Self-assembly in mixtures of polymers and small associating molecules

The interaction between a flexible polymer in a good solvent and smaller as sociating solute molecules such as amphiphiles (surfactants) is considered theoretically. Attractive correlations, induced in the polymer because of t he interaction, compete with intrachain repulsion and eventually drive a jo int self-assembly of the two species, accompanied by partial collapse of th e chain. Results of the analysis are found to be in good agreement with exp eriments on the onset of self-assembly in diverse polymer-surfactant system s. The threshold concentration for self-assembly in the mixed system (criti cal aggregation concentration, cac) is always lower than the one in the pol ymer-free solution (critical micelle concentration, cmc). Several self-asse mbly regimes are distinguished, depending on the effective interaction betw een the two species. For strong interaction, corresponding experimentally t o oppositely charged species, the cac is much lower than the cmc. It increa ses with ionic strength and depends only weakly on polymer charge. For weak interaction, the cac is lower but comparable to the cmc, and the two are r oughly proportional over a wide range of cmc values. Association of small m olecules with amphiphilic polymers exhibiting intrachain aggregation (polys oaps) is gradual, having no sharp onset.