NEAR-CRITICAL BEHAVIOR OF THE DYNAMIC STRESS-OPTICAL COEFFICIENT IN LIQUID-CRYSTALLINE ELASTOMERS

Dynamic stress-optical measurements on liquid crystalline elastomers w ith different cross-linking densities have been carried out in the iso tropic phase. The appearance of two relaxation processes in the spectr a is probably due to the side-on attachment of the spacers to the meso genic groups. The relaxation frequencies and the relaxation strengths of the processes show critical behavior in qualitative agreement with the Landau-de Gennes theory. The strong cross-linking density dependen ce of the relaxation strengths provides evidence that the cross-linkin g points locally perturb the liquid crystalline order. A comparison of the dynamic mechanical and the dynamic stress-optical behavior of the samples indicates that the stress-optical processes are triggered by fast contributions to the mechanical spectrum.