UNIAXIAL-TO-BIAXIAL CHOLESTERIC AND NEMATIC PHASE-TRANSITIONS ON A LYOTROPIC ALCOHOL-FREE MIXTURE

Interferometric measurements of the chirality-induced biaxiality in the vicinity of the uniaxial-to-biaxial cholesteric transition of the lyotropic system potassium laurate, decylammonium chloride, H2O, and brucine sulfate are reported. The mean-field approach to describe the cholesteric-to-cholesteric transition allows an estimate of the ratio between coefficients of the Landau expansion. The values of the bare correlation length, xi0 approximately 1000 angstrom, calculated are larger than in lyotropic systems with alcohol. The chirality-induced biaxiality measurements in the limit of zero elastic field (q2=0) and the birefringence measurements in the nematic phase confirm critical properties of the uniaxial-to-biaxial nematic transition. The critical exponents for the order parameter (beta) and the susceptibility (gamma) are in good agreement with the values calculated for the XY model.