Synergism in binary mixtures of surfactants: VIII. Effect of the hydrocarbon in hydrocarbon/water systems

The surfactant mixture C 12H 25SO 3 −Na +-C 12H 25N +(CH 2C 6H 5)CH 2COO − (C 12BMG) was investigated at various hydrocarbon/water interfaces. The hydrocarbons used were hexadecane, dodecane, heptane, cyclohexane, heptamethylnonane, isooctane, and toluene. Using nonideal solution theory, the molecular interaction parameters for mixed monolayer and mixed micelle formation, β LL σ and β LL M , respectively, and parameters determining synergism in interfacial tension reduction efficiency, mixed micelle formation, and interfacial tension reduction effectiveness were calculated. It was found that, for this surfactant mixture, the replacement of air by a hydrocarbon as the second phase against water reduced molecular interaction in the mixed monolayer or mixed micelle and reduced synergism in interfacial tension reduction efficiency, mixed micelle formation, and interfacial tension reduction effectiveness.