soft Matters,Budapest University of Technology and Economics, Budapest, Hungary.

Colloidal (nano-) particles with special electric and magnetic properties were built into flexible polymer matrix. The particles couple the shape of the gel (or elastomer) to the external fields. Shape distortion occurs instantaneously and disappears abruptly when electric- or magnetic field is applied or removed, respectively. This abrupt shape transition can be applicable to a variety of fields as a new driving mechanism and can be exploited to construct new type of soft actuators, valves, colloidal motors as well as vehicles for controlled drug delivery.

Quincke rotation is the rotation of non-conducting objects immersed in liquid dielectrics and subjected to a strong homogeneous DC electric field. The rotation is spontaneous when the field exceeds a threshold value. Wide range of applications (e.g. microscopic motor) motivates researchers to find materials with micro-fabrication possibilities. Polymer composites that fulfil these requirements have been developed for the first time. Electro-rotation of disk shaped polymer composites is studied as a function of electric field intensity.

Magnetic and electric field induced deformation, locomotion and rotation, as well as on/off switching control of magnetic polymeric membranes will be the subject of the oral presentation.

1 2 3 40.0

0.5

1.0

1.5

[Hz]

E [106 V/m]

gelatine

PVA

Fig. 1. Top view of a rotating gelatine based composite in linseed oil (left) and dependence ofangular velocity on the DC electric field intensity (right).


88



Self-assembly of surfactants and polyelectrolytesKeynote lecture 6.3

Polyelectrolyte/surfactant aggregates: Influence of the polymer backbone rigidity

Siwar Trabelsi, Daragh McLoughlin, Samuel Guillot, Dominique Langevin*

Laboratoire de Physique des Solides, Université Paris Sud, Orsay, 91405 France.

Studies of aqueous solutions of polyelectrolytes and surfactants of opposite charges will be presented. Various techniques have been used : specific electrodes, scattering of light, X-ray and neutrons, electrophoretic mobility. We will show results obtained with cationic surfactants and anionic polyelectrolytes of different backbone rigidity, including DNA. In some cases, we find well defined aggregates, with a size controlled by the surfactant concentration. These aggregates possess an internal structure, similar to that of the liquid crystalline phases obtained in the precipitated phases obtained at higher surfactant concentrations.

*Corresponding author: Email: [email protected] Phone: 0033 169155351, Fax: 0033 169156086.

89



Self-assembly of surfactants and polyelectrolytes Contributed lecture 6.3.1

A new family of cubic phases stable at low temperatures

Masakatsu Hato1,* Jun Yamashita1, Manzo Shiono2

1Nanotechnology Research Institute, AIST. Tsukuba Central-5, Higashi 1-1-1, Tsukuba, Ibaraki, 305-8565, Japan; 2Present address: Riken Yokohama Institute, Genomic Sciences Center; 3New Business Development Division, Kuraray Co., Ltd. 1-1-3, Otemachi, Chiyoda-ku, Tokyo 100-8115, Japan.

Inverted cubic phases (QII) in lipid/water systems, in particular, those that are stable in equilibrium with excess water have unique features favouring their growing interest in biophysical and pharmaceutical fields. Owing to high values of Krafft temperatures, TK, of cubic phases forming lipids, however, the cubic phases currently available are generally unstable at low temperatures 0~4 C. This has hampered their biological applications, where low temperature operations are prerequisite for manipulating temperature sensitive actives.

With a view to developing a new family of cubic phases with low temperature stability, we have synthesized a series of lipids with hydrophobic chains in a range C12~C18, and their aqueous phase behaviour has been examined over a temperature range –40 C to 65 C by using optical microscopy, differential scanning calorimetry (DSC), and small angle X-ray scattering (SAXS) techniques. Given a hydrophobic chain type, the preferred phase consistently follows a phase sequence of an inverted hexagonal phase (HII) to a bicontinuouscubic phase (QII) to a lamellar phase (L ) as the size of the head group increases. On the basis of molecular structure-aqueous phase structure relationship obtained, we have discovered more than10 lipid species that form inverted cubic phase in excess water. Moreover, the values of TK of the cubic phase forming lipids are all below 0 C. The new cubic phases exhibit exceptional stability in the low temperature range, 0~4 C, and may be useful in pharmaceutical or biological applications.

