STUDY OF THERMOMECHANICAL EFFECTS OF MAIN CHAIN LIQUID CRYSTAL ELASTOMER AS FUNCTION OF CROSSLINKER CONCENTRATION. Thermomechanical effects of dry Main Chain Liquid Crystal Elastomer (MCLCE) with the different concentration of crosslinker 8 %, 12 %, 14% and 16% have been studied. Length of MCLCE monotonically shrinks parallel to the director, while it expands perpendicularly to the director, with a somewhat faster change at nematic isotropic transition phase, Tni. The result of the investigation showed that the value of maximum contraction is greater and faster than maximum expansion

Farikhah, Irna

Yusuf, Yusril

Jusami | Indonesian Journal of Materials Science

Jurnal Sains Materi IndonesiaIndonesian Journal of Materials ScienceVol. 12, No. 2,Februari 2011, hal : 134 - 136ISSN : 1411-1098134Akreditasi LIPI Nomor : 452/D/2010Tanggal 6 Mei 2010STUDY OF THERMOMECHANICAL EFFECTSOF MAIN CHAIN LIQUID CRYSTAL ELASTOMERAS FUNCTION OF CROSSLINKER CONCENTRATIONIrna Farikhah1,2 andYusrilYusuf11Department of Physics, Faculty of Mathematics and Natural Sciences-Gadjah Mada UniversitySekip Utara, BLS 21, Bulaksumur, Yogyakarta 55281, Indonesia2Department of Physics, Faculty of Mathematics and Natural Sciences-IKIP PGRI SemarangSidodadi Timur 24, Semarang 55125, Indonesiae-mail : irnafarikhah@yahoo.co.idABSTRACTSTUDY OF THERMOMECHANICAL EFFECTS OF MAIN CHAIN LIQUID CRYSTALELASTOMER AS FUNCTION OF CROSSLINKER CONCENTRATION. Thermomechanical effects ofdry Main Chain Liquid Crystal Elastomer (MCLCE) with the different concentration of crosslinker 8 %, 12 %,14% and 16% have been studied. Length of MCLCE monotonically shrinks parallel to the director, while itexpands perpendicularly to the director, with a somewhat faster change at nematic isotropic transition phase,Tni. The result of the investigation showed that the value of maximum contraction is greater and faster thanmaximum expansion.Key words : Main Chain Liquid Crystal Elastomers (MCLCE), Thermomechanical effects, Function ofcrosslinker concentrationABSTRAKSTUDI EFEKTERMOMEKANIK RANTAIUTAMADARI ELASTOMERKRISTALCAIRSEBAGAI FUNGSI KONSENTRASI CROSSLINKER. Efek termomekanik dari rantai utama padaelastomer kristal cair kering (MCLCE) dengan konsentrasi crosslinker yang berbeda pada 8 %, 12 %, 14 % dan16 % telah dipelajari. Panjang dari MCLCE secara monoton memendek paralel terhadap director, namunmemanjang secara tegak lurus terhadap director, dengan perubahan yang cepat pada fasa transisi nematicisotropic (Tni). Hasil dari penelitian ini menunjukkan bahwa nilai kontraksi maksimal lebih besar dan lebihcepat dari ekspansi maksimal.Kata kunci : Main Chain Liquid Crystal Elastomers (MCLCE), Efek termomekanik, Fungsi konsentrasi crosslinkerINTRODUCTIONThe invention of Liquid Crystal (LC) by FriedrichReinitzer in 1888 had improved the research of itsproperties. Some properties of LC had been investigatedespecially in molecular structure and electrical responseof LC. It was not until the early 1970s that the successfulcommercialization of a pocket calculator with a displayof device that utilized liquid crystals sparked an intenseinterest in the field [1].In the last twenty years, the interest of LChas blossomed and incorporated with varied material.In this point, Liquid Crystal Elastomers (LCE)was developed and improved, which LC is a uniquematerial with special properties combination LCand rubber properties. The elastic properties of LCEmade it very potential to be developed as artificialmuscles [1 ,2].LCE was synthesized first by Finkelmann at1981 and had been improved until the invention of MainChain Liquid Crystal Elastomer (MCLCE) [2,3].Polydomain