Europhys. Lett, 48 (2), pp. 170-176 (1999)
Onset of self-assembly in polymer-surfactant systems
H. Diamant and D. Andelman
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 in final form 23 August 1999)
PACS. 61.25Hq - Macromolecular and polymer solutions; polymer melts;
PACS. 61.41 - Polymers, elastomers, and plastics.
PACS. 82.65Dp - Thermodynamics of surfaces and interfaces.
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.
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