Effective interactions between charged colloidal particles: Repulsion, attraction and phase separation

The paper summarizes recent theoretical work on the effective interactions between charge-stabilized, spherical colloidal particles. Despite the purel y repulsive nature of the effective pair potential, fluid-fluid phase separ ation is shown to occur at very low salt concentrations, due to a frequentl y forgotten "volume" term. A long-range attractive component to the pair in teraction is predicted when the colloidal particles are confined by charged surfaces (e.g. in slit or pore geometries), in agreement with recent exper imental findings. The importance of excluded volume and solvent effects is briefly discussed.