Thermal Behaviour of the Twist Viscosity in a Series of Homologous Nematic Liquid Crystals

Abstract

We have measured the twist viscosity Y′(T) by the rotating field method, over the entire nematic range of the 4,4′-di-n-alkoxyazoxybenznes (mOAB) from m = 2 to m = 7. The results of these measurements are presented here together with a new development of our previous theory of γ₁(T) which accounts for the free volume variation with temperature and gives the following main result: where S is the order parameter, ϵS is the height of the Maier-Saupe potential, T_O is the temperature of motional “freezing” of the nematic director, and g and ø are nearly constant parameters which may be either computed from other physical data or extracted from the data discussed here. This the oretical result fits very well to the experimental data over the entire nematic range of all the above mentioned materials.