Real liquid crystalline elastomers pose really tough problems
Tuesday, May 24, 2005 - 9:30am - 10:05am
Patrick Mather (Case Western Reserve University)
In this talk, I will overview experimental aspects of liquid crystalline elastomer (LCE) materials and thermomechanical behavior. An emphasis will be placed on materials synthesized in our own laboratory. We have separately designed and synthesized rigid nematic networks and compliant smectic-C networks, each existing with polydomain textures at equilibrium and accessible isotropization temperatures. The materials share molecular similarity by use of identical mesogens, but in the nematic case these mesogens are linked directly together by ADMET polymerization, leaving residual unsaturation for crosslinking, while in the smectic-C case the mesogens are bridged by short siloxane spacers that afford the macroscopic compliance. In this presentation I show that despite dramatically different stiffnesses and phase symmetries for these materials, they share in common reversible elongation/contraction on cooling and heating through liquid crystallization/isotropization, respectively. It is argued that this common feature derives from a polydomain-monodomain transition possible in both types of material due to their existence as highly textured materials. I will show further that large strain fixing is possible in both types of materials, such fixing being possible by vitrification of the entire material in the nematic case or of the mesogen-rich layers only in the smectic case. In light of this phenomenology, I will pose broad and specific challenges for the modeling community that are both relevant and necessary for advances in this exciting field.