Abstract

Liquid crystal elastomers are solids that resist deformation with an elastic modulus appropriate for rubber. However, some special large deformations that induce the liquid-crystal order to rotate though the elastomer can be imposed at almost zero stress. These deformations are said to be soft. Soft elasticity is now well understood in monodomain liquid crystal elastomers (in which the liquid crystal order points in the same direction throughout the sample) but such samples are rather difficult to prepare, especially in anything but a thin film. If a liquid crystal polymer is simply crosslinked to make an elastomer, the results will be a polydomain. We model each domain of a polydomain as a small monodomain and ask whether such polydomains exhibit global soft elasticity. We show that the fabrication history of the sample is critical. Elstomers crosslinked in an isotropic state then cooled to a nematic state whilst a solid have global soft modes while those cooled to a nematic state then crosslinked do not. The addition of smectic phases allows more complicated fabrication histories with a variety of soft and hard behaviour. Finally, I will consider whether any of these polydomains can be used to build actuators.