THE RELATIONSHIP BETWEEN THE MOLAR PARTITION COEFFICIENT AND THE ULTRALOW INTERFACIAL TENSION MINIMUM IN A PETROLEUM SULFONATE/ HYDROCARBON/BRINE SYSTEM

The partitioning of a sodium petroleum sulfonate between heptane and brine yields surfactants with different molar absorptivity and λ_max values in the two phases, except near the point of minimum interfacial tension, e of the surfactant in the heptane phase increases sharply above the point of minimum interfacial tension between the two phases. The molar partition coefficient, M_H/M_W, for the surfactant between the heptane and brine phases is unity at surfactant concentrations in the brine phase below the point of minimum interfacial tension and drops sharply at concentrations above it. The critical micelle concentration of the surfactant in the aqueous phase equilibrated with the heptane phase is considerably below the concentration for minimum interfacial tension