Shear Deformation and Ferroelectricity in Chiral SmC* Main-chain Elastomers

Abstract

Ferroelectric smectic main-chain liquid crystalline elastomers were synthesized and subjected to simple shear deformation to achieve reorientation of the layer structure and the formation of a macroscopic spontaneous polarization. The phase behavior and structural parameters of these elastomers are investigated and discussed. A shear-induced splitting of the X-ray scattering intensity distribution is found. A splitting of the sample in domains of two director orientations that couple differently to the shear deformation is proposed. The smectic layers also move at different affinities depending on their initial orientation. The smectic layer spacing was found to be nearly constant even though the smectic tilt angle changes significantly. The realignment of the smectic layers indicates a migration process, where depending on their original orientation the layer normals are leaving or entering the X-ray scattering plane. The spontaneous polarization was found to be linearly dependent on the dopant concentration with Ps = 30 nC/cm 2 for a system doped with 11 wt % of chiral dopant.

Soft Elasticity in Main Chain Liquid Crystal Elastomers

“…Sánchez-Ferrer et al [64] reported the polydomain to monodomain (P-M) transition caused by uniaxial strain in these materials. The monodomain obtained is termed as pseudo-monodomain [68] because of the conical distribution of the layers around the mechanically induced director. Application of shear deformation perpendicular to the director [61] rendered a perfectly monodomain sample from the pseudo-mono-domain state.…”

Nanoparticle-Liquid Crystalline Elastomer Composites

“…Bent core LCEs have been developed to produce giant flexoelectricity for microscale parasitic power generation [38,39]. Toward this end, main-chain ferroelectric smectic LCEs were synthesized, with analysis of shear deformation and ferroelectricity [40]. However, strong electric fields are necessary to produce actuation in ferroelectric LCEs, and the amplitudes of the resulting mechanical contractions are quite small [35].…”

Negative Poisson's ratio and semisoft elasticity of smectic-Cliquid-crystal elastomers

“…These materials show both the direct piezoelectric effect in pseudo-monodomains [29], as well as the inverse piezoelectric effect [30]. Spontaneous polarization of pseudomonodomains has also been reported [22].…”

“…We will refer to this as a pseudo-monodomain [see Fig. 1(b)] [22] in order to distinguish it from a monodomain, which has both the layer normal and the director uniformly aligned, and a polydomain, which has random director and layer normal alignment. The layer normals in the pseudo-monodomain can be aligned by a second uniaxial deformation perpendicular to one of the layer normals [23], or alternatively by a shear deformation perpendicular to the director [24].…”