This content has been downloaded from IOPscience. Please scroll down to see the full text.

Download details:

IP Address: 134.197.27.56

This content was downloaded on 19/02/2015 at 19:30

Please note that terms and conditions apply.

Behavior of magnetorheological elastomers with coated particles

View the table of contents for this issue, or go to the journal homepage for more

2015 Smart Mater. Struct. 24 035026

(http://iopscience.iop.org/0964-1726/24/3/035026)

Home Search Collections Journals About Contact us My IOPscience

Behavior of magnetorheological elastomerswith coated particles

Majid Behrooz1, Joko Sutrisno2, Lingyue Zhang1, Alan Fuchs2 andFaramarz Gordaninejad1

1Department of Mechanical Engineering, University of Nevada, Reno, NV 89557, USA2Department of Chemical and Materials Engineering, University of Nevada, Reno, NV 89557, USA

E-mail: faramarz@unr.edu

Received 24 October 2014, revised 23 December 2014Accepted for publication 19 January 2015Published 20 February 2015

AbstractIron particle coating can improve the behavior of magnetorheological elastomers (MREs) byinhibiting iron particle rusting; however, such a process can change physical properties of MREssuch as oxidation resistance, shear modulus, and stiffness change due to an applied magneticfield. In this study, MRE samples are fabricated with regular and polymerized iron particles. Toinvestigate the possibility and extent of these changes, polymerized particle MRE samples aremade using a combination of reversible addition fragmentation chain transfer and clickchemistry. Shear test sample MREs with pure elastomer and 50 wt% MRE with and withoutpolymerization are fabricated. To observe the effect of oxidation on shear properties of MREs,pure elastomer and 50 wt% coated and non-coated samples are oxidized using acceleratedoxidation procedure. Experimental results show that oxidation significantly reduces the shearmodulus of the elastomer matrix. The coating process of iron particles does not significantlychange the shear modulus of resulting MREs but reduces the loss of shear modulus due tooxidation.

Keywords: magnetorheological elastomers, coated particles, shear behavior

(Some figures may appear in colour only in the online journal)

1. Introduction

Magnetorheological elastomer (MRE) is a type of materialwhich is composed of magnetic permeable particles dispersedin an elastomeric medium and show variable mechanicalproperties within a magnetic field. To fabricate MRE, mag-netic particles are added to liquid-state mixture of polymerparts and the resulting mixture is cured either inside or outsideof an external magnetic field resulting in isotropic or direc-tional (orthotropic) MRE, respectively [1, 2]. When particlesare aligned within the magnetic field, chain-like structures ofmagnetic particles are formed and locked in place. Gong et al[3] showed that isotropic MRE does not have a chain-likestructure because it is cured without a magnetic field. Theadvantage of directional MREs is higher stiffness change, ifthe load is applied in the direction of the alignment or per-pendicular to it. Magnetization of directional MRE is higher,when the magnetic field is applied parallel to the direction of

the iron particle chains [4]. Also, higher compressive mod-ulus, thermal conductivity and MR effect are observed foraligned polyurethane MREs [5] compared to homogenousMREs. Researchers have found that MR effect is more pro-nounced for softer elastomer matrix and the storage moduluscan be increased from 400 times [6] to 800% [7], if the off-state shear modulus is low, i.e. in order of kilo Pascal. Davishas theoretically found the optimum particle concentration forincreasing the shear modulus to be 27% by volume [8]. Usingshear tests, it has been shown that MR effect increases athigher frequencies [9] and a normal applied compressive loadcauses a reduction in MR effect during shear deforma-tion [10].

