Order fluctuation dynamics of nematic liquid crystal in a binary system: MBBA/biphenyl

The twist mode of a nematic liquid crystal, composed of a nematogenic solvent (MBBA) and a nonnematogenic solute (biphenyl), is investigated by the spectral composition of quasielastically scattered light from uniformly oriented samples in the forward depolarized configuration. The twist diffusivity coefficient K22/γ1 as a function of temperature and composition is found to be separable into two factors, one involving solely the equilibrium nematic order and the other attributed to an additional composition-dependent term. With use of the twist viscosity data in the literature, the twist elastic constant K22 of pure MBBA over the entire nematic region is deduced, and is shown to remain finite at the nematic–isotropic transition.