ORIENTATIONAL ORDER IN STRAINED NEMATIC NETWORKS

Monodomain nematic networks, formed by cross-linking polymer liquid cr ystals in ordered states, retain a memory of their anisotropic cross-l inking conditions and thereby show novel elasticity and strain-induced nematic transitions. Up to a certain critical strain the nematic dire ctor can experience a barrier to its rotation. Orientational transitio ns can result, and these are investigated using a simple model of nema tic elastomers that allows both the direction and the magnitude of ord er to respond to applied strains. We find two temperature dependent re gimes. At low temperatures where nematic effects are strong, the direc tor rotates the switches with the nematic order largely intact. At hig her temperatures near the thermodynamic phase transition elastic effec ts dominate and applied strain destroys the nematic order before it re -forms in the new direction. This corresponds to the two regimes found experimentally.