Phase transitions of nematic rubbers

Single-crystal nematic elastomers undergo a transition from a strongly ordered phase N to an “isotropic” phase I. We show that: a) samples produced under tension by the Finkelmann procedure are intrinsically anisotropic and should show a small (temperature-dependent) birefringence in the high-temperature I phase; b) for the $I\rightarrow N$ transition via cooling there is a spinodal limit but for the $N\rightarrow I$ transition via heating there is no soft mode at the standard spinodal temperature; c) the $N\rightarrow I$ transition is reminiscent of a martensitic transformation: nucleation of the I phase should occur in the form of platelets, making a well-defined angle with the director