Recent advances in the electric double layer in colloid science

The interaction between charged colloidal particles is mediated by their el ectric double layers. Given that pairs of like-charged particles experience a repulsion, why do some dilute colloidal dispersions become unstable and condense at low ionic strengths? This puzzling paradox appears to have been largely resolved over the past year by a careful analysis of all the contr ibutions to the thermodynamic potential of the dispersion. Condensation can be predicted using the traditional pair repulsion of the Poisson-Boltzmann theory without invoking any long-range attractions in the pair potential. However, it has emerged that one has to go beyond the Poisson-Boltzmann the ory to account for the instability that occurs in confined colloidal disper sions. Other recent advances in the ubiquitous Poisson-Boltzmann theory hav e included effective surface charge approaches in calculating the electroki netic zeta potential, and the modelling of charge regulation in colloidal s ystems. (C) 2001 Elsevier Science Ltd. All rights reserved.