Sharp steepness of molecular reorientation for nematics containing liquid crystalline polymer

The reorientational steepness of nematic liquid crystalline molecules is strongly dependent on the elastic constants of the liquid crystalline director. The steepness increases with decreasing the ratio of elastic constants of the bend mode to the splay one, K3/K1 when the homogeneous or twisted alignment of nematics is transformed to the homeotropic one. It has been suggested that the elastic constants are affected by the geometrical shape of a liquid crystalline molecule and a short-range ordering for the alignment of liquid crystalline molecules. The composite systems films being composed of side-chain type liquid crystalline polymer (PS6EC) and low molecular weight nematic liquid crystal (E7) were prepared by a solvent cast method. The phase transition behaviors and the aggregation state of the composite system were investigated on the basis of the DSC, polarizing optical microscopy and x-ray diffraction studies. The magnitude of K3/K1 and the reorientational steepness were evaluated by an electric capacitance measurement of the homogeneous cell. It became apparent from x-ray diffraction studies that the smectic-like short-range ordering among mesogenic molecules increases with increasing the fraction of PS6EC even in a nematic state of the composite system. The magnitude of K3/K1 was anomalously small, nearly zero, in an intermediate region between the smectic and the nematic phases for the (PS6EC/E7) composite system. At that region, furthermore, a discontinuous jump in the reorientation of liquid crystalline molecules, i.e., sharp steepness in an electro-optical switching, was successfully achieved.