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.