CRITICAL PHENOMENA AT THE TRANSITION FROM THE ISOTROPIC TO NEMATIC AND CHOLESTERIC PHASES IN LIQUID CRYSTALS

Phenomena occurring at the transition from the isotropic to nematic and cholesteric phases in liquid crystals are investigated. It is verified that the susceptibility exponent (gamma) = 1 for both materials with positive or negative dielectric anisotropies. A search for the nematic-isotropic critical point was conducted with materials of high anisotropy. The dielectric strength of the materials together with turbulent effects at the transition prevented reaching the critical point.;The transition between the helical cholesteric phase and the disordered isotropic phase sometimes occurs through one or more intermediate phases. These are the blue phases. The structures of the blue phases are investigated in the homologous series of cholesteryl-n-alkanoates by examining Bragg reflections. We observe structures which are consistent with b.c.c. (or s.c.), f.c.c., and non-cubic lattices. In addition to finding transitions between differing structures within the blue phase region for four homologs, we report a new type of structural change in cholesteryl propionate in which the intensity of one Bragg reflection decays as another grows as a function of temperature.