-40 -30 -20 -10 0 10Temperature (oC)

(a)

0.1

(J/K

)

Fig. 1. DSC thermorgam of a C18-lipid (TK= 33 C).

*Corresponding author. Email: [email protected], Phone: 0081 0443557171.

90



Self-assembly of surfactants and polyelectrolytes Contributed lecture 6.3.2

Studying morphology and structure of micrometric helices of nucleo-amphiphiles

Carole Aimé1,*, Takao Sato1, Sabine Manet1, Damien Van Effenterre2, Reiko Oda1

1Chimie et Biologie des Membranes et Nano-objets UMR CNRS 5248, Institut Européen de Chimie et Biologie, 2 rue Robert Escarpit 33607 Pessac, 2Centre de Recherche Paul Pascal UPR CNRS 8641, 115 Av. Dr A. Schweizer 33600 Pessac, France.

We study the self-assembly behavior of cationic nucleo-amphiphiles in solution. By functionalizing the amphiphiles with biomolecules such as nucleotides, we attempt to mimic the structure formation and functions of biological systems in order to design and construct new molecular assemblies. These amphiphiles form micrometric helices in certain conditions. We aim at understanding how different parameters play roles in the formation of these architectures. We are able to tune the morphology of these aggregates playing with various parameters such as the nucleotide complexed, the concentration, the time, the temperature and the additives. Additionally, we study the deformability of these helices by micromanipulation [1]. These objects are highly extensible and return basically to their native shape after being stretched (see Fig 1). We now attempt to quantitatively study their elasticity.

10 µm 10 µm 10 µm

Fig. 1. Optical microscopy images of helices obtained by complexing nucleotides to cationic amphiphiles.

1. Houchmandzadeh B., Marko J. F., Chatenay D., Libchaber A., J. Cell Biol., 1997, 139, 1.


91



Self-assembly of surfactants and polyelectrolytesContributed lecture 6.3.3

Self-assembly in an asymmetric catanionic surfactant:Unusual lamellar-lamellar coexistence and vesicle-micelle transition

Bruno B. Silva1, Eduardo F. Marques1,*, Ulf Olsson2

1Centro de Investigação em Química, Department of Chemistry, Faculty of Sciences, University of Porto, Rua do Campo Alegre, nº 687, P-4169-007 Porto, Portugal; 2PhysicalChemistry 1, Centre for Chemistry and Chemical Engineering, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden.

Salt-free catanionic surfactants can be prepared from the equimolar mixing of oppositely charged amphiphiles followed by inorganic counterion removal[1]. Compared with catanionic mixtures, true catanionic surfactants in water constitute binary systems and, as a consequence, they have the advantage of being simpler to investigate. The coexistence of two equilibrium lamellar liquid crystalline phases in binary surfactant-water systems is a rare and still puzzling phenomenon [2]. In the few binary systems where it has been experimentally demonstrated, the surfactant is invariably ionic and the bilayer coexistence is supposed to originate from a delicate balance between attractive (van der Waals) and repulsive (electrostatic and short-range repulsive) forces.

In this work, we report for the first time a lamellar-lamellar coexistence for a catanionic surfactant (the asymmetric compound hexadecyltrimethylammonium octylsulfonate [3]) in water. Small angle-X ray scattering, polarizing light microscopy and 2HNMR unequivocally show the coexistence of a dilute (or swollen) lamellar phase, L ’, and a concentrated lamellar (or collapsed) lamellar phase, L ’’. Linear swelling is observed for the two phases, with the miscibility gap in between (15-54 wt % surfactant). Theoretical calculations on the balance of forces will be presented, in an attempt to account for the phase coexistence.

In the more dilute region the swollen lamellar phase is in equilibrium with an isotropic solution region, containing elongated micelles. Vesicles can be observed in this two-phase region, as a stable dispersion of L ’ in the solution phase. Furthermore, upon temperature increase a vesicle-to-micelle transition occurs. The structural properties of the formed aggregates and the nature of the phase transition have been investigated by means of microscopy, calorimetry, light scattering and self-diffusion NMR.

