Rotational Viscosity Measurement of a Binary Mixture Showing Both Induced Smectic and Re-Entrant Nematic Phases

The rotational viscosity has been measured in a binary system of two polar nematic compounds, exhibiting nematic – smectic Ad – re-entrant nematic phase sequence. In both the nematic and re-entrant nematic phases, the rotational viscosity values are about 0.5 Pa s and show small temperature dependence. However, in the smectic Ad phase, the rotational viscosity values initially increase with decrease in temperature to attain a maximum near the middle of the smectic phase and then decreases with further decrease in temperature. The activation energies associated with rotational viscosity for the nematic phase are distinctly higher than those obtained for the re-entrant nematic phase.