COLLOIDAL PHASE-TRANSITIONS IN AQUEOUS NONIONIC SURFACTANT SOLUTIONS

Highly negatively charged polystyrene particles suspended in aqueous n onionic surfactant solutions undergo a phase transition when the solut ion is in close proximity to the cloud curve of the binary nonionic su rfactant-water mixture. This transition is present only on the surfact ant-rich side of the critical point of the binary mixture and is chara cterized by the presence of brilliant colors in the solution. These co lors indicate the formation of polycrystalline aggregates of the polys tyrene particles. This particle phase behavior is similar to the aggre gation behavior observed for particles dispersed in aqueous solutions of 2,6-lutidine and its analogs. The observed behavior is best interpr eted in terms of the appropriate ternary phase behavior and results fr om immiscibility between the particles and one of the liquid component s. Although the details and origins of this unfavorable interaction va ry from system to system, the same general pattern of phase behavior i s observed in many mixed colloidal systems.