Complexation of Amphiphilic Polyelectrolytes with Surfactants of the Same Charge in Water Solutions

Abstract

Aqueous solutions containing amphiphilic polycations and micelle-forming surfactants of the same charge were examined by potentiometric, fluorescence, sedimentation, and viscometric techniques. Copolymers containing N-ethyl-4-vinylpyridinium bromide units and relatively small numbers of either N-dodecyl-4-vinylpyridinium bromide or N-cetyl-4-vinylpyridinium bromide units were used as amphiphilic polycations. The surfactants were dodecyl- and cetyltrimethylammonium bromides and their pyridinium analogs. The formation of copolymer-surfactant complexes in dilute solution was established, and the complexation behavior was shown to depend upon the copolymer to surfactant concentration ratio in the mixture. At surfactant concentrations lower than or equal to the critical micelle concentration (cmc) complexation leads to compact structures via formation of intrachain aggregates containing several hydrophobic chain units and surfactant molecules. At the cmc, the maximum number of surfactant ions bound per hydrophobic copolymer chain unit increases with increasing length of the polymer side group and decreases for copolymers that are initially in the compact conformation. At surfactant concentrations greater than the cmc the intrachain aggregates are disrupted and copolymer coil expansion occurs. The resultant copolymer-surfactant complexes consist of surfactant micelles, each bound to one hydrophobic chain unit of the copolymer.