Adhesion versus cohesion in liquid-liquid and solid-liquid dispersions

Abstract

It is found experimentally that, in the absence of specific interactions or electrical effects at the interface, the more stable liquid-in-liquid films are those formed by the liquid of smaller surface tension, which surrounds and separates droplets of the liquid of larger surface tension. A thermodynamic theory postulates that the condition for stability of the film is that the work of adhesion per unit area of interface between the two liquids shall be larger than the specific surface free energy of the liquid of which the film is composed. The deflocculation or flocculation of a dispersed solid in a liquid medium is also shown to depend on the same relation between the work of adhesion and the specific surface free energy of the medium, or, in equivalent terms, on whether the solid particle is “wetted” or not “wetted” by the medium.