Near-Critical Behavior of the Dynamic Stress-Optical Coefficient in Liquid Crystalline Elastomers

Abstract

Dynamic stress-optical measurements on liquid crystalline elastomers with different cross-linking densities have been carried out in the isotropic phase. The appearance of two relaxation processes in the spectra is probably due to the side-on attachment of the spacers to the mesogenic 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 dependence of the relaxation strengths provides evidence that the cross-linking 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.