MRE can show stiffness, damping, and hysteresis changewithin a magnetic field; however, damping change is minimalcompared to stiffness change [11]. Such controllable prop-erties can be utilized in vibration isolation applications suchas variable stiffness elements, since MREs have a response

Smart Materials and Structures

Smart Mater. Struct. 24 (2015) 035026 (8pp) doi:10.1088/0964-1726/24/3/035026

0964-1726/15/035026+08$33.00 © 2015 IOP Publishing Ltd Printed in the UK1

time in order of milliseconds [12]. The controllable propertiescan be utilized in variable stiffness and damping devices suchas vehicles’ engine mounts [12], vibration isolator for vehicletransmission system [13], adaptive vehicle seat suspension[14], adaptive tuned vibration absorbers [15, 16], and baseIsolator for building structures [17, 18]. Other researchesproposed soft MRE for air flow controllable valve [19] andadjustable springs in springs in prosthetic devices [20]. Thereis also limited work for modeling MRE behavior and it posesits own challenges since MRE shows non-linear viscoelasticbehavior which is affected by magnetic field and loadingfrequency. A model is presented by Shen et al [21] for pre-dicting the stress strain behavior of MREs within magneticfield as well as phenomenological models based on Ramberg-Osgood [22] and Bouc–Wen model [11].

In MREs iron particles are embedded in an elastomericmedium and are not exposed to air; however, the moisture andoxygen can penetrate with time and alter the properties ofelastomeric matrix or the bonding between the matrix and theparticles. Also, the hygrothermal effects may reduce thestrength of the bonds among iron particles and the elastomericmatrix or may affect the elastomeric matrix itself. It is shownthat oxidation can significantly reduce the stability of naturalrubber based MREs and higher oxidation rates are observedfor MREs containing larger percentage of iron particles [23].To prevent the oxidation of iron particles and hence increasethe durability of the MREs, iron particles can be coated withdifferent techniques including reversible addition fragmenta-tion chain transfer (RAFT) and click chemistry.

However coating may change mechanical, electrical, andmagnetic properties of MREs that need to be investigatedfurther. Coating carbonyl iron particles with Polypyrroleribbons has other advantages such as improving sedimenta-tion properties of MR fluid [24]. Also, coating particles ofMR fluid with a layer of polysiloxanes can increase the oxi-dation and chemical stability [25]. It is shown that coatingwith poly methyl methacrylate can increase the shear modulusover 200%, and thus, reduce the relative MR effect [26]; butLauryl Sodium Sulfate (SDS) and Sorbitan Monooleate (Span80) as a coating layer have reduced the base shear modulusand increased the relative MR effect [27]. Compression testresults have shown that polymerized iron particle MREs havehigher oxidation stability [28]. The combination of RAFT andclick chemistry reactions for surface polymerization of ironparticles has been studied by Yuan et al [29]. Moreover, it isshown that coating particles reduces the magnetizationsaturation point [30]. Although previous studies have inves-tigated the effect of particle coating on magnetization ofparticles and changes in properties of MRF, only a few stu-dies have been performed on the effect of coating onmechanical properties on MRE.

In this research, particles of 50 wt% MRE samples arecoated utilizing a combination of RAFT and click chemistrymethods. To investigate the effect of coating on the perfor-mance of MREs, ASTM standard double lap shear samplesare fabricated for pure elastomer, 50 wt% coated, and 50 wt%non-coated iron particles. MRE samples are oxidized using anaccelerated heat chamber. Shear experiments are performed to

investigate the effect of coating and oxidation on MREsamples. Results show that oxidation reduces the off-stateshear stiffness of the MREs and hence increases the relativestiffness changes due to magnetic field. Finally coating of ironparticles does not significantly change the shear modulus, butprotects the MREs by reducing the loss of stiffness due tooxidation.

2. Coated and non-coated particle MRE samples

2.1. Surface coating mechanism of iron particle via clickchemistry

Polymer coating on iron particle surface can enhance bothchemical and physical performances of MRE. A RAFTtechnique is employed to graft the polymers. Since the surfacecoating materials are non-magnetizable, they do not affect themagnetic field while they improve the endurance of MRE. Itis shown that 20 wt% polymer coating on the iron particlessurface decreases the magnetic saturation about 5% in com-pared with pristine iron particles [31]. The effect of coating onthe magnetic saturation of iron particles may be negligiblebecause the thickness of coating is in nanometer scale andmass percentage of polymer coating is lower than previouslyreported [31]. RAFT method offers a narrow polydispersityindex which means polymer has uniform molecular weight[32–38] polymer can be covalently bonded to the substrate.

