When Ion-Ion Correlations are Important in Charged Colloidal Systems

Abstract

Colloidal particles, biopolymers and membranes all carry charges in an aqueous environment. The molecular source of these charges can be cova-lently bound ionic groups like phosphates, sulfates, carboxylates, quarte-nary ammoniums or protonated amines. The carboxylates and amines can titrate in response to pH changes, while the other groups remain charged except at extreme conditions. A particle, a self assembled aggregate or a polymer can also acquire a charge by adsorption of a small charged molecule like an amphiphile. The interactions between charged mesoscopic objects is strongly influenced by the net charge and the electrostatic interactions provide one of the basic organizing principles in both colloidal sols and in living cells. These electrostatic interactions can be both attractive, leading to association, and repulsive resulting in dispersion.