EFFECT OF SURFACE ALIGNMENT LAYERS ON THE CONFIGURATIONAL TRANSITIONSIN CHOLESTERIC LIQUID-CRYSTALS

To understand the mechanism behind the pitch change during the transie nt planar to the planar state transition of a cholesteric liquid cryst al (while it is relaxing from the homeotropic state to the planar stat e), we studied a more controlled situation of pitch change in a thermo chromic liquid crystal. We studied the pitch change in the liquid crys tal, as a function of temperature, under various surface alignment con ditions such as homogeneous and homeotropic surface alignments. In a c ell with homogeneous surface treatment, the liquid crystal showed a di scontinuous pitch change, while the pitch change was rather continuous in a cell with homeotropic treatment. The numerical simulations also showed an existence of continuous pitch change in a homeotropic cell, but not in a homogeneous one. This led to a prediction that when a cho lesteric material is switched from the homeotropic state to the planar state, the transition may be much faster for the homeotropically trea ted cell as compared to the homogeneously treated cell. We performed e xperiments to verify this prediction with a chiral nematic mixture. In deed, the homeotropic to planar state transition time of a homeotropic cell was 5 msec, much faster compared to about 200 msec for correspon ding transition in a homogeneous cell.