Long-range interactions in model colloidal dispersions with surface charge distributions

Abstract

The theoretical model, which is based on the density functional approach, has been developed for studying the electrostatic properties of colloidal dispersions (modified colloidal primitive model; MCPM) containing hard-spherical ions with a homogeneous surface charge distribution. The mean-spherical approximation for the multi-component charged ions has been used to account for the electrostatic ion correlation effects. The present study reflects the importance of the charge distribution of macroion in determining the ionic structure and mean forces acting on the macroions. Compared with the MCPM, the colloidal primitive model (CPM), on which the colloidal charge is assumed to be in the center of particle, shows very long-range electrostatic properties and mean force acting on the macroions because of the strong cross correlation between the hard-sphere contribution and the Coulomb interaction. The long-range attractions and repulsions in the charged colloidal dispersions originate from the entropic effects and are found at high packing fractions of the colloidal ions.