1. Marques E. F., Regev O., Khan A., Lindman B., Adv. Colloid Interface Sci, 2003, 100, 83.

2. Noro, M. G., Gelbart, W. M., J. Chem. Phys., 1999, 111, 3733. 3. Silva B. B., Marques E. F., J. Colloid Interface Sci. 2005, 290, 257.


92



Self-assembly of surfactants and polyelectrolytesContributed lecture 6.3.4

New routes to polymer self-assembly into nano-sized water soluble particles

Marián Sedlák1,*, estmír Ko ák2

1Institute of Experimental Physics, Slovak Academy of Sciences, Košice, Slovakia; 2Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Prague, Czech Republic.

New routes to polymer self-assembly will be introduced: (i) self-assembly of polycarboxylic acids and (ii) self-assembly of block copolymers of polycarboxylic acids. In both cases the complexation is based on the balance of hydrogen bonding and hydrophobic interactions. The route to the self-assembly of poly(carboxylic acids) is based on the following idea. This class of polymers (e.g. poly(methacrylic acid), poly(ethacrylic acid) or poly(propylacrylic acid)) exhibits so called lower critical solution temperature (LCST), which means that solutions undergo a macroscopic phase separation above LCST. The solvent quality worsen upon heating and polymer-polymer contacts are preferred over polymer-solvent contacts, which leads to the formation of polymer assemblies slightly below LCST. Upon subsequent cooling to normal laboratory temperature, the assemblies should eventually dissolve, however, this is not the case. The reason is that polymer chains brought to a close proximity at elevated temperature become hydrogen-bonded and hydrogen bonds strengthen upon cooling. A detailed knowledge of solution properties enables an optimum tuning of critical parameters such as heating temperature, polymer hydrophobicity, concentration, ionization, etc., which leads to the preparation of desired nano-sized water soluble particles. They are stable over longer periods of time and are stable in the pH range from pH = 4.0 to pH = 9.0.

On the other hand the self-assembly of block copolymers containing a block of a poly(carboxylic acid) and a block of a polymer with strong hydrogen-bond acceptor groups (e.g. poly(ethylene oxide)) leads to pH-sensitive nanoparticles formed by interchain hydrogen bonding between polyacid- and PEO blocks. The particles can be considered as micelles with cores composed of complexed blocks and coronas composed of uncomplexed PEO chains (molecular weight of PEO blocks is chosen to be higher than the molecular weight of the polyacid blocks). The pH-sensitivity of resulting micelles is arising from two effects: pH tunes the hydrophobicity of the polyacid as well as the ionization of carboxylic groups and hence the ability of hydrogen bonding to PEO. The observed micelles are well defined nanoparticles with narrow size distributions (polydispersity R/R 0.05, R is a half width at the half height) comparable with regular diblock copolymer micelles. The micelles are slightly negatively charged. The characterization of solution properties as well as resulting nanoparticles is done by static, dynamic, and electrophoretic light scattering. *Corresponding author: Email: [email protected], Phone: 0042 1557922245, Fax: 0042 1557922245.

93



Overbeek medal award lecture 7

From monolayers to polyelectrolyte multilayer capsules

Helmuth Möhwald*

Department of Interfaces, Max Planck Institute of Colloids and Interfaces, Research Campus Golm, 14424 Potsdam, Germany.

In this award lecture I would like to bridge the areas of colloids and of interfaces which are trivially related, also combined in many names of institutes, groups and journals, but in reality often not seen as one unit. I will do this taking as example my own career which in this area started about 25 years ago. There began a period, largely motivated from biophysics, where one came to a deeper understanding of monolayers from amphiphiles. This was due to the introduction of new methods to resolve the microstructure (Fluorescence and Brewster Angle Microscopy) and nanostructure (Surface X-Ray diffraction, X-Ray-, Neutron-, optical reflec-tion, FTIR spectroscopy). As main results were revealed the existence of phase transitions and separations, coexisting phases with µm sized domains with nonequilibrium shapes, deter-mined by 2D transport, and long range electrostatic interactions effecting peculiar equilibrium shapes. The latter is due to the orientation of molecular dipoles at the interface. The nanos-tructure in turn is distinguished by a zoo of phases in analogy to smectic liquid crystals, and these can be used as measure of local interactions, e.g. protein attachment enzyme hydrolysis or ion binding.

