Cholesteric liquid-crystalline side-on polysiloxanes: Effects of biaxiality on the cholesteric structure

摘要

Biaxial side-on cholesteric copolysiloxanes with laterally attached mesogenic groups were investigated in mixtures with a low molar mass liquid yield crystal. While mixtures with a low concentration of the polymer exhibit the conventional fingerprint texture, for concentrations above about 60 mol-% characteristic irregularities appear in the cholesteric structure that are obviously due to phase biaxiality. Beside the absence of pseudo-isotropic lines, irregular patterns perpendicular to the helix axis emerge and the periodic distance of regions with similar optical properties along the helix axis is strongly disturbed. This suggests that the photonic band gap width of a uniaxial cholesteric phase becomes strongly affected when a phase transformation into a biaxial cholesteric phase occurs.