COMPLEXATION OF AMPHIPHILIC POLYELECTROLYTES WITH SURFACTANTS OF THE SAME CHARGE IN WATER SOLUTIONS

Aqueous solutions containing amphiphilic polycations and micelle-formi ng surfactants of the same charge were examined by potentiometric, flu orescence, sedimentation, and viscometric techniques. Copolymers conta ining N-ethyl-4-vinylpyridinium bromide units and relatively small num bers of either N-dodecyl-4-vinylpyridinium bromide or N-cetyl-4-vinylp yridinium bromide units were used as amphiphilic polycations. The surf actants were dodecyl- and cetyltrimethylammonium bromides and their py ridinium analogs. The formation of copolymer-surfactant complexes in d ilute solution was established, and the complexation behavior was show n to depend upon the copolymer to surfactant concentration ratio in th e mixture. At surfactant concentrations lower than or equal to the cri tical micelle concentration (cmc) complexation leads to compact struct ures via formation of intrachain aggregates containing several hydroph obic chain units and surfactant molecules. At the cmc, the maximum num ber of surfactant ions bound per hydrophobic copolymer chain unit incr eases with increasing length of the polymer side group and decreases f or copolymers that are initially in the compact conformation. At surfa ctant concentrations greater than the cmc the intrachain aggregates ar e disrupted and copolymer coil expansion occurs. The resultant copolym er-surfactant complexes consist of surfactant micelles, each bound to one hydrophobic chain unit of the copolymer.