Viscous behavior and shear-induced structural changes in perfectly oriented liquid crystals

The anisotropy of the viscosity and shear-induced structural changes are studied via nonequilibrium molecular dynamics (NEMD) simulations for two types of model liquid crystals which possess both isotropic and smectic phases. These models are (a) perfectly oriented Gay-Berne particles and (b) r(-12)-soft-spheres plus an r(-6)-interaction with a P-2-anisotropy. Results are presented for the Miesowicz viscosity coefficients in the nematic phase. Presmectic effects are observed. Structural changes are revealed by snapshots of configurations and by the static structure factor, presented in analogy to scattering experiments. The shear-induced transition from the smectic to the nematic phase is analyzed. Similarities between magnetorheological fluids and discotic systems which can form columnar phases are discussed.