Dispersion Stability of Fine Particles in Nonaqueous Solvent

The effects of surface polarity of particles and the properties of solvent and dispersant (nonionic surfactant) on the dispersion stability of alumina, zeolite and surface-treated silica particles were examined in nonaqueous solvents. The degree of stability was evaluated by a coagulation rate method, which was newly proposed in addition to the sedimentation and rheological methods. As a result, it was found that the solubility parameter of solvent required to provide the maximum stability decreased with increasing surface polarity of particles. This tendency was explained in terms of the van der Waals' interaction between particles, assuming that the electrostatic interaction was neglected in a nonpolar solvent. Maximum stability was achieved at the maximum adsorbed amount of dispersant, as estimated by the adsorption model of dispersant on a particle surface.