One motivation to study Langmuir monolyers has been the controlled preparation of Langmuir Blodgett films with their promising application in molecular electronics. However, the studies with aliphatic systems revealed that it is very difficult to precisely arrange any functional conjugated system in these. One successful way out has been to give up the high precision (from Å to nm), and prepare multilayers by consecutive adsorption of appositely charged polyelectrolytes. All methods previously established for Langmuir-Blogett films could now be used to demonstrate that these robust and easy to prepare systems are surpris-ingly ordered and well-defined.

Characterization of planar interfaces is limited by the small amount of material at the interface hampering the application of techniques like NMR spectroscopy, ultrafast optical spectroscopy or calorimetry. Therefore it appears logical to coat colloidal particles with their higher specific surface and planar structures. Later dissolving the core we obtain micro- and nanocapsules with walls and surfaces defined with a precision previously established for pla-nar systems. Being able to control surface and internal structure by environmental conditions this also holds for important properties like permeability, shape and mechanics. Thus we have arrived on one side at systems with high application potential which are also important to un-derstand colloidal interactions and at the same time learnt about interfaces, in special their mechanics. As a latest step protein containing amphiphile bilayers have been adsorbed on multilayer capsules, thus yielding a cell biomimetic system thus also bridging materials and bioscience.

*Corresponding author: Email: [email protected], Phone: 0049 3315679201, Fax: 0049 331 5679202.

94



Surface forces and colloidal interactions Keynote lecture 7.2

Direct measurement of critical Casimir forces

Clemens Bechinger*

Fachbereich Physik, University of Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart, Germany.

Similar to electromagnetic vacuum fluctuations which can induce long-ranged interactions between uncharged, conducting surfaces, a rather similar effect was predicted almost 30 years ago to occur in confined binary mixtures close to their critical point. This so-called critical Casimir effect has attracted considerable attention because it can strongly modify the interaction potential of colloidal particles immersed in a binary fluid. We present the first direct measurement of such critical Casimir forces between a colloidal particle and a flat surface in a water – 2,6-lutidine mixture. With total internal reflection microscopy (TIRM) which is capable to resolve forces down to 5fN, we obtain distance resolved particle-wall interaction profiles. Upon approaching the critical point we observe long-ranged interactions which are attractive or repulsive depending on the specific boundary conditions of the walls. This behavior is in good agreement with recent theoretical predictions.

*Corresponding author: [email protected], Phone: 0049 71168565218, Fax: 0049 71168565285.

95



Surface forces and colloidal interactions Contributed lecture 7.2.1

Probing the diffuse layer properties of thiol-covered electrodes by direct force measurements

Samuel Rentsch, Georg Papastavrou*

Department of Inorganic, Applied and Analytical Chemistry, University of Geneva, Geneva, Switzerland.

The diffuse layer properties of modified gold electrodes under potentiostatic control have been determined by direct force measurements. These measurements have been performed with a colloidal probe consisting of a silica particle attached to the cantilever of an atomic force microscope (AFM). The gold electrodes were modified by self-assembled monolayers (SAMs) of different thickness. Additionally, the terminating functional groups of the monolayer have been varied. The interaction force profiles have been fit to the full solutions of the non-linear Poisson-Boltzmann equation. Only by taking into account charge regulation between the surfaces an accurate quantitative description of the force profiles has been obtained. The diffuse layer potentials obtained from these fits were studied in dependence of the potential applied to the gold electrode. The capacitance of the SAM and the potential of zero charge have been determined for various SAMs of different thickness and surface termination. The values obtained by our direct force measurements are in agreement with the ones reported by classical electrochemical techniques. The capacitance of the SAM depends primarily on the thickness of the monolayer and its crystalline structure. Pronounced differences in the potential of zero charge (pzc) for the different functional groups have been found. These changes are related to the dipole moment of the functional group terminating the SAM. Our data are in agreement with ion adsorption, but this effect seems to be less pronounced than for bare gold electrodes.

