A correlation for three-phase behavior of cationic surfactant-oil-water systems

The phase behavior of cationic surfactant/oil/water/alcohol systems was systematically scanned to correlate the attainment of three-phase microemulsion-oil-water systems with the following formulation variables: water phase salinity as sodium chloride concentration, oil alkane carbon number (ACN) or equivalent ACN when the oil phase is not an alkane, surfactant alkyl chain length, surfactant hydrophilic group (both amine salts at acid pH and quaternary ammonium compounds at neutral pH), alcohol and temperature effects. The numerical correlation is mathematically similar to the one found for anionic surfactant systems. Differences in coefficient and parameter values allow comparisons between both types of ionic surfactant systems. The linear expression corroborates the theoretical interpretation proposed in other publications.