Attractive Interaction between Similarly Charged Colloidal Particles

The pair interactions between the charged colloidal particles dispersed in a solvent are studied theoretically by the integral equation method. The pair potential of the mean forces, accounting for the effective pair interaction between colloidal particles, is calculated from the solution of the Ornstein-Zernike equation with the mean spherical approximation (MSA). An attractive interaction was found between two similarly charged colloidal particles in contrast with the purely repulsive force predicted by the Debye-Huckel theory. Such an attractive interaction provides physical insight for the "condensed" phenomena in charged colloidal dispersions, that is, the coexistence of a "condensed" phase and an "expanded" phase (voids). At the higher concentration and charge on colloidal particles, the effective pair interaction becomes oscillatory.