To coat the iron particles, the substrate should be func-tionalized using azide, and the tandem molecule is functio-nalized using alkyne group in order to react through clickchemistry. Copper (II) sulfate is reduced in the presence ofsodium ascorbate, which becomes Cu (I), denoted as[LnCu]+. In click chemistry, the ligand (Ln) can be the sol-vent, such as acetonitrile, and water [35]. The reduced copper/Ln reacts with alkyne group and this is followed by interac-tion with nitrogen from azide group. Finally, the reactionbetween the alkyne and azide functional groups yields a ringclosed triazole group.

In this process, 0.5 g of azide modified iron particles wasadded into a glass vial and followed by adding poly(tetra-fluoropropyl methacrylate, MW 200.13 g mol−1 [39]) (0.5 g)CuSO4 (6.65 mg), sodium ascorbate (241 mg) and dimethyl-formamide (DMF) (2 mL). The mixture was sonicated for5 min and continuously stirred in oil bath at 70 °C for 18 h.The conjugated poly(tetrafluoropropyl methacrylate)/ironparticles were filtered, and washed using DMF several timeswith toluene consecutively. Then, the poly(tetrafluoropropylmethacrylate) coated iron particles were dried in a vacuumoven at 50 °C for 24 h.

Initially, iron particles were functionalized with 2-4(-chlorosulfonylphenyl)-ethytrichlorosilane in toluene. Theparticles were washed using distilled water and ethanol,consecutively, and dried in vacuum oven [28]. Surface initi-ated iron particles were then reacted with sodium azide inDMF to provide azide terminated particles which would bereacted with alkyne through click chemistry reaction [40]. 3-benzylsulfanylthiocarbonylsufanyl-propionic acid as chain

2

Smart Mater. Struct. 24 (2015) 035026 M Behrooz et al

transfer agent (CTA) was synthesized according to thereported literature [41]. The synthesized CTA was modifiedwith propargyl alcohol to provide alkyne group [40]. Thealkyne terminated CTA was used to polymerize tetra-fluoropropyl methacrylate monomer. This reaction resulted inalkyne functionalized poly(tetrafluoropropyl methacrylate).The mechanism of surface coating of iron particles poly(tet-rafluoropropyl methacrylate) through a combination of RAFTand click chemistry is shown in figure 1.

The chemical analysis and surface morphologies of graf-ted poly(tetrafluoropropyl methacrylate)–iron particles was

characterized using Hitachi S-4700 equipped with an OxfordEDS System. The samples were magnified from 800X to35 000X at an accelerating potential of 20 kV. The SEMimages of non- and surface coated iron particles are shown infigures 2(a) and (b), respectively. Thin and uniform graftedpolymers on a single iron particle can be seen in these pictures.

2.2. MRE Fabrication

For this research pure rubber samples, 50 wt% coated andnon-coated Silicone MREs were prepared. Silicone QM113A

Figure 1. The mechanism of surface coating of iron particles poly(tetrafluoropropyl methacrylate) through a combination of reversibleaddition fragmentation chain transfer (RAFT) and click chemistry.

3

Smart Mater. Struct. 24 (2015) 035026 M Behrooz et al

and B (Quantum Silicones) with the hardness of sevendurometer were used for elastomer matrix and carbonyl ironpowder CN (3–7 microns, BASF) with a density of 3.5(g cm−3) was used as iron particles. The two components weremixed with a mixer for 7 min at a weight ratio 10:1. Then,iron particles were added at the desired weight percentage,mixed, and the resulting mixture is poured into the mold.Then, the polymer was degassed at 25 in Hg vacuum for30 min to remove the bubbles, and cured under 1.0 T ofmagnetic flux density for 5 h at 70 °C to align the iron par-ticles. The curing process was continued in the oven at 70 °Cfor 12 h. The shear samples were fabricated based on theASTM standard [42]. The electromagnet with the shearsample mold is shown in figure 3(a) and the shear MRE moldis shown in figure 3(b). The MRE mold is capable of curing12 samples at a time. The picture of silicone MRE samples isshown in figure 4(a) and a silicone MRE double lap shear testis shown in figure 4(b). Sil-Poxy silicon adhesive was usedand cured for 12 h to bond MREs and steel bars. The surfaceof steel bars were roughened using 220 grit sandpaper.

