Spherical colloids: effect of discrete macroion charge distribution and counterion valence

We report the coupled effects of macroion charge discretization and counterion valence in the primitive model for spherical colloids. Instead of considering a uniformly charged surface, as it is traditionally done, we consider a more realistic situation where discrete monovalent microscopic charges are randomly distributed over the sphere. Monovalent or multivalent counterions ensure global electroneutrality. We use molecular dynamics simulations to study these effects at the ground state and for finite temperature. The ground state analysis concerns the counterion structure and charge inversion. Results are discussed in terms of simple analytical models. For finite temperature, strong and weak Coulomb couplings are treated. In this situation of finite temperature, we considered and discussed the phenomena of ionic pairing (pinning) and unpairing (unpinning). (C) 2002 Elsevier Science B.V. All rights reserved.