Side Chain Liquid Crystal Elastomer (SCLCE)was the first LCE which was invented and thendeveloped to be monodomain SCLCE. After theinvention of SCLCE, the research of LCE was growinguntil the discovery of monodomain MCLCE [4].As early as 1975, De Gennes predictedqualitatively the extraordinary mechanical and opticalproperties that should be expected from nematicMCLCE, where the mesogenic units are connectedStudy of Thermomechanical Effects of Main Chain Liquid Crystal Elastomer Liquid Crystal Elastomer as Function ofCrosslinker Concentration (Irna Farikhah)135within the polymer backbone to build up the polymernetwork [5].One of the most outstanding features of nematicelastomers is a reversible change in length at the nematicto isotropic phase transformation for monodomainsamples that are macroscopically ordered with respectto the director. This charge in shape is due to the couplingof the liquid crystalline order with the polymer chainconformation of the network. The coupling has beeninvestigated in detail for SCLCE [6,7], where themesogenic moieties are attached as side groups to themonomer units of the network. However, only fewinvestigations have been performed on main 56 chainelastomers [8].There had been substantial research on theSCLCE. Based on result, the effects of SCLCE wasstill relatively small so that we need another type ofLCE in order to obtain the larger effects to be appliedon artificial muscle. MC LCE is one of the LCE type thathas been predicted to be more appropriate to be appliedas artificial muscle.EXPERIMENTAL METHODThe polydomain MCLCE was synthesized ina one-step reaction, by dissolving the monomer2-ethyl-1,4-phenylen bis [4-[4-(vinyloxil) buboxy]benzoate] (C34H38O6) and 8 %, 12 %, 14 % and 16 %,the chain extender 1,1,3,3,-tetramethyldisiloxane(C14H14OSi2). Monodomain MCLCE was prepared inthree types crosslinking concentration, 8 %mol,12 %mol, 14 %mol and 16 %mol of the crosslinkingagent pentamethylcyclopentasiloxane (C5H20O5Si5)in toluene. The monodomain MCLCE was obtainedby mechanical stretching in order to obtainthe uniform director orientation, nˆ, parallel to thestretching direction.To measure the length changes of LSCEduring the variation of temperature, we prepared typeof rectangular LSCE sample that is slicing parallelto nˆ (planar sample). The sample is observed by amicroscope (Nikon) equipped with a temperaturecontroller. The image of each temperaturephotographed during the heating and cooling processeswith a range between 30 oC until 120 oC for8 %mol, 12 %mol, 14 %mol and 16 %mol of thecrosslinking agent.MCLCE samples were placed in glass.Samples are monodomain MCLCE. Monodomainplanar MCLCE was obtained from cutting sampleparallel with the director, n. A polarizing microscopewas used to observe the thermo-mechanicaleffects which linked to a CCD camera and a PC (PersonalComputer). CCD camera was used to take the picture ofthermomechanical effects and the picture was savedin the PC.RESULTS AND DISCUSSIONFigure 1 shows the observation ofthermomechanical effects of MCLCE with 8 %, 12 %,14 % and 16 % cross linking concentrations, throughheating and cooling.The anisotropic thermomechanical effects forMCLCE samples during the heating and the coolingFigure 1. Thermo-mechanical effect induced shapechanges of MCLCE for planar samples. MCLCEs shrinkon heating and expand on cooling (parallel the director),║n. In contrast, MCLCEs expand n on heating andshrink on coolingFigure 2. Temperature dependence of the relative lengthchanges, x║n and yn for dry MCLCE-8, MCLCE-12,MCLCE-14 and MCLCE-16 samples during the heatingand the cooling processes. The drastic length changesare observed at Tc (TniMCLCE-8 ~84oC, TniMCLCE-12 ~95oC,TniMCLCE-14 ~97oC and TniMCLCE-16 ~98oC), the apparentnematic-isotropic phase transition temperature ofthe dry MCLCE.Jurnal Sains Materi IndonesiaIndonesian Journal of Materials ScienceVol. 