Precipitate–Coacervate Transformation in Polyelectrolyte–Mixed Micelle Systems

The polycation/anionic-nonionic mixed micelle, poly(diallyldimethylammonium chloride)-sodium dodecyl sulfate/Triton X-100 (PDADMAC-SDS/TX100), is a model polyelectrolyte-colloid system in that the micellar mole fraction of SDS (Y) controls the micelle surface charge density, thus modulating the polyelectrolyte-colloid interaction. The exquisite temperature dependence of this system provides an important additional variable, controlling both liquid–liquid (L–L) and liquid–solid (L–S) phase separation, both of which are driven by the entropy of small ion release. In order to elucidate these transitions, we applied high-precision turbidimetry (±0.1 %), isothermal titration calorimetry, and epifluorescence microscopy which demonstrates preservation of micelle structure under all conditions. The L–S region at large Y including precipitation displays a remarkable linear, inverse Y-dependence of the L–S transition temperature Ts. In sharp contrast, the critical temperature for L–L coacervation Tφ, shows nearly s...