Interaction Parameter

Abstract

Synonyms Energy barrier Definition The interaction energy between particles or drop-lets in a dispersion gives a measure of the repulsion and attraction between them. Three main types of interactions can be identified: elec-trostatic, steric, and van der Waals. The electro-static repulsion G E arises from the presence of electrical double layers surrounding the particles or droplets. The double layers arise from charge separation at the interface which produces a surface charge that is compensated by unequal distribution of counterions (ions with opposite charge to the surface) and co-ions (that have the same charge sign as the surface). The surface charge together with the compensating charge forms the electrical double layer which will have an extension (thickness) that increases with decrease of electrolyte concentration and valency. When two particles or droplets approach to a separation distance h that is smaller than twice the double-layer thickness, repulsion occurs as a result of the overlap of the double layers. Clearly, when the particles or droplets have opposite surface charges, then the interaction between them becomes attractive. The steric repulsion G S arises from the presence of adsorbed nonionic surfactants or polymers. The latter consist of an "anchor" chain that is insoluble in the medium and has a strong affinity to the surface and a "stabilizing" chain that is soluble in the medium and strongly solvated by its molecules. The adsorbed layer is characterized by a thickness d that is determined by the molecular weight of the stabilizing chain and the salvation sheath. When the particles or droplets approach to a distance h that is smaller than 2d, strong repulsion occurs as a result of