Responsive release of polyanions from soluble aggregates formed with a hydrolyzable cationic surfactant and a nonionic surfactant

Soluble aggregates formed in dilute aqueous mixtures of polyacrylate (PA), the cationic surfactant decyl betainate (DB), and the nonionic surfactant octaethylene glycol monododecyl ether (C12E8) have been characterized. The aggregates formed can be viewed as mixed micelles of DB and C12E8 with the cationic charge of DB being largely neutralized by PA condensed on the micellar surface. DB contains an ester bond that is susceptible to base-catalyzed hydrolysis under mild alkaline conditions and degradation of DB leads to a decreased attraction of PA to the mixed micelles. It is shown that (1) an increasing extent of DB hydrolysis gives a gradual increase in the fraction of PA released from the mixed aggregates to the surrounding solution, and (2) the rate of hydrolysis, and thus the rate of polymer release, can be controlled by pH. The presented principle can potentially be used in controlled release devices.