KINETIC HETEROGENEITIES AND NONLINEAR RHEOLOGY OF HIGHLY SUPERCOOLED LIQUIDS

Supercooled liquids with soft-core potentials are studied via molecula r dynamics simulations in two and three dimensions in quiescent and sh eared conditions. We demonstrate that bond breakage events among parti cle pairs occur collectively in clusters. The average life time, tau(b )((gamma) over dot ), of bonds tends to the alpha relaxation time, tau (alpha), for weak shear, (gamma) over dot << 1/tau(alpha), and decreas es as 1/(gamma) over dot for strong shear, (gamma) over dot >> 1/tau(a lpha). The structure factor, S-b(q), of the broken bonds may be fitted to the Ornstein-Zernike form. The correlation length, xi, is uniquely expressed in terms of tau(b)((gamma) over dot) as xi similar to tau(b )(gamma) over dot(1/4) in two dimensions and xi similar to tau(b)((gam ma) over dot)(1/2) in three dimensions for any T and (gamma) over dot in glassy states. The viscosity is of order tau(b)(gamma) over dot for any (gamma) over dot, so the shear stress tends to a limiting stress for (gamma) over dot tau(alpha), >> 1. (C) 1998 Elsevier Science B.V. All rights reserved.