2.3. Oxidation of MREs

Elastomer matrix and MRE samples were exposed to air atroom temperature for one week after they were removed fromthe mold prior to oxidation. Rectangular shape elastomer

matrix and MRE samples were placed on three aluminumracks and the position of each sample was marked. The rackswere placed into the chamber and the chamber was sealed.Compressed air was added to the chamber until the pressurereached 100 psi. The thermo-controller was set to 100 °C.When the temperature stabilized at 100 °C, the pressure wasadjusted back to 0.68MPa. The samples were taken out afterone weeks. The oxidative test procedure for the MRE samples

Figure 2. SEM images of (a) non-coated and (b) coated iron particle.

Figure 3. Electromagnet for curing MREs and the mold inside.

Figure 4. room temperature vulcanization (RTV) siliconeMRE (a)shear samples and (b) shear specimen, for shear test.

4

Smart Mater. Struct. 24 (2015) 035026 M Behrooz et al

with polymer coated iron particles was treated, similarly. Theaccelerated aging chamber is shown in figure 5.

3. Shear experiments

Shear properties of MREs can be examined using a quasi-static shear experiment. To correlate the input electric currentwith the magnetic field inside MRE samples, the magneticfield is measured using a magnetometer. As shown infigure 6(a) the probe of the magnetometer is inserted in asmall slit inside the sample and the electric current is changedto measure the magnetic field of different samples. The actualmagnetic field inside MREs is expected to be a little highersince the slit is expected to reduce the flux density.

Figure 6(b) demonstrates the magnetic field which is stronglyrelated to the iron particle concentration and does not changeconsiderably with the oxidation of the samples. For coatedparticles the magnetic field is 9.35% lower on average sincethe coating layer occupies space and reduces the amount ofiron particles per unit volume. In the case of the pure elas-tomer samples, there is 150 mT magnetic flux density at5 amp; but as it is shown in figure 8, the effect of magneticfield, when iron particles are not present, is minimal.

To investigate the effect of coating and oxidation onMRE samples, double lap shear tests are performed on anInstron electromechanical testing system (model 4210), asshown in figure 7. Shear test setup is consisted of two thicksteel plates, and an electromagnet that can generate a closed-loop magnetic field, when the sample is installed. Shear testspecimens are bolted to the Instron actuator and the shear testsetup. All parts are parallel to ensure pure shear test condition.A 500lbf Lebow load cell (model number 3132-500) and aRDP Electronics LVDT (model number DCTH100AG) dc todc displacement transducer with ±2.5 mm range and1494 mVmm−1 is used to measure force and displacement,respectively.

Figure 5. High pressure reactor for MRE ageing.

Figure 6. (a) Magnetic flux density measurement test set up and (b) magnetic flux density for different samples at different amps.

Figure 7. Double lap shear test setup and INSTRON dynamic testingsystem.

5

Smart Mater. Struct. 24 (2015) 035026 M Behrooz et al

Shear experiments are performed on pure elastomer and50 wt% coated and non-coated samples with the input fre-quency of 0.1 Hz and 17.5% strain amplitude. The inputelectric current is increased from zero to 4 amp to observe theeffect of induced magnetic field within MREs. The appliedmagnetic field within MREs is parallel with the iron particlechains to achieve highest possible MR effect. Each test hasbeen performed four times to ensure the consistency of theresults and to obtain the standard deviation. Figure 8(a)demonstrates shear test results of the pure elastomer samples.As can be seen, the magnetic field does not affect the shear testresults. As shown in figure 8(b), oxidation for a period of oneweek significantly reduces the shear modulus of the elastomer.

