PHASE-BEHAVIOR OF POLYMER-SURFACTANT SYSTEMS IN RELATION TO POLYMER-POLYMER AND SURFACTANT-SURFACTANT MIXTURES

Novel phase diagrams of systems of water and two cosolutes of colloida l size, either macromolecules or surfactant micelles, are presented. F or a mixture of two oppositely charged surfactants, a complex phase di agram is obtained with several liquid crystalline phases and equilibri um vesicles. There is a strong tendency for two surfactants to mix and form a range of structures governed by geometrical packing and electr ostatic interactions. In recent years, surfactant self-assembly in the presence of different polymers has attracted a great interest, both f rom fundamental and applied aspects. Attractive or repulsive interacti ons are observed depending on the system. For the former case, dilute solutions may be analysed in terms of a binding of the surfactant to t he polymer or a depression of the critical micelle concentration of th e surfactant by the polymer. An important feature of these solutions i s thus that the surfactant molecules, also when interacting intimately with a polymer, give micellar-type structures. The phase behavior of polymer-surfactant systems has only recently attracted greater attenti on but has been shown most significant for the understanding of the in teractions involved. Different types of phase separation phenomena are encountered including segregative and associative types. For systems of a polyelectrolyte and an oppositely charged surfactant, an associat ive interaction is observed leading to phase separation into one solut ion concentrated in both polymer and surfactant and one very dilute so lution. In the presence of an electrolyte, phase separation may be eli minated and, at higher concentrations, a polymer incompatibility type of phase separation may result. It is found fruitful to analyse the ph ase diagrams of polymer-surfactant systems with those of polymer-polym er and surfactant-surfactant mixtures as a basis. Analogies and differ ences are discussed and it is found that polymer-surfactant systems sh ow basic similarities to polymer-polymer systems, while surfactant mix tures are different, which is due to the exchange of surfactant molecu les between micelles and the formation of mixed micelles and other agg regates. Surfactant mixtures are, therefore, not displaying a segregat ive type of phase separation.