BROWNIAN DYNAMICS AND KINETIC GLASS-TRANSITION IN COLLOIDAL SUSPENSIONS

Structural slowing down in a simple model of a polydisperse suspension of charge-stabilized colloidal particles is explored by molecular-dynamics and Brownian-dynamics simulations. The former ignore solvent effects, but allow a comparison with recent experimental, numerical, and theoretical work on "fragile" glass formers. Solvent friction is taken care of in the irreversible Brownian-dynamics simulations, but solvent-induced hydrodynamic interactions between colloidal particles are neglected. Self-diffusion is found to proceed by hopping process, near and below the kinetic glass transition temperature, even in the case of Brownian dynamics, where cooperative phonon processes are overdamped. Newtonian and Brownian dynamics lead to qualitatively different relaxations of the density fluctuations. The density autocorrelation functions calculated with Brownian equations of motion show no evidence of beta relaxation. The simulation results are discussed in the light of recent dynamic-light-scattering experiments on concentrated colloidal suspensions.