Structure and elastic properties of smectic liquid crystalline elastomer films

Stannarius, Ralf; Köhler, Rosemarie; Dietrich, U.; Lösche, Mathias; Tolksdorf, C.; Zentel, Rudolf

doi:10.1103/physreve.65.041707

Cited by 42 publications

(45 citation statements)

References 37 publications

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“…IV. However, it is consistent with the work of Stannarius et al, who performed mechanical experiments on Sm-A LCE balloons and found Mooney-Rivlin coefficients in the range 0 < c MR < 0.1 [11].…”

Section: Model Parameterssupporting

confidence: 92%

Numerical study of stretched smectic-Aelastomer sheets

Brown

Adams

2013

Phys. Rev. E

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We present a numerical study of stretching monodomain smectic-A elastomer sheets, computed using the finite element method. When stretched parallel to their smectic layer normal the smectic layers are unstable to a transition to a buckled state. We model macroscopic deformations by replacing the microscopic energy with a coarse grained effective free energy that accounts for the fine-scale layer buckling. We augment this model with a term to describe the energy of deforming buckled layers, which is necessary to reproduce the experimentally observed Poisson ratios postbuckling. We examine the spatial distribution of the microstructure phases for various stretching angles relative to the layer normal and for different length-to-width aspect ratios. When stretching parallel to the layer normal the majority of the sample forms a bidirectionally buckled microstructure, except at the clamps where a unidirectionally buckled microstructure is predicted. When stretching at small inclinations to the layer normal the phase of the sample is sensitive to the aspect ratio of the sample, with the bidirectionally buckled phase persistent to large angles only for small aspect ratios. We relate these theoretical results to experiments on smectic-A elastomers.

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Section: Model Parameterssupporting

confidence: 92%

Numerical study of stretched smectic-Aelastomer sheets

Brown

Adams

2013

Phys. Rev. E

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“…[6] Similar observations could be expected from homeotropically oriented thin elastomer films, produced by photo-crosslinking of a surface aligned S A polymer. However, neither spontaneous shape changes at the smectic-isotropic phase transformation nor a significant impact of the oriented layer structure on the rubber elastic modulus were observed for these materials, [12][13][14][15][16][17] which is in clear contrast to the S A LSCEs presented in this study. For elastomer E1 with the lowest crosslinking density the layer compression modulus B ¼ 1.1 Â 10 7 N Á m À2 is significantly larger than those observed for conventional low molar mass liquid crystals, where B is typically in the order of 1-5 Â 10 6 N Á m À2 for low measuring frequencies.…”

Section: Discussioncontrasting

confidence: 92%

“…[11][12][13][14] While for all S A LSCEs aligned by uniaxial stretching highly anisotropic mechanical properties and a macroscopic shape change at the LC-isotropic phase transformation have been reported, [4,5,8] no pronounced anisotropy of the elastic moduli and the macroscopic chain conformation was observed for homeotropic thin film elastomers. [12][13][14][15][16] This behaviour was attributed to the existence of microphase separated polysiloxane sublayers, which are characteristic for diluted polysiloxanes and might reduce the smectic layer compression modulus significantly. [17] In this paper we present the first experimental results on bulk S A LSCEs with homeotropic orientation, prepared by the anisotropic deswelling technique.…”

Section: Introductionmentioning

confidence: 99%

Mechanics of Homeotropically Ordered Smectic‐A Elastomers with Global Oblate Chain Conformation

Kramer

Finkelmann

2011

Macromol. Rapid Commun.

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Smectic-A elastomers combine one-dimensional translational order of rod-like segments with the rubber elasticity of a polymer network. In recent years, detailed investigations were carried out on elastomers showing a global prolate chain conformation. In this communication, the first experiments on fluorinated SA elastomers exhibiting a global oblate chain conformation are presented, where the polymer chains are on average compressed along the layer normal of the lamellar phase structure. The mechanical anisotropy is studied by means of thermoelastic experiments and stress-strain measurements. For the first time, the layer compression modulus B of smectic elastomers is directly measured. B is significantly larger as compared to conventional low molar mass liquid crystals and decreases significantly with increasing local disorder introduced by the isotropic crosslinker.

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“…While the first deformation process causes layer reorientation above a characteristic threshold stress, the second process leaves the structure unmodified and indicates the in-plane fluidity of the smectic layers [4][5]. SmC elastomers, significant because of their optical and ferroelectric properties such as in the case of chiral molecules (SmC Ã phase) [6], have also been synthesized.…”

Section: Introductionmentioning

confidence: 99%

Mechanical Deformations in Smectic-C Main-Chain Liquid-Crystalline Elastomers

Sánchez-Ferrer¹,

Finkelmann²

2009

Molecular Crystals and Liquid Crystals

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A novel crosslinked smectic-C Main-Chain Liquid-Crystalline Elastomer (MCLCE) has been synthesized by polycondensation of vinyloxy-terminated mesogens, tetramethyldisiloxane and pentamethylpentaoxapentasilecane. The introduction of the functional vinyloxy group allows the synthesis of well-defined networks having low soluble content and good mechanical properties. Networks having a macroscopic uniformly ordered director and a conical distribution of the smectic layer normal with respect to the director are mechanically deformed by uniaxial and shear deformations. Under uniaxial deformations two processes were observed: parallel to the director the mechanical field directly couples to the smectic tilt angle while perpendicular to the director a reorientation process takes place. A shear deformation parallel and perpendicular to the director causes a uniform layer orientation and the network exhibits a smectic-C monodomain phase having a macroscopic uniform director and layer orientation. This process is reversible for shear deformation perpendicular and irreversible by applying the shear force parallel to the director.

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Structure and elastic properties of smectic liquid crystalline elastomer films

Cited by 42 publications

References 37 publications

Numerical study of stretched smectic-Aelastomer sheets

Numerical study of stretched smectic-Aelastomer sheets

Mechanics of Homeotropically Ordered Smectic‐A Elastomers with Global Oblate Chain Conformation

Mechanical Deformations in Smectic-C Main-Chain Liquid-Crystalline Elastomers

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