The Extended DLVO Theory

In the classical Derjaguin, Landau, Verwey and Overbeek (DLVO) theory electrical double layer repulsions represented one half of the interactions studied and these repulsions closely resembled those occurring in aqueous systems. However, when using water as the liquid medium it is indispensable to extend the classical DLVO theory by including the polar interaction energies which always occur in water, using the Lewis acid–base approach. (Using the classical DLVO approach for an aqueous system limits one to content oneself with analyzing only about 10% of the forces that are actually operating in aqueous systems.) Each one of the three different non-covalent forces involved in the extended DLVO (XDLVO) theory, i.e.: (1) Lifshitz–van der Waals (LW), or electrodynamic interactions; (2) Lewis acid-base (AB) or electron-acceptor/electron-donor interactions and: (3) electrical double layer (EL) interactions, decays according to fundamentally different regimens. This requires that for each one of the three types of interaction the free energies as a function of distance be determined and treated separately. It is only after each energy versus distance curve thus obtained for LW, AB and EL interactions has been obtained separately, that all three (expressed in the same energy units) may be added together, to obtain the final XDLVO plot.