Fig. 1. a) Schematic representation of the setup for the direct force measurements. b) Interaction force profiles in dependence of the potential applied to the gold electrode.

*Corresponding author: Email: [email protected], Phone: 0041 223796429, Fax: 0041 223796069

96




Hydrodynamic boundary slip at the solid-liquid interface: The roles of surface wettability and roughness

E. Bonaccurso*, S. Guriyanova, B. Semin

Max-Planck-Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany.

The precise knowledge on the dynamics of liquid flow in confined geometries, such as, for example, in microfluidic devices, is a hot topic today. In classical hydrodynamics the no-slip boundary condition (BC) is usually assumed, which means that liquid molecules directly in contact with a solid surface are stationary relative to the solid. However, there is experimental evidence that the no-slip BC is often not applicable in micro- and nanoscale, and slippage of the liquid over the solid is observed [1-3]. The surface wettability is believed to be one of the main factors that influence the occurrence and the magnitude of the slip [4]. It has been recognized that slip occurs on lyophobic surfaces [5]. For a wetted surface, where the interaction between surface and liquid is strongly attractive, no slip is expected. However, some recent experiments have found hints that slip occurs also in completely wetted system, indicating that slip might be a general phenomenon [1,3]. Thus there is a need to redefine the slip and no-slip BCs for various surfaces. Here we present a study of slip dependence on surface wettability using the colloidal probe technique (CPT) to perform thin film drainage measurements of water, and we also discuss the effect of surface roughness. We used bare surfaces like mica and graphite, or used thiol-modified surfaces with contact angles of 15°, 45° and 105°. We demonstrate that surface roughness and surface asperities in the nanometer scale increase the observed slip.

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1. Pit R., Hervet H., Leger L., Phys. Rev. Lett., 2000, 85, 980.2. Craig V., Neto C., Williams D., Phys. Rev. Lett., 2001, 87, 054504.3. Bonaccurso E., Kappl M., Butt H.-J., Phys. Rev. Lett., 2002, 88, 076103. 4. Barrat J.-L., Bocquet L., Phys. Rev. Lett., 1999, 82, 4671.5. Vinogradova O. I., Langmuir, 1995, 11, 2213.6. Bonaccurso E., Butt H.-J., Craig V., Phys. Rev. Lett. 2003, 90, 144501.


97




Effect of geometrical confinement on the structuring of colloidal suspensions:A comparison between theory and experiment

Sabine H. L. Klapp, Dan Qu, Yan Zeng, Regine v. Klitzing*

Stranski-Laboratorium für Physikalische und Theoretische Chemie, Institut für Chemie, TU Berlin, Straße des 17. Juni, 10623 Berlin, Germany.

Small angle neutron scattering experiments at solutions containing Silica particles show a structure peak which indicates interactions between the particles. The position of the structure peak scales with the concentration c with an exponent 1/3. In order to study the effect of geometrical confinement the solutions are confined between a microsphere and a flat interface in a colloidal probe AFM [1]. Oscillatory forces are measured due to layer-by-layer expulsion of the particles. The period has the same value as the particle distance in the corresponding bulk solution calculated from the position of the structure peak [2]. The addition of salt decreases the amplitude, i.e. the ordering of the particles, and the scaling exponent of the particle distance in dependence of the concentration. All results can be perfectly fitted by a theoretical model assuming a DLVO potential. In contrast to this, the confinement of colloidal suspensions between two fluid surfaces in a foam film leads to a constant particle concentration irrespective of the concentration of the former suspension [3].

Fig. 1. Comparison between period dslit in the film of Silica particles and the chain distance of the corresponding bulk solution: comparison between theory and experiment (AFM or SANS).

1. Qu D., Pedersen J. S., Garnier S., Laschewsky A., Möhwald H., v. Klitzing R., Macromolecules 39, 7364.

2. Klapp S. H. L., Qu D., v. Klitzing R., J. Phys. Chem B, 111, 1296. 3. Mauser T., v. Klitzing R., in preparation.

*Corresponding author: Email: [email protected], Tel: 0049 3031423476, Fax: 0049 3031426602.

