VISCOSITY OF ISOTROPIC HARD PARTICLE FLUIDS

A kinetic theory for the frequency-dependent shear viscosity eta(omega ) of isotropic fluids, composed of non-spherical hard convex bodies, i s extended in two ways. First, the theory is reformulated to allow eta (omega) to be expressed directly in terms of matrix elements involving the shear stress tensor rather than in terms of the transverse moment um correlation function. Second, relaxation of the antisymmetric compo nent of the stress, 'due to coupling with spin angular momentum, is ex plicitly incorporated; this corrects an error in a previous version of the theory. The revised kinetic theory:is compared with computer simu lations for hard ellipsoids of revolution of axial ratio 2, 3, 5 and 1 0. Both the symmetric and antisymmetric contributions to eta(omega) ar e well reproduced. Coupling with the collective molecular second-rank orientation tensor remains an important factor in determining the vari ation of eta(omega) from high to low frequencies; the prediction of th e magnitude of the associated dip in eta(omega) is significantly impro ved. The new version of the theory is also more successful in predicti ng values of the zero-frequency shear viscosity eta, the shear-orienta tion coupling parameter R, and the Stokes-Einstein (-Debye) products D -s eta and D-r eta. (C) 1996 American Institute of Physics.