Polyelectrolyte-micelle coacervation: Effects of micelle surface charge density, polymer molecular weight, and polymer/surfactant ratio

The effects of micelle charge density, polymer molecular weight, and polyme r-to-surfactant ratio on coacervation were studied by turbidity, dynamic li ght scattering, and electrophoretic mobility in the system composed of the strong cationic polymer poly(diallyldimethylammonium chloride) (PDADMAC) an d oppositely charged mixed micelles of Triton X-100 (TX100) and sodium dode cyl sulfate (SDS). Phase boundaries in the range of SDS mole fraction from 0.30 to 0.50 and in the range of polymer molecular weight from 8.2 x 10(3) to 4.28 x 10(5) were obtained, and coacervate volume ii-action as a functio n of polymer molecular weight was subsequently determined. Three-dimensiona l phase boundaries were used to represent the effects on coacervation of mi celle surface charge density, polymer molecular weight, and PDADMAC-to-SDS ratio. The coacervation region is seen to increase with micelle surface cha nge density and polymer molecular weight (MPT). Both higher and lower polye lectrolyte-to-surfactant ratio can suppress coacervation. An increase in MW reduces the micelle charge required for coacervation and also increases co acervate volume fraction. Coacervation is found to occur when the following conditions are satisfied: the electrophoretic mobility is close to zero, a nd the size of polyelectrolyte-micelle complex is at least about 45 nm.