Variation of the Network Anisotropy of Cholesteric Side Chain Elastomers

Abstract

A series of cholesteric side chain elastomers with odd and even numbers of atoms along the spacer chain was prepared. Varying the content of odd and even spacer groups resulted in anisotropic main chain conformations changing from prolate to oblate. The conformation anisotropy was characterized by temperature dependent measurements of the sample dimensions. The transmission spectra for polarized light of the elastomer films were recorded under uniaxial mechanical stress, applied perpendicular to the helical axis of the cholesteric liquid crystal. With increasing strain a blue shift of the selective reflection due to a contraction of the helix along its axis was observed. In the case of a non-vanishing conformation anisotropy in addition a distortion of the regular helical structure was indicated by changes in the transmission spectra for linearly polarized light. This distortion was found to be much weaker than predicted by theory.