New mechanisms for phase separation in polymer-surfactant mixtures

The cooperative association of ionic surfactants with polymer chains leads to quite navel features in the phase behaviour of polymer solutions. Using an analytic mean-field model, we analyze phase equilibria in solutions of n eutral polymers mixed with ionic surfactants. We predict the possibilities of co-existence between dilute and semi-dilute phases or that between two s emi-dilute phases with different degrees of loading of polymer chains by ad sorbed micelles. The phase separation may be induced either by the variatio n of the concentration of the surfactants. or by increasing the ionic stren gth of the solution or decreasing the solvent strength. Due to coupling of self-assembly of surfactants on the polymer chains and the Theta-transition , the latter is shifted to the range of poor solvent conditions. A critical temperature is identified below which collapse-swelling transition in an i ndividual chain acquires the character of a first-order phase transition.