98




Probing colloidal interactions and stability of a colloid-surfactant mixture by means of

static light scattering, -potential measurements and high turbulent shear

Alessio Zaccone*, Hua Wu, Marco Lattuada, Massimo Morbidelli

Institute for Chemical and Bioengineering, Department of Chemistry and Applied Biosciences, ETH Zurich, 8093 Zurich, Switzerland.

For a model colloidal system composed of polystyrene-acrylonitrile (PSA) particles and potassium stearate (KS) anionic surfactant molecules, its stability in terms of the Fuchs stability ratio, W, has been determined as a function of the surfactant concentration, by measuring the initial aggregation kinetics in the presence of a small amount (15mM) of MgSO4 using the small angle light scattering (SALS) technique. It is found that the stability increases sharply as the KS concentration increases until the saturation of the available surface occurs (Fig.1a). At concentrations higher than 0.10 g/dm3, the W value decreases markedly with KS, as a consequence of attractive depletion forces induced by micelles formation in the water phase (Fig.1a). Adsorption isotherm determined based on the surface tension technique agrees with the W vs KS behaviour, with respect to the onset of saturation and surface-per-molecule, and it can be well described by the two-steps Langmuir isotherm. The first step corresponds to hydrophobic-driven single-molecule adsorption while the second step to associative adsorption of bunches of 4 molecules connected by chain-chain van der Waals forces. The thickness of the KS layer was measured at various KS concentrations by static light scattering (SLS), by fitting the scattering spectrum with the Lorenz-Mie theory for spheres, the diameter of the sphere being the only fitting parameter (Fig. 1b). The first adsorption step (at low KS concentration) does not contribute to the layer’s growth, an observation which can substantiate speculations in the literature about the horizontal configuration of the adsorbed molecule at hydrophobic surfaces. Stability measured under high fluid shear in a turbulent micro-channel (in the absence of screening salt) and -potential measurements fit well into the picture described above. Experiments under shear bring further evidence of significant steric short-range repulsion.

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Fig. 1. a) Fuchs stability ratio (W) as a function of KS concentration. b) The particles diameter as a function of KS concentration from SLS. *Corresponding author: Email:[email protected], Phone : 0041 446334610, Fax: 0041 446321082.

99



Surface forces and colloidal interactions Keynote lecture 7.3

Soft matters in food

Martin E. Leser*, Martin Michel, Laurent Sagalowicz,Pierre A. Aichinger, Heribert J. Watzke

Nestlé Research Center, Vers-Chez-Les-Blanc, CH-1000 Lausanne 26, Switzerland.

Food is the most common soft matter all of us interact with on a daily basis. Food, in order to be eatable, has to be soft, and is therefore ideal to explore concepts originating from soft condensed matter physics, a research field looking at fundamental questions at the boundary between chemistry and physics. Most foods show very complex three-dimensional structures based on molecular interactions, supra-molecular aggregates and colloids controlling to varying degrees, taste, perception, physical properties as well as the dynamics by which different phases of heterogeneous foods are modified and interact with the body. The underlying phenomena can be quite complicated due to the heterogeneity, complex changes in aggregation states as well as a multitude of different time and length scales involved. The biggest challenge in food science is to elucidate the mechanisms allowing to finely tune a foods final properties. Their understanding requires the use of a multidisciplinary approach including physical, chemical, and biological competencies.

In this presentation we will discuss some new examples showing how soft condensed matter physics and surface and colloidal principles can be applied in food science in order to improve food functionality.

*Corresponding author: Email: [email protected], Phone: 0041 217858635; Fax: 0041 21785 85 54.

100




pH induced sol-gel transition in milk investigated by time resolvedmulti-angle static and dynamic light scattering

Christian Moitzi1,*, Hugo Bissig1, Anna Stradner1, Peter Schurtenberger1,2

1Department of Physics, University of Fribourg, Switzerland; 2Fribourg Center for Nanomaterials, University of Fribourg, Switzerland.

