The Derjaguin–Landau–Verwey–Overbeek (DLVO) theory [1,2] has made it possible to discuss the stability of lyophobic colloids quantitatively. This theory is based on the interaction due to overlapping of electrical double layers and London–van der Waals forces between colloid particles.
Let us consider two immiscible bodies in contact to form an interface. The highly polar body is positively charged, and the other is negatively charged (Koehn’s rule). However, the interface may have the adsorption of ions, dissociation of functional groups, orientation of dipoles, breaking down of chemical bonds, and so on. These affect the real charge densities at the interface, and hence the potential difference at the interface is not explained in terms of such simple dielectric properties of the bodies.
