Onset of self-assembly in polymer-surfactant systems

(received; accepted) PACS. 61.25Hq – Macromolecular and polymer solutions, polymer melts, swelling. PACS. 61.41+e – Polymers, elastomers, and plastics. PACS. 82.65Dp – Thermodynamics of surfaces and interfaces. Abstract. – The onset of self-assembly in a dilute aqueous solution containing a flexible polymer and surfactant is theoretically studied. Focusing on the effect of the surfactant on polymer conformation and using a conjecture of local instability (partial collapse) of the polymer at the onset of self-assembly, we obtain several simple predictions: (i) polymer–surfactant self-assembly always starts at a lower concentration (cac) than the one required for surfactant–surfactant self-assembly (cmc); (ii) in charged systems the cac increases with salt concentration and is almost independent of polymer charge; (iii) in weakly interacting systems the cac remains roughly proportional to the cmc over a wide range of cmc values. The special case of amphiphilic side-chain polymers strongly supports our basic conjecture. A similarity is found between the partial collapse induced by the surfactant and the effect of impurities on the critical behaviour