Twisting and untwisting of twisted nematic elastomers

A mechanical stretch applied to a monodomain twisted nematic elastomer thin film untwists the helical director distribution into a uniaxially aligned state. If the film thickness is less than the helical pitch, untwisting behavior is stretching direction dependent in the plane normal to the helix axis. We investigate untwisting of twisted nematic elastomers by optical, mechanical, and x-ray scattering methods. We adapt a model for cholesteric elastomers to our observations and find that the material exhibits characteristics with the combined properties of both a smectic and twisted nematic configuration.