INTERACTIONS IN DODECYLAMMONIUM CHLORIDE DODECYL-SULFATE SYSTEMS

Phase boundaries for mixtures of dodecylammonium chloride (DDACl) and sodium dodecyl sulfate (NaDS) are determined over a wide range of concentrations. The phase behavior strongly depends on the molar ratio and concentration of surfactant present. In the range of concentrations where monomer-micelle equilibrium prevailed the mixed micelles of different composition are formed. The addition of oppositely charged surfactant enhance the apparent degree of counterion dissociation (alpha). Results reveal the existence of asymmetry on NaDS-rich systems; more pronounced shift of CMC(NaDS) with DDACl addition, higher increase of alpha(Na) values and the two regions of mixed micelles formation. The deviation of precipitate-solubility boundary from linearity is explained by phase transitions from precipitate and coacervate to mixed micelles. The concentrations at which coacervate is formed are lower than it would be found in the absence of DDADS.