Flow Properties and Structure of Anisotropic Fluids Studied by Non-Equilibrium Molecular Dynamics, and Flow Properties of other Complex Fluids: Polymeric Liquids, Ferro-Fluids and Magneto-Rheological Fluids

Abstract

In the first part of this Chapter, the anisotropy of the viscosity and shear-induced structural changes of nematic liquid crystals are studied via Non-Equilibrium-Molecular-Dynamics (NEMD) simulations. The pecularities of the viscous behavior of nematics, the description of the anisotropy of the viscosity, and the physical meaning of the various viscosity coefficients associated with the names Ericksen, Leslie, and Miesowicz are presented. Methods for the computation of the viscosity by NEMD simulations of a plane Couette flow are firstly introduced for simple fluids, then the modifications and generalizations needed for the treatment of nematic liquid crystals are discussed. Results are presented for several molecular models. These are perfectly oriented, prolate and oblate, ellipsoidal particles, Gay-Berne particles, and r −12-soft-spheres plus a r −6-interaction with a P 2-anisotropy. The latter two types of model liquid crystals possess both nematic and smetic phases and allow the study of presmectic effects in the nematic phase. Furthermore, data are available for systems with variable degree of order: these are Gay-Berne particles, and partially stiff, partially flexible molecules composed of ten interaction sites. Shear-induced structural changes of the fluids 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 also analysed.