Figure 9 shows the stress–strain loop of the shear MREsamples with 50 wt% non-coated particle concentration. Ascan be seen, by increasing the input electric current themaximum stress in the loop increases, which corresponds toincrease in the stiffness. However, area of the loop staysalmost unchanged; thus, the change in the damping is mini-mal. On the other hand, since the base stiffness decreases afteroxidation, then the relative change of the stiffness increases.This occurs since the stiffness change remains constant, butthe off-state stiffness is reduced.

Figure 10 shows similar results for MREs with 50 wt%coated particles. Comparing the two Figures shows that the

off-state stiffness does not change with coating of the ironparticles, but after oxidation the off-state stiffness is lessreduced as compared to the non-coated particles. This sug-gests that the coating preserves the stiffness better underoxidation.

The effective shear modulus helps to understand the MReffect under polymerization. The effective shear modulus isobtained based on maximum strain and maximum stress [43].The MR effect is calculated using equation (1). MR effect forpure elastomer and 50 wt%. coated and non-coated MRE ispresented in table 1 along with the standard deviation of theeffective shear modulus. As can be seen from table 1, oxi-dized coated samples tend to preserve the MRE propertiescompared to non-coated samples.

×−

=G G

GMR effect 100 (1)on off

off

4. Summary and conclusions

In this study iron particles are polymerized using a combi-nation of RAFT and click chemistry techniques. Shear MREsamples are prepared based on the ASTM standard using

Figure 8. Pure elastomer (a) without oxidation and (b) after one week of oxidation.

Figure 9. Stress–strain results for 50 wt% non-coated MRE samples (a) without oxidation and (b) after one week of oxidation.

6

Smart Mater. Struct. 24 (2015) 035026 M Behrooz et al

coated and non-coated particles. Some MRE samples areoxidized and their shear properties are examined utilizingdouble-lap shear tests to observe the effect of coating onperformance of MREs.

Results show that oxidation significantly reduces theshear modulus of the pure elastomer as well as the MREs. Theshear modulus of the pure elastomer is reduced three timeswhile shear modulus of non-coated MREs is reduced nearlyfour times. This demonstrates that oxidation mainly affectsthe elastomer matrix, and also affects the bonding amongparticles and the matrix. It is shown that the effective modulusof coated MREs reduces 2.3 times, and that coating particlespreserves the stiffness of MREs in oxidative environments.

Acknowledgments

This work was supported by the US National Science Foun-dation. The authors are grateful for the support.

References

[1] Fuchs A, Zhang Q, Elkins J, Gordaninejad F and Evrensel C2007 Development and characterization ofmagnetorheological elastomers J. Appl. Polym. Sci. 1052497–508

[2] Carlson J D and Jolly M R 2000 MR fluid, foam and elastomerdevices Mechatronics 10 555–69

[3] Gong X, Zhang X and Zhang P 2005 Fabrication andcharacterization of isotropic magnetorheological elastomersPolym. Test. 24 669–76

[4] Ginder J M, Nichols M E, Elie L D and Tardiff J L 1999Magnetorheological elastomers: properties and applicationsProc. SPIE 3675 131

[5] Wu J, Gong X, Fan Y and Xia H 2010 Anisotropicpolyurethane magnetorheological elastomer preparedthrough in situ polycondensation under a magnetic fieldSmart Mater. Struct. 19 105007

[6] Chertovich A V, Stepanov G V, Kramarenko E Y andKhokhlov A R 2010 New composite elastomers with giantmagnetic response Macromol. Mater. Eng. 295 336–41

Figure 10. Stress–strain results for 50 wt% coated MRE samples (a) without oxidation and (b) after one week of oxidation.

Table 1. Effective shear modulus and percentage of MR effect.

