Nonequilibrium Phase Transition and Pattern Formation in Nematic Liquid Crystal

We study the phase transition between nematic liquid crystals and isotropic phases during continuous cooling and heating. The transition temperature T-c was examined using ac-driven electroconvection (EC). A phase diagram including various EC patterns in the voltage-temperature plane was established. Moreover, the voltage V-dependent T-c shift was determined at a fixed frequency f. The frequency f-dependent T-c was measured at fixed values of V below and above the onset of EC. Results showed that T-c is highly sensitive to the structures of EC patterns with various director fields and flows depending on V and f.