Orientational Order in Strained Nematic Networks

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