Fluctuations in lyotropic and thermotropic liquid crystals near phase transitions.

摘要

We have studied the fluctuations of the five different components of the tensor order parameter for lyotropic and thermotropic liquid crystals near the nematic-isotropic and the uniaxial-biaxial phase transitions. The theoretical calculations have already been done using mean field theory and the Landaude Gennes free energy for both these transitions.; These fluctuations are proportional to the intensity of the light scattered from the sample used. The scattered light is detected by a photomultiplier via an analyzer. The different modes can be selected by orientating the polarization of the incident light and the polarization of the analyzer in different directions.; For the nematic-isotropic transition, a lyotropic sample (25.8% potassium laurate, 7.24% decanol and 66.9% D2O) has been studied as well as a thermotropic sample (5CB). For the uniaxial-biaxial transition, only the lyotropic compound has been studied. Measurements of the scattered light were done by heating or cooling the samples using a computer interfaced temperature controller.