Applications of net repulsive van der Waals forces between different particles, macromolecules, or biological cells in liquids

Abstract

When the sum of the interactions of two different materials with a liquid medium is larger than the sum of the interactions between the two materials and those between the molecules of the liquid medium themselves, the net van der Waals interaction between the two materials, immersed in that liquid medium, will be repulsive. It can be demonstrated that this situation prevals when the surface tension of the liquid medium has a value intermediate between the values of the interfacial tensions of the two materials. Net repulsive van der Waals interactions are shown to be responsible for the rejection of particles by solidifying melts, and for the incompatibility of polymers in solution. Repulsive van der Waals forces can be employed in the dissociation of antigen—antibody complexes, in the elution steps of hydrophobic chromatography, affinity chromatography and reversed-phase chromatography, and generally in the detachment of liquid and solid materials from solid substrates (e.g., washing, dry-cleaning, petroleum extraction from oil shales or tar sands). Finally, the implications of extremely small van der Waals attractions are discussed in connection with the stability of particle suspensions, and the strategy for devising optimal destabilization procedures.