Onset of self-assembly in polymer-surfactant systems

School of Physics and Astronomy Raymond and Beverly Sackler Faculty of Exact Sciences Tel Aviv University, 69978 Tel Aviv, Israel

Received: 8 March 1999
Accepted: 23 August 1999

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 partial collapse of the polymer at the onset of self-assembly, we obtain results which agree with known experimental observations: 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 general results concerning the effect of impurities on critical phenomena.