Statistical theory of the hydrodynamic and relaxation processes in smectic liquid crystals

The methods of nonequilibrium statistical thermodynamics are used to establish a closed system of equations of the relaxation hydrodynamics of smectic liquid crystals of type A. The state of the medium is described by hydrodynamic variables (the particle number density, the momentum and entropy density, and the displacement of the smectic layer) and relaxation variables (the modulus of the complex order parameter and the director). In the region of the smectic-nematic phase transition, the latter exhibit soft-mode behavior. The angular momentum density is used as an additional variable.