Implications of the charge regulation model for the interaction of hydrophilic surfaces in water

Both attraction and repulsion can be found when hydrophilic surfaces in aqueous solutions are only a few nanometers apart. These forces determine to a large extent the interaction of such diverse systems as large molecules, lipid bilayers, and clay platelets. When attraction changes into repulsion below a certain separation, a potential minimum is observed. There is no good explanation for the potential minimum and the repulsion. They are not predicted by the DLVO theory and have therefore been ascribed to a range of phenomena. Here, an existing modification of the DLVO theory by incorporating regulation of the surface charge is used to quantitatively describe published experiments on the repulsion between oxidic surfaces. The agreement suggests that charge regulation is the cause of the minimum and the repulsion. The implications of-the potential minimum are discussed.