12, No. 2,Februari 2011, hal : 134 - 136ISSN : 1411-1098136Figure 3. The dependence of the maximum length change,max, on the concentration of crosslinking, X%, ofMCLCEs in the isotropic is plotted. (a)maximumexpantion, y max and (b). maximum contraction, x max8284868890926 8 10 12 14 16 18y = 75,357 + 0,87143x R= 0,96997x (%)(b)28303234366 8 10 12 14 16 18y = 24,143 + 0,47857x R= 0,98948X(%)(a) MCLCE 16 %. In contrast, MCLCE monotonically shrink(parallel to nˆ ( xˆ) ) is about 82.5 % for MCLCE 8 %, 86 %for MCLCE 12 %, and 86.5 % for MCLCE 14 % and 90 %for MCLCE 16 % (Figure 3(b)).CONCLUSIONThis work has shown that thermo-mechanicaleffects of MCLCE is a function of cross linkerconcentration of MCLCE. The effects showed in thechanges of length. There are maximum expansion andcontraction. Result of the investigation showed that thevalue of maximum contraction is greater and faster thanthe maximum expantion.ACKNOWLEDGMENTWe wish to thank Simon Krause and HeinoFinkelmann for sending us some of the samples used inthese measurements. This work is partially supportedby Hibah Bersaing DIKTI 2009 and Hibah KompetensiDIKTI 2009.REFERENCES[1]. H. KAWAMOTO, Proc. IEEE, 90 (4) (2002)460-500[2]. P. G. DE GENNES, The Physics of Liquid Crystals,Clarendon Press, Oxford, 2nd Edition, (1993)[3]. M. WARNER and E.M. TERENTJEV, LiquidCrystal Elastomers, Clarendon Press, Oxford,(2003)[4]. H. FINKELMANN, H.J. KOCK and G. REHAGE,Macromol. Chem., 2 (1981) 317[5]. Y. YUSUF, Y.ONO, Y. SUMISAKI, P.E. CLADIS,H.R. BRAND, H. FINKELMANN and S. KAI, Phys.Rev. E, 69 (2004) 021710[6]. Y. YUSUF, Y. SUMISAKI and S. KAI, ChemicalPhysics Letters, 382 (2003) 198[7]. Y. YUSUF, Swelling Dynamics andElectromechanical Effects of Liquid CrystalElastomers as An Artificial Muscle, Ph.D. ThesisKyushu University Jepang, (2005)[8]. M. A. ROLANDO, Adsorption and Diffusion inNanoporous Materials, CRC Press Taylor andFrancis Group, NW Suite 300, (2007)processes are shown in this figure. When increasingthe temperature, the planar samples shrink parallel to nˆ( xˆ) and expand perpendicular to nˆ( yˆ). After cooling, allsamples returned to their original shape.Figure 2 shows the relative length changes ofMCLCEs parallel to nˆ(xˆ) and as a function of temperature.Upon increasing temperature, all samples monotonicallyshrank parallel to nˆ( xˆ) with a somewhat faster decreasein the vicinity of Tc (TcMCLCE-8 ~ 84oC, TcMCLCE-12 ~ 95oCTcMCLCE-14 ~97oC and TcMCLCE-16 ~98oC).The relative length changes of planar samples asa function of temperature, λi (T) is defined as the ratio ofexpansion/shrinkage length to the initial length in theisotropic phase (T = 120 oC). Length measurements weremade in the middle of each edge far from the other edges.The relative error was ~± 1 % due to the pixel size of thephoto micrograph.The maximum expansion was in the directionperpendicular to nˆ( yˆ) (Figure 3(a)). The maximumexpansion is about 28 % for MCLCE 8 %, 30 % forMCLCE 12 %, 30.5 % for MCLCE 14 % and 32 % for

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STUDY OF THERMOMECHANICAL EFFECTS OF MAIN CHAIN LIQUID CRYSTAL ELASTOMER AS FUNCTION OF CROSSLINKER CONCENTRATION

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STUDY OF THERMOMECHANICAL EFFECTS OF MAIN CHAIN LIQUID CRYSTAL ELASTOMER AS FUNCTION OF CROSSLINKER CONCENTRATION

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