Mechanism of relaxation from electric field induced homeotropic to planar texture in cholesteric liquid crystals

We have investigated the relaxation process from a homeotropic structure to the planar one in a cholesteric liquid crystal. The relaxation occurs afte r switching off the electric field. We have developed a new experimental ph otography technique with a time resolution of about 20 mu s and applied it to the investigation of textural changes during the transition. After the l iquid crystal goes through a defect-free transient planar structure, the de velopment of the cholesteric helices occurs in two stages. Direct observati ons have shown that formation of the final equilibrium state involves a nuc leation process. We used optical retroreflection spectroscopy and measureme nt of light scattering to observe changes of the cholesteric pitch and orie ntation of helices as well as the size of domains in time for various treat ments of the glass substrates. We have also proposed a theoretical model th at describes the experimental data satisfactorily.