CompositesAnd

Nanochemistry

Lecture 15

Nanomaterial reinforcement in composites

Nanofibers in use

• Processing them into various matrices follow earlier compositedevelopments such as

- Polymer compounding- Producing filled polymers- Assembly of laminate composites- Polymerizing rigid rod polymers

• Purpose- Replace existing materials where properties can be superior- Applications where traditionally composites were not a

candidate

Nano-reinforced composites

• Nanotechnology provides new opportunities for radical changesin composite functionality

• Major benefit is to reach percolation threshold at low volumes(< 1%) when mixing nanoparticles in a host matrix

• Functionalities can be added when we control the orientation of the nanoscale reinforcement.

Benefits of nanotech for composites

• This always implies “structure +” since in most cases the majorfunction of a structure is to carry load or provide shape. Additional functions can be:

• Actuation controlling position, shape or load

• Electrical either insulate or conduct

• Thermal either insulate or conduct

• Health monitor, control

• Stealth managing electromagnetic or visible signature

• Self-healing repair localized damage

• Sensing physical, chemical variables NRC Report, 2003

Multifunctionality in materials

• Building in additional functionalities into load-bearing structuresis one key example:

- Sensing function* Strain* Pressure* Temperature* Chemical change* Contaminant presence

• Miniaturized sensors can be embedded in a distributed fashion to add “smartness” or multifunctionality. This approach is ‘pre-nano’ era.

• Nanotechnology, in contrast, is expected to help in assembling materials with such functional capabilities

Multifunctional materials: sensing

• Possible, in principle, to design any number of composites with multiple levelsof functionality (3, 4, 5…) by using both multifunctional matrices and multifunctional reinforcement additives

- Add a capsule into the matrix that contains a nanomaterial sensitive to thermal, mechanical, electrical stress; when this breaks, would indicate the area of damage

- Another capsule can contain a healant

- Microcellular structural foam in the matrix may be radar-absorbing,conducting or light-emitting

- Photovoltaic military uniform also containing Kevlar for protectiongenerate power during sunlight for charging the batteries of

various devices in the soldier-gearNRC Report, 2003

Examples of multifunctional materials

• Carbon nanotubes, nanofibers

• Polymer clay nanocomposites

• Polymer cross-linked aerogels

• Biomimetric hybrids

Expectations:- ‘Designer’ properties, programmable materials- High strength, low weight- Low failure rates- Reduced life cycle costs

Composite materials

‘Self-healing plastic’ by Prof. Scott White (U. of Illinois) Nature (Feb. 15, 2001)

• Plastic components break because of mechanical or thermalfatigue. Small cracks and large cracks: catastrophic failure.‘Self-healing’ is a way of repairing these cracks without humanintervention.

• Self-healing plastics have small capsules that release a healingagent when a crack forms. The agent travels to the crack through capillaries similar to blood flow to a wound.

• Polymerization is initiated when the agent comes into contactwith a catalyst embedded in the plastic. The chemical reactionforms a polymer to repair the broken edges of the plastic. New bond is complete in an hour at room temperature.

A self-healing material

• Frequently encountered powders:- Cement, fertilizer, face powder, table salt, sugar, detergents, coffee

creamer, baking soda…

• Some products in which powder incorporation is not obvious- Paint, tooth paste, lipstick, mascara, chewing gum, magnetic recording

media, slick magazine covers, floor coverings, automobile tires…

• For most applications, there is an optimum particle size- Taste of peanut butter is affected by particle size- Extremely fine amorphous silica is added to control the ketchup flow- Medical tablets dissolve in our system at a rate controlled by particle size- Pigment size controls the saturation and brilliance of paints- Effectiveness of odor removers is controlled by the surface area of

adsorbents.

From: Analytical methods in Fine Particle Technology, Webb and Orr

Fine Particle Technology

• Adding certain inorganic clays to rubber dramatically improves the lifetime and wear-characteristics of tires.

Why ?

The nanoscale clay particles bind to the ends of the polymer molecules - which you can think of as molecular strings - and prevent them from unraveling.

Fine Particles 2

Reactions of shaped carbons

Detection

Reactions

The electron microscope

Electron Microscopy and tube wall measurements

Raman vibrational modes in SWNTs

0 200 1200 1400 1600 1800 2000-2000

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A. Hirsch, Angew. Chem. Int. Ed., 41 (2002) 1853.

Chemistry

The main approaches for the modification of these quasione-dimensional structures can be grouped into three categories:(a) the covalent attachment of chemical groupsthrough reactions onto the ð-conjugated skeleton of CNT;(b) the noncovalent adsorption or wrapping of variousfunctional molecules; and (c) the endohedral filling of theirinner empty cavity.

SWCNT chemistry

Chem Rev, 106 (2006) 1105

Functionalisation of CNTs: Prato reagent

CNT-Polymer mixtures

Nanotubes – different scale lengths

The Space Elevator

Application of f-CNTs in Medicine/Pharmacy

Antifungal activity of AmB conjugated to carbon nanotubes (CNT 2). Candida parapsilosis (black bar); Candida Albicans (dashed bar); Cryptococcus neoformans (grey bar).

Confocal microscopy images of 3T6 cells incubated with fluorescent CNT

f-CNT penetrated into the cells

C. Klumpp et al. / Biochimica et Biophysica Acta 1758 (2006) 404– 412