GRAND CANONICAL BROWNIAN DYNAMICS SIMULATION OF COLLOIDAL ADSORPTION

摘要

A dynamic simulation of colloidal adsorption has been developed to probe the effects of colloidal interactions on the kinetics and extent of adsorption. The simulation accounts for diffusion by Brownian dynamics to a homogeneous planar adsorption surface from a region of constant chemical potential. A grand canonical Monte Carlo routine is used periodically to re-equilibrate this region. Particle motion in the plane of the surface is subject to either unrestricted diffusion or zero diffusion. Deryaguin-Landau-Verwey-Overbeek pair potentials are used to characterize both particle-particle and particle-surface interactions. The pair potential parameters were chosen to mimic (separately) polystyrene latex microspheres and small globular proteins, two classes of charged colloidal particles for which experimental adsorption data exist. The simulation qualitatively captures the variation in adsorptive capacity with ionic strength distinct to each system: fractional coverage increases for polystyrene latex adsorption but decreases for protein adsorption with increasing salt concentration. In the former, strong lateral repulsion between adsorbed particles appears to govern the extent of adsorption, whereas in the latter, the extent of adsorption is more strongly affected by the screening of the weak attraction between the particle and the surface. Excellent quantitative predictions for polystyrene latex adsorption with and without surface diffusion are obtained without adjustable parameters. (C) 1997 American Institute of Physics. [References: 47]