On the theory of irreversible processes in molecular liquids and liquid crystals, nonequilibrium phenomena associated with the second and fourth rank alignment tensors

A theory for nonequilibrium phenomena primarily associated with the molecular orientation in liquids and liquid crystals is developed within the framework of irreversible thermodynamics. The alignment tensors of rank 2 and 4 are taken into consideration as additional macroscopic variables. With appropriate assumptions concerning the dependence of the internal energy, specific volume and the entropy on the alignment, a dynamic Landau theory is obtained. Nonlinear relaxation equations are derived for the alignment tensors. They possess zero and nonzero stable stationary solutions corresponding to the isotropic and nematic phases of a liquid crystal when the temperature is above or below the transition temperature. Some further applications of the relaxation equations are discussed, in particular fluctuations of the intensity of the depolarized component of scattered light.