Memory effects in liquid crystal elastomers

Abstract

Free-standing monodomain liquid crystal elastomer samples are shown to have a complete memory of the orientational configuration at the time of cross-linking. This memory is demonstrated through samples in which the parent polymer system is first aligned in a magnetic field prior to cross-linking. These films show reversible nematic-isotropic phase transitions and x-ray scattering patterns characteristic of nematic phases. The liquid crystal elastomer films exhibit a remarkable memory effect, in that the sample may be held at temperatures well above the nematic-isotropic transition for extended periods (> 2 weeks), but on cooling into the liquid crystal phase region, both the original director alignment and the degree of preferred orientation are recovered. It is demonstrated that these novel memory effects are equilibrium in nature. The origins of this phenomena in terms of coupling between the mesogenic side-chains and the polymer network are discussed

Nanoparticle-Liquid Crystalline Elastomer Composites

“…The resulting LCEs exhibit an isotropic-nematic transition temperature around 80-90 °C. An alternative side-chain nematic LCE can be formed from mesogens containing acrylate groups [58][59][60]. The acrylate groups can be polymerized under UV light in the presence of a suitable photo-initiator, or can undergo radical polymerization.…”

Stacking nematic elastomers for artificial muscle applications

“…an artificial muscle, was first suggested decades ago by de Gennes [8]. In particular, uniqueness of nematic LCEs stems from the fact that they exhibit reversible macroscopic and anisotropic contraction as the material is heated and cooled through the nematic to isotropic phase transition temperature, T NI [9]. The macroscopic uniaxial contraction occurs parallel to the nematic director and arises from ordered mesogenic units that are anisotropically incorporated into a polymerized and cross-linked network.…”

Nematic Elastomers Cross-Linked by Rigid Rod Linkers

“…8 One explanation for semisoftness has been advanced. If chains fluctuate in composition, for instance if they are random copolymers 9,10 or if there are variations in structure due to incomplete reactions, then each chain may have a different shape since each will be made up of differing combinations of nematic elements. Therefore the deformation that is soft for a mean chain will cause rotations of distributions that are not quite right for any particular given chain.…”