Rotational Viscosities of Nematic Sodium Decylsulfate, 1-Decanol, D₂O Mixtures

Abstract

The studied mixtures of sodium decylsulfate, 1-decanol and D₂O show a sequence of three nematic phases, a low temperature uniaxial phase N_L, a biaxial phase N_bx, and a higher temperature uniaxial phase N_c. We report rotation experiments in magnetic fields to determine the anisotropy of the diamagnetic susceptibility and the rotational viscosity, electrical conductivity measurements to study mi-cellar order and realignment in magnetic fields, and birefringence measurements and relaxation studies on thin surface aligned films. The measured rotational viscosities in N_C range from a few poise to nearly 100 poise. There is a strong pretransitional decrease of the viscosity with decreasing temperature at the N_C-N_bx transition. The data in the N_L range indicate also a pretransitional decrease as the N_L-N_bx transition is approached. Near the transition the viscosity is considerably smaller in the lower temperature N_L - phase than in N_C. The conduction anisotropy and birefringence in N_C show some differences in the temperature dependence. Both decrease slightly as the uniaxial-biaxial transition is approached but the decrease of conduction anisotropy is more pronounced.