CRITERION FOR ELECTROSTATIC STABILITY OF DISPERSIONS AT LOW IONIC-STRENGTH

Dispersions in nonaqueous media are often stabilized by electrostatic charge. DLVO theory, which explains charge stabilization in aqueous media quite well, cannot be applied to dispersions at low ionic strength because the Debye length, a necessary parameter for DLVO theory, is usually not known. A theory suitable for dispersions at low ionic strength can be obtained when the repulsion between particles is taken as simple Coulombic repulsion rather than the repulsion due to electrical double layer overlap. With a few approximations an analytical expression for the stability ratio is obtained. The criterion for dispersion stability for many nonaqueous, electrostatically stabilized dispersions can be approximated by the expression PHI-0(2) > 10(3)/Da, where the surface potential is in millivolts, the particle radius is in micrometers, and D is the dielectric constant of the medium.