Electric-Field Induced Phase Change in Cholesteric Liquid Crystals

Abstract

Optically-negative cholesteric liquid-crystal films can be transformed to an optically-positive state by applying high d-c electric fields. A phase transformation occurs in which the helicoidal cholesteric structure is converted to either a planar smectic, or a linear nematic, structure. The threshhold field for this transformation has been studied as a function of sample thickness, temperature and composition. Bulk fields are responsible for the phenomenon. It is inferred that the compositional dependences are due to size factors and internal molecular dipole moments.