Prediction of Critical Micelle Concentrations and Synergism of Binary Surfactant Mixtures Containing Zwitterionic Surfactants

Abstract

We present a simplified “working model” of a recently developed molecular-thermodynamic theory of mixed surfactant solutions which can be utilized to predict critical micelle concentrations (cmc's) and synergism of binary surfactant mixtures in which one of the surfactants is zwitterionic. Given (i) the chemical structures of the hydrophilic heads and the hydrophobic tails of the surfactants, