Aggregation behavior of surfactants in polymer gel networks

Aggregation behavior of anionic sodium dodecyl sulfate and a nonionic surfa ctant, polyoxyethylene (p = 10) nonylphenyl ether, in the inside and outsid e of polymer hydrogels has been studied through solubilization techniques o f an oil-soluble dye, measurements of surfactant concentration in the aqueo us phase of the gel interior, and binding isotherms of the surfactants onto polymer chains of the gel. The surfactant aggregation is strongly affected by the presence of polymer gel networks. Interestingly, it is found that t he nonionic surfactant cannot form micelles inside the gel at concentration s greater than even the critical micelle concentration in the outer bulk so lution. The anionic surfactant molecules adsorb onto the polymer chains of a relatively hydrophobic N-isopropylacrylamide gel but not onto the hydroph ilic acrylamide (AAm) gel. In the AAm gel, the anionic surfactant forms mic elles in the aqueous solution phase inside the gel, avoiding the exclusive space of the polymer chains.