Ion size correlations and charge reversal in real colloids

For many decades, the Gouy-Chapman model, whose cornerstone is the Poisson-Boltzmann equation, has been the traditional approach to describing the electric double layer (EDL). Since the early 1980s, a great amount of theoretical work (mostly computer simulations and integral equation theories) has proved that this classical picture of the EDL presents severe failures in the case of electrolytes with multivalent ions, as a result of neglecting ionsize correlations. The overlooking of the phenomenon of charge reversal is probably one of the most representative examples of such deficiencies. This work is a critical survey on the relevance of ion size correlations in real colloidal systems (focused mainly on solutions with multivalent counterions). A sophisticated electrophoresis theory (in which ionic steric correlations are taken into account) will be applied to analyze experimental data, which will be also compared with predictions of the classical approach. In addition, we will discuss to what extent ion size correlations contribute to charge reversal in colloids of biological nature and other real colloids. Unlike the classical Poisson-Boltzmann approach, the presented theory describes the charge inversion that occurs within aqueous latexes when increasing the trivalent aqueous electrolyte concentration well above the mmolar range. (c) 2005 Elsevier B.V. All rights reserved.