ELASTIC INSTABILITY AND STRIPE DOMAINS IN LIQUID-CRYSTALLINE ELASTOMERS

We consider the elastic and orientational response of a uniform nemati c elastomer subjected to an extension perpendicular to its director. B y allowing a possibility of local shear in the material, we show that the effect of ''soft elasticity'' leads to a new regime of director re orientation, through a highly non-uniform stripe domain state (in cont rast to earlier predictions and observations of a discontinuous unifor m director jump). The molecular theory developed here gives prediction s on two levels: of the general texture of the stripe state plus the i nterval of strains in which it occurs, and of topological properties o f the director rotation that are very general and depend only on chain anisotropy of elastomer but not on details of the specific material. On the other hand, parameters like the threshold strain for the domain formation depend on the chemical composition and on the model used to describe its effect. We discuss and explain experimental observations of stripe domains both in the perpendicular geometry and when the str etching direction is at an oblique angle to the director, leading to a symmetric stripes and different topology.