“Soft elasticity” — deformation without resistance in liquid crystal elastomers

Warner, Mark; Bladon, Peter; Terentjev, E. M.

doi:10.1051/jp2:1994116

Cited by 200 publications

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“…We propose simple sinusoidal functions for the director rotation and the displacement field [Eqs. (2)], with i denoting the displacement along the i axis. These functions vary sinusoidally in the x direction with wave vector k, and the wave vector q has the value d so that the director and displacement fields satisfy both the homogeneous boundary condition and the no-slip boundary condition at the substrates (z d 2 ).…”

Section: Prl 96 147802 (2006) P H Y S I C a L R E V I E W L E T T E mentioning

confidence: 99%

“…(1) gives the free energy density of an incompressible gel subject to the periodic deformation and director rotation described by Eqs. (2). We Taylor expand this function in around 0 and keep only terms of O 2 or greater.…”

Section: Prl 96 147802 (2006) P H Y S I C a L R E V I E W L E T T E mentioning

confidence: 99%

“…The coupling of these two effects in liquid-crystalline elastomers and gels gives rise to unique phenomena such as soft elasticity in which certain director rotations and network strains cost no free energy in the ideal case. Soft elastic modes are predicted and well understood theoretically by a molecular theory of nematic rubber elasticity [1][2][3]. However, a significant limitation in testing existing theories is the difficulty in preparing well-characterized networks.…”

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Buckling Instability in Liquid Crystalline Physical Gels

et al. 2006

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In a nematic gel we observe a low-energy buckling deformation arising from soft and semisoft elastic modes. We prepare the self-assembled gel by dissolving a coil -side-group liquid-crystalline polymercoil copolymer in a nematic liquid crystal. The gel has long network strands and a precisely tailored structure, making it ideal for studying nematic rubber elasticity. Under polarized optical microscopy we observe a striped texture that forms when gels uniformly aligned at 35 C are cooled to room temperature. We model the instability using the molecular theory of nematic rubber elasticity, and the theory correctly captures the change in pitch length with sample thickness and polymer concentration. This buckling instability is a clear example of a low-energy deformation that arises in materials where polymer network strains are coupled to the director orientation. DOI: 10.1103/PhysRevLett.96.147802 PACS numbers: 61.30.ÿv, 61.41.+e, 82.70.Gg Liquid-crystalline elastomers and gels combine the orientational order of liquid crystals and the translational order of a polymer network. The coupling of these two effects in liquid-crystalline elastomers and gels gives rise to unique phenomena such as soft elasticity in which certain director rotations and network strains cost no free energy in the ideal case. Soft elastic modes are predicted and well understood theoretically by a molecular theory of nematic rubber elasticity [1][2][3]. However, a significant limitation in testing existing theories is the difficulty in preparing well-characterized networks. Many approaches have been undertaken to prepare liquid crystal elastomers, including free-radical polymerization of bulk liquid crystal acrylates and diacrylates [4], free-radical polymerization of diacrylates in the presence of liquid crystals [5,6], and side-coupling reactions with poly(methylsiloxane) [7]. Unfortunately, these approaches result in nematic elastomers and gels with heterogeneities in the polymer network and, in the case of many gels, phase separation of the polymer network from the liquid crystal host [8,9]. More recently, self-assembly of block copolymers has been used as an approach to create model liquid crystal networks [10 -12]. We have utilized self-assembly of a triblock copolymer that has a narrow molar mass distribution and a very long midblock to produce well-defined nematic gels [10,11]. This gel facilitates comparison to present theories which assume the material is lightly cross-linked and single phase.In this Letter, we present a study of the effects of nematic rubber elasticity in thin layers of uniformly aligned gels contained between rigid parallel plates. Using polarized optical microscopy, we observe a banded texture that arises in response to small temperature changes. We propose that this texture represents a buckling deformation made possible by the presence of soft and semisoft elastic modes. We formulate a description based on the molecular theory of nematic elastomers that incorporates soft and semisoft elasticity as well as l...

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Section: Prl 96 147802 (2006) P H Y S I C a L R E V I E W L E T T E mentioning

confidence: 99%

Section: Prl 96 147802 (2006) P H Y S I C a L R E V I E W L E T T E mentioning

confidence: 99%

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Buckling Instability in Liquid Crystalline Physical Gels

et al. 2006

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“…This idealized theory predicts a class of zero-energy deformations (Olmsted 1994;Warner et al 1994)-any deformation of the form…”

Section: Nematic Elastomersmentioning

confidence: 99%

Strain-induced polarization in non-ideal chiral nematic elastomers

Biggins

2009

Proc. R. Soc. A.

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Symmetry arguments are advanced that, although ideal chiral nematic elastomers cannot show strain-induced electrical polarization, non-ideal ones can. Phenomenological arguments are then presented, which predict a simple and universal form for the direction and strain dependence of the polarization. A microscopic minimal model is also developed, which predicts the same form. Finally, an example of a polarization-strain curve is calculated for a typical experimental geometry. In this geometry, the polarization is exactly zero at both small and large strains, but pronounced for a large set of intermediate strains corresponding to the strains that cause incremental rotation of the nematic director.

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“…One of the striking aspects of the neo-classical theory is that it predicts soft elasticity, i.e., deformations involving large strains but costing zero energy 20 . As support for soft deformations and the neo-classical model, Verwey, Warner & Terentjev 21 interpreted the observed formation of stripes as a consequence of soft elasticity, which has been further investigated by DeSimone & Dolzmann 22 and Conti et al 23,24 .…”

Section: Introductionmentioning

confidence: 99%

Orientational order and finite strain in nematic elastomers

Fried

Sellers

2005

The Journal of Chemical Physics

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Nematic elastomers exhibit large, spontaneous shape changes at the transition from the hightemperature isotropic phase to the low-temperature nematic phase. These finite deformations are studied here in the context of a nonlinear, properly invariant, variational theory that couples the orientational order and elastic deformation. The theory is based on the minimization of a freeenergy functional that consists of two contributions: a nematic one due to the interaction of the mesogenic units and an elastic one arising from the stretching of the cross-linked polymer chains. Suitable choices for these two contributions allow for large, reversible, spontaneous shape changes in which the elastic deformation can affect the isotropic-nematic transition temperature. The change in transition temperature as well as the magnitude of the resulting spontaneous deformation are illustrated for various parameter values. The theory includes soft elasticity as a special case but is not restricted to it.

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“Soft elasticity” — deformation without resistance in liquid crystal elastomers

Cited by 200 publications

References 0 publications

Buckling Instability in Liquid Crystalline Physical Gels

Buckling Instability in Liquid Crystalline Physical Gels

Strain-induced polarization in non-ideal chiral nematic elastomers

Orientational order and finite strain in nematic elastomers

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