Repulsive Van Der Waals Interactions: Their Role in Various Separation Methods

Abstract

It has long been surmised, as a theoretical curiosity, that conditions could arise under which the sign of the van der Waals interaction between two different uncharged bodies, surrounded by a liquid, might be negative, i.e. that such bodies would repel each other. This possibility is implicit in Hamaker's classical paper on van der Waals-London interactions, although, remarkably enough, Hamaker somehow became persuaded that this view was erroneous, and wrote his paper with the apparent purpose to gainsay it: “If two particles are embedded in a fluid and the London-van der Walls force between particles and fluid is greater than between the particles themselves, it might be thought that the resultant action will be a repulsion rather than an attraction. As has been pointed out to the author by Dr. J.H. de Boer, this conclusion does not hold. Owing to a peculiar property of the London-van der Waals forces, the resultant force is generally attractive even when the particles are surrounded by fluid. This is a matter of considerable interest which warrants a detailed discussion.”¹ However, In a more recent review on Hamaker constants, Visser stated explicitly: “When two materials are immersed in a liquid medium, and the interactions of each of these materials with that of the liquid medium is larger than the interaction between these materials themselves, spontaneous separation can occur due to dispersion forces only.”² Fowkes demonstrated such a repulsive interaction with poly (tetrafluoroethylene)-glycol-iron oxide.³