Restabilization of Electrosterically Stabilized Colloids in High Salt Media
V S. Stenkamp, P M. McGuiggan, J C. Berg
For electrostatically stabilized colloids, an increase in salt concentration typically causes a decrease in stability, until the electrical double layer is collapsed, in which case the instability remains as salt concentration is increased further. In cases when adsorbed polymer is used to impart stability, the onset of aggregation can most often be correlated with the onset of poor polymer solvency. Therefore, it is anticipated that when a charged latex is stabilized by a thin nonionic polymer which is salted out, the colloidal stability should either decrease or remain constant upon an increase in salt concentration. In the present work, however, an increase in stability is observed for several salts at relatively high concentrations, a phenomenon referred to herein as restabilization. The specific circumstances in which this unexpected behavior occurs and the possible causes for it are discussed.