ABSTRACT
The dispersion stability, expressed as the constancy of the number of particles per unit volume, indicates resistance to sedimentation and coagulation. In unstable dispersions the concentration of particles in the upper dispersion layers decreases because of sedimentation and or flocculation. The nature of the dispersion medium is one of the main factors controlling dispersion stability. The dispersion medium affects the solid-liquid interfacial tension and stabilization of the dispersion by influencing the adsorption of the dispersant and configuration of the adsorbed dispersant. Electrostatic stabilization is based on an ionic repulsion between approaching particles that prevents attachment by a Coulombic energy barrier. Electrostatic interactions are important even in dispersions stabilized by an adsorbed polymer, because the charge density of particle surfaces affects the configuration of the adsorbed polymer layer. The effectiveness of a polymeric dispersant depends on the solvency of the dispersion medium. The electrophoretic mobility has been measured to calculate the zeta potential and the adsorbed layer thickness.