The fundamental understanding of food materials has undergone a tremendous improvement during the last two decades, where food science and technology have started to enormously profit from parallel developments in soft matter, materials science and nanotechnology [1]. Food colloids such as casein micelles have been shown to quantitatively follow theoretical descriptions originally developed for colloidal model systems. Moreover, the development of new experimental techniques and their application to complex and dense colloidal food systems has led to a more fundamental understanding of their structural and dynamic properties. Aggregation and gelation of particles in complex fluids represent prime examples where direct links between fundamental research and applications in food sciences can be made. The so-called stability ratio is a particularly important quantity in any attempt to link colloid stability, aggregation kinetics and the underlying interaction potential. Here we describe the use of a novel multi-angle light scattering instrument that implements a 3D cross correlation scheme that allows for time-resolved measurements on turbid suspensions as a convenient method to determine the stability ratio for casein micelles as a function of pH [2]. Multi-angle static and dynamic light scattering has been described as an ideal method for determining the stability ratio for model systems where one can work in highly dilute and correspondingly singly scattering solutions [3]. However, when it comes to industrially relevant systems one often has to deal with concentrations where multiple scattering becomes a problem. Several techniques such as 3D cross correlation have subsequently been introduced to suppress multiply scattered light in turbid solutions and allow for static and dynamic light scattering at high concentrations. Here we demonstrate the application of this instrument for the investigation of the initial stages of casein micelle aggregation in the pH-induced sol-gel transition in skim milk, and we discuss the results using analogies between well-defined model systems in colloid physics and skim milk.

1. Mezzenga R., Schurtenberger P., Burbidge A., Michel M., Nature Materials, 2005, 4, 729. 2. Urban C., Schurtenberger P., Phys. Chem. Chem. Phys., 1999, 1, 3911. 3. Holthoff, H., et al., Langmuir, 1996, 12, 5541.


101




Aggregation of PNIPAM microgels during the coil-globule transition

Andrew M. Howe1,*, Stéphanie Desrousseaux1, Alexander F. Routh2

1Kodak Research Laboratory, 332 Science Park, Milton Road, Cambridge CB4 0WN, UK; 2University of Cambridge, BP Institute (BPI), Madingley Rise, Madingley Road, Cambridge CB3 0EZ, UK.

Aqueous solutions of the cross-linked thermally responsive polymer poly(N-isopropylacrylamide) (pNIPAM) have been studied extensively in recent years [1]. This polymer has been particular well-studied because it has a volume phase transition temperature (VPTT) just below body temperature and is thus thought to have potential bio-medical and cosmetic applications.

Below the VPTT, water is a good solvent for pNIPAM and the polymers in solution behave as soft colloids. At these temperatures, the cross-linked polymer coils swell and, even at concentrations as low as 4% w/w, exhibit viscoelastic behaviour and may form colloidal crystals. In contrast, above the VPTT, water is a poor solvent and the polymer coil collapses to form a globular latex. The volume excluded by these collapsed particles at high temperature is much reduced, and so the suspension viscosity lies close to that of water.At low ionic strength (<10 mM NaCl), the coil-globule transition is thought to proceed without aggregation. However just above the VPTT, when the coils have nearly completely collapsed, there is a jump in both solution viscosity and intensity of scattered light, indicating particle aggregation. The increase in both properties is small and they pass through a maximum over a few C (this contrasts with the behaviour at high ionic strength, when macroscopic gelation occurs and persists over a wide range of temperatures). This behaviour is exhibited even in the absence of added salt and at polymer concentrations down to 0.2% w/w. On cooling, no such unusual behaviour was found and the changes with temperature are monotonic.

Results will be presented for homo-pNIPAM microgels over a range of concentration and with ionic strength below and above the critical aggregation concentration. Data for pNIPAM microgels with 5 mole % acrylic acid, where this weak aggregation also occurs, will be presented as a function of concentration, pH and ionic strength.

The conjecture is that polymer chain entanglement may occur during particle collapse, leading to weak flocculation. The tendency of pNIPAM microgels to aggregate on heating may present significant challenges in applications of these that require complete colloidal stability.

1. Saunders B. R., Vincent B., Adv. Colloid Interface Sci., 1999, 80, 1; Pelton R., Adv. Colloid Interface Sci., 2000, 85, 1.

*Corresponding author: Email: [email protected], Phone: 0044 1223228022 Fax: 0044 1223426202.

102




Polymeric microcapsules: Micromechanics and thermal behaviour

Renate Müller1, Paolo Fernandes1, Andreas Fery2,*

1Max-Planck-Institut für Kolloid- und Grenzflächenforschung, Potsdam, Germany; 2Physikalische Chemie II, Universität Bayreuth, Bayreuth, Germany.

Polymeric microcapsules can be easily prepared by template assisted layer-by-layer assembly or related techniques. Thus various functionalities can be incorporated in the capsule wall or the capsule interior, offering many different possibilities for opening, filling and changing the capsules shape and stability. To understand how mechanical properties are affected, we use a combination of the colloidal probe AFM technique and an inverted optical microscope, see Fig. 1(A); The compliance of individual capsules can be determined and elastic constants of the capsule’s wall material are derived with AFM Force Spectroscopy [1]. We discuss the influence of geometry and temperature [2] (see Fig. 1B) on capsule deformation properties. For microcapsules formed from poly-diallyl-dimethylammonium/polystyrene sulfonate we observe a drastic decrease of the capsules’ compliance during heating, which we explain as transition from a rubbery state into a visco-elastic fluid state [2]. Novel approaches allow producing microcapsules which are gas-filled, we discuss perspectives of these “micro-balloons” and present first results on their deformation behaviour.

Fig. 1. (A) Scheme of the AFM setup, (B) capsules before (left) and after annealing (right).

1. Dubeuil F., Elsner N., Fery A., Eur. Phys. J. E, 2003, 12, 215. 2. Mueller R., Köhler K., Weinkammer R., Sukhorukov G. B., Fery A., Macromolecules,

2005, 38, 9766.


103




Using water-in-oil emulsions for microfabrication

Patrick Mesquida1,*, Macarena Blanco2, Michael Horton2, Steve Nesbitt2

1Department of Mechanical Engineering, King’s College London, United Kingdom, 2Department of Medicine, University College London, United Kingdom.

The integration of “soft” materials with “hard”, silicon-based microtechnology is one of the main challenges in the development of novel biosensors. A key task is to position functional nanoparticles or (bio)-molecules on a selected substrate at sub-100- m accuracy. Here, we present a generic method to position arbitrary, water-soluble nanoparticles/molecules on a variety of flat, solid substrates ranging from different polymer films to SiO2. The nanoparticles/molecules are suspended in an aqueous solution, which, in turn, is dispersed ultrasonically in a non-polar, fluorinated oil. A substrate which is structured with nanometer-scale, electrical charge patterns created by Atomic Force Microscopy-based Charge-Writing (AFM-CW, Fig. 1a) is then immersed in the water-in-oil emulsion (Fig. 1b). The water droplets act as containers for the nanoparticles/molecules and are electrostatically attracted towards the surface charge pattern, where they eventually deposit their cargo in an arrangement geometrically predefined by the pattern (Fig. 1c) [1,2]. We demonstrate the wide applicability of the method with a range of different particles such as silica or metal nanoparticles as well as functional biomolecules. A multiprotein microarray is presented consisting of different antibodies and other proteins on a SiO2 substrate, which could form the basis of novel biosensors [2].

Fig. 1. (a) An electrical charge pattern is created on an electret (insulating) sample. (b) The sample is immersed in a water-in-oil emulsion containing nanoparticles or biomolecules; the droplets deposit their content on the charge pattern. (c) An antibody microarray fabricated by sequential deposition of different proteins on silicon dioxide (1 = rabbit IgG, 2 = BSA-biotin, 3 = mouse IgG, scale bar = 10 m). 1. Mesquida P., Stemmer A., Adv. Mater., 2001, 13, 1395. 2. Blanco E. M., Nesbitt S. A., Horton M. A., Mesquida P., Adv. Mater., 2007, in press. *Corresponding author: Email: [email protected], Phone: 0044 2078482241, Fax: 0044 2078482932.

Documents

· 31 ECIS 2007, 21st Conference of the European Colloid and Interface Society September 10-14, 2007, Geneva, Switzerland Structured surfaces and biointerfaces Contributed lecture