VISCOSITY COEFFICIENTS NEAR THE NEMATIC-SMECTIC-A PHASE-TRANSITION

The equations of motion of nematic liquid crystals are complemented by the nonlinear Langevin equation for the smectic order parameter fluct uations. The nonlinear terms of this equation describe coupling of the order parameter to velocity and density. An expression for the reacti ve part of the stress tensor is obtained. The complex fluctuation inpu ts into viscosity coefficients are calculated in the frame of the Land au-de Gennes model near the nematic-smectic-A (N-A) phase transition. The sound velocity dispersion and the attenuation dependences on tempe rature, frequency, and the direction of the sound wave propagation are calculated. The results obtained are sensitive to values of two criti cal exponents for correlation lengths.