CRITICAL-BEHAVIOR OF A CATIONIC-SURFACTANT-WATER-SALT SYSTEM NEAR ANDFAR FROM THE KRAFFT TEMPERATURE

The cationic micellar system docecylammonium chloride + water + KCl ha s been studied by light scattering near the critical point for differe nt concentrations of salt. For the lowest value of salt concentration, the critical point is rather close to the Krafft line, and therefore there is a critical mixture in equilibrium with two noncritical phases : vapor and pure solid surfactant. Both the correlation length and osm otic susceptibility data for the critical mixtures can be accurately d escribed by the usual three-dimensional Ising exponents for all values of the concentration of KCI (C-KCl) This is in agreement with theoret ical predictions that indicate that approaching a critical end point d oes not affect the critical exponents. Two off-critical mixtures have also been studied, and their behavior has been found to be compatible with. the linear model equation of state.