PHASE-SEPARATION AND GEL-LIKE STRUCTURES IN MIXTURES OF COLLOIDS AND SURFACTANT

A colloidal suspension becomes unstable when a sufficient amount of no n-ionic surfactant is added, undergoing a segregation process ascribab le to depletion forces induced by the surfactant micelles. The concent rated phase which separates out is, however, less compact than theoret ically expected and shows stable gel-like features. This anomaly can b e imputed to a dynamic freezing of the segregation process due to the interconnection of transient particle clusters. The results are compar ed with the predictions for the percolation threshold of Baxter adhesi ve hard-sphere model. Small-angle light scattering measurements show t hat the ''gel'' phase is fractally organized over large spatial scales .