Input current (A) Effective shear’s modulus (kPa) Standard deviation MR effect (%)

Non-oxidized 0 152.6 1.210 wt% 2 153.6 0.65 0.6

4 156.9 2.32 2.8Oxidized 0 51.5 0.8

2 51.6 0.32 0.24 51.7 0.26 0.4

Non-oxidized 0 342.9 7.3750 wt% Coated 2 365.7 7.12 6.7

4 374.3 5.41 9.2Oxidized 0 145.7 1.35

2 171.4 2.11 17.64 182.9 2.47 25.5

Non-oxidized 0 365.7 6.67Non-coated 2 388.6 5.42 6.2

4 422.9 6.22 15.6Oxidized 0 94.3 1.17

2 134.3 1.54 42.44 168.6 2.17 78.8

7

Smart Mater. Struct. 24 (2015) 035026 M Behrooz et al

[7] Gong X L, Chen L and Li J F 2007 Study of utilizablemagnetorheological elastomers Int. J. Mod. Phys. B 214875–82

[8] Davis L C 1999 Model of magnetorheological elastomersJ. Appl. Phys. 85 3348

[9] Jung H-J, Lee S-J, Jang D-D, Kim I-H, Koo J-H and Khan F2009 Dynamic characterization of magneto-rheologicalelastomers in shear mode IEEE Trans. Magn. 453930–3

[10] Dong X, Ma N, Qi M, Li J, Chen R and Ou J 2012 Thepressure-dependent MR effect of magnetorheologicalelastomers Smart Mater. Struct. 21 075014

[11] Behrooz M, Wang X and Gordaninejad F 2013 Modeling of anew magnetorheological elastomer-based isolator Proc.SPIE 8688 86880Z

[12] Ginder J M, Nichols M E, Elie L D and Clark S M 2000Controllable-stiffness components based onmagnetorheological elastomers Proc. SPIE 3985418–25

[13] Hoang N, Zhang N and Du H 2011 An adaptive tunablevibration absorber using a new magnetorheologicalelastomer for vehicular powertrain transient vibrationreduction Smart Mater. Struct. 20 015019

[14] Du H, Li W and Zhang N 2011 Semi-active variable stiffnessvibration control of vehicle seat suspension using an MRelastomer isolator Smart Mater. Struct. 20 105003

[15] Deng H, Gong X and Wang L 2006 Development of anadaptive tuned vibration absorber with magnetorheologicalelastomer Smart Mater. Struct. 15 N111–6

[16] Deng H and Gong X 2008 Application of magnetorheologicalelastomer to vibration absorber Commun. Nonlinear Sci.Numer. Simul. 13 1938–47

[17] Behrooz M, Wang X and Gordaninejad F 2012 Control ofstructures featuring a new MRE isolator system Proc. SPIE8341 83411I

[18] Eem S H, Jung H J and Koo J H 2013 Seismic performanceevaluation of an MR elastomer-based smart base isolationsystem using real-time hybrid simulation Smart Mater.Struct. 22 055003

[19] Böse H, Rabindranath R and Ehrlich J 2012 Softmagnetorheological elastomers as new actuators for valvesJ. Intell. Mater. Syst. Struct. 23 989–94

[20] Guðmundsson Í 2011 A Feasibility Study ofMagnetorheological Elastomers for a Potential Applicationin Prosthetic Devices (Reykjavik: University of Iceland)

[21] Shen Y, Golnaraghi M F and Heppler G R 2004 Experimentalresearch and modeling of magnetorheological elastomersJ. Intell. Mater. Syst. Struct. 15 27–35

[22] Eem S-H, Jung H-J and Koo J-H 2012 Modeling of magneto-rheological elastomers for harmonic shear deformation IEEETrans. Magn. 48 3080–3

[23] Lokander M, Reitberger T and Stenberg B 2004 Oxidation ofnatural rubber-based magnetorheological elastomers Polym.Degrad. Stab. 86 467–71

[24] Mrlik M, Sedlacik M, Pavlinek V, Peer P, Filip P and Saha P2013 Magnetorheology of carbonyl iron particles coatedwith polypyrrole ribbons: the steady shear study J. Phys.Conf. Ser. 412 012016

[25] Sedlacik M, Pavlinek V, Vyroubal R, Peer P and Filip P 2013A dimorphic magnetorheological fluid with improvedoxidation and chemical stability under oscillatory shearSmart Mater. Struct. 22 035011

[26] Li J, Gong X, Zhu H and Jiang W 2009 Influence of particlecoating on dynamic mechanical behaviors ofmagnetorheological elastomers Polym. Test. 28 331–7

[27] Jiang W, Yao J, Gong X and Chen L 2008 Enhancement inmagnetorheological effect of magnetorheological elastomersby surface modification of iron particles Chin. J. Chem.Phys. 21 87–92

[28] Fuchs A, Sutrisno J, Gordaninejad F, Caglar M B and Liu Y 2010Surface polymerization of iron particles for magnetorheologicalelastomers J. Appl. Polym. Sci. 117 934–42

[29] Yuan K, Li Z-F, LÜ L-L and Shi X-N 2007 Synthesis andcharacterization of well-defined polymer brushes graftedfrom silicon surface via surface reversible addition–fragmentation chain transfer (RAFT) polymerization Mater.Lett. 61 2033–6

[30] Pu H, Jiang F, Wang Y and Yan B 2010 Soft magneticcomposite particles of reduced iron coated with poly(p-xylylene) via chemical vapor deposition polymerizationColloids Surf. A 361 62–5

[31] You J L, Park B J, Choi H J, Choi S B and Jhon M S 2007Preparation and magnetorheological characterization of CI/PVB core/shell particle suspended MR fluids Int. J. Mod.Phys. B 21 4996–5002

[32] Hu B, Fuchs A, Huseyin S, Gordaninejad F and Evrensel C2006 Supramolecular magnetorheological polymer gelsJ. Appl. Polym. Sci. 100 2464–79

[33] Rowe-Konopacki M D and Boyes S G 2007 Synthesis ofsurface initiated diblock copolymer brushes from flat siliconsubstrates utilizing the RAFT polymerization techniqueMacromolecules 40 879–88

[34] Odian G G 2004 Principles of Polymerization (Hoboken, NJ:Wiley)

[35] Huang Y, Liu Q, Zhou X, Perrier S and Zhao Y 2009 Synthesisof silica particles grafted with well-defined living polymericchains by combination of RAFT polymerization andcoupling reaction Macromolecules 42 5509–17

[36] Moad G, Rizzardo E and Thang S H 2006 Living radicalpolymerization by the RAFT process—a first update Aust. J.Chem. 59 669–92

[37] Zhu J, Zhu X, Kang E T and Neoh K G 2007 Design andsynthesis of star polymers with hetero-arms by thecombination of controlled radical polymerizations and clickchemistry Polymer 48 6992–9

[38] Hua D, Tang J, Cheng J, Deng W and Zhu X 2008 A novelmethod of controlled grafting modification of chitosan viaRAFT polymerization using chitosan-RAFT agentCarbohydr. Polym. 73 98–104

[39] www.sigmaaldrich.com/catalog/product/aldrich/371998?lang=en&region=US

[40] Ranjan R and Brittain W J 2007 Combination of living radicalpolymerization and click chemistry for surface modificationMacromolecules 40 6217–23

[41] Stenzel M H and Davis T P 2002 Star polymer synthesis usingtrithiocarbonate functional β-cyclodextrin cores (reversibleaddition–fragmentation chain-transfer polymerization)J. Polym. Sci. A 40 4498–512

[42] D11 Committee 2012 Test Methods for Rubber Properties inCompression or Shear (Mechanical Oscillograph) (ASTMInternational) D945

[43] Li Y, Li J, Li W and Samali B 2013 Development andcharacterization of a magnetorheological elastomer basedadaptive seismic isolator Smart Mater. Struct. 22 035005

8

Smart Mater. Struct. 24 (2015) 035026 M Behrooz et al