Molecular interactions and the quantitative prediction of synergism in mixtures of surfactants

Abstract

The equations for determining the nature and strength of the interaction between two different surfactants in mixed monolayers at various interfaces (β ^σ value) or in mixed micelles (β ^m value), based upon nonideal or regular solution theory, and their utilization for quantitative prediction of synergism, are reviewed. From the data on numerous systems, where both the chemical structures of the two surfactants and their molecular environments were changed, it appears that electrostatic forces between the two hydrophilic groups dominate the interaction. The replacement of air by a liquid aliphatic hydrocarbon or by a nonpolar hydrophobic solid (Parafilm, Teflon) reduces the (attractive) interaction between the two surfactants slightly, but leaves unchanged other chemical structural effects.

The quantitative relationships between the β ^σ and β ^m values and the existence of synergism in surface or interfacial tension reduction efficiency, synergism in mixed micelle formation, and synergism in surface or interfacial reduction effectiveness are given, along with relationships for the mole fraction of the two surfactants at the point of maximum synergism and for the value of the relevant property at that point. Experimental and calculated values are compared. Future advances in the field may be in non-detergency industrial applications.