Study of a Cholesteric Liquid Crystal Polymer in Solution in a Low Molar Weight Liquid Crystal: Phase Diagram and Electric Field Effect

Abstract

Abstract We have studied the effect of an electric field on a binary mixture between a cholesteric liquid crystal polymer and a low molar weight liquid crystal from results a cholesteric polymer film in a confined geometry. The phase diagram shows, moreover an excellent compatibility between the compounds, a very large variation of the cholesteric pitch. According to the magnitude and the frequency of the applied electric field, various behaviours are observed: stable homeotropic nematic, stable birefringent filaments, “fingerprint” texture, …. We have focused our study on the effect of an electric field on the filament texture corresponding to a large cholesteric pitch. The transition of a texture with filaments to a homeotropic structure is described by the existence of two optical thresholds (the appearance of the homeotropic and the disappearance of the filaments) whom the variation is studied according to the frequency. We are describing particular phenomena added to this general behaviour, like the nucleation and the growth under field of quasi perfect spirals issue of the bending of the filaments just before the obtaining of the homeotropic state. Besides, we give an example where the quenching of the spiral texture is possible thanks to the polymeric compound of the binary mixture. From the configuration of the filament proposed by Lequeux or Oswald et al., it is possible to imagine a mechanism where, in given conditions, a propagation of the authors' structure is produced.