Surface forces and colloidal behaviour

Abstract

The landmark DLVO theory of colloid stability sought to explain the stability of lyophobic colloids in terms of the interplay between attractive dispersion forces, and repulsive electrical (Coulombic) forces between particle surfaces. The net interaction energy between two particles (resulting from these so-called surface forces) as a function of surface separation can exhibit a maximum, a deep (primary) minimum and/or a shallow (secondary) minimum, giving stable, unstable or weakly flocculated dispersions. Other surface forces include steric forces arising from grafted or adsorbed polymer chains on the surfaces. Unadsorbed polymer can result in attractive depletion forces between particles, and polymer molecules that bridge particles can cause flocculation. Other forces mentioned are oscillatory structural forces, attractive hydrophobic forces and repulsive hydration forces between surfaces in water. Direct measurement of surface forces between both solid/liquid interfaces and between liquid/liquid interfaces is discussed at the end of the chapter.