COHERENT TRANSLATION AND LIBRATION AS SEEN BY A SHEAR VISCOSITY OF A CLASSICAL HARD-SPHERE FLUID

Thermodynamic transport properties, such as a shear viscosity, can pro vide evidence of coherent phenomena. In a dilute gas, the coherence ta kes the form of free translation interrupted by collisions and this ef fect is reflected in the wavevector dependence of the shear viscosity. In a dense fluid, near the solidification transition or in a glass, t he viscosity begins to diverge as a consequence of highly correlated r ecollisions. In this work, a generalized Langevin formulation of the k inetic theory of hard spheres is used to calculate the shear viscosity in these two limiting regimes. In the collision dominant (i.e., cagin g) regime, the divergence of the shear viscosity can be compensated by the vanishing self diffusion coefficient. The D eta product is well b ehaved, illustrates aspects of Stokes-Einstein behavior, in rough acco rd with the hydrodynamic predictions (obtained using slip boundary con ditions) and suggests a Stokes-Einstein breakdown in accord with exper iments on glassy ortho-terphenyl liquids. (C) 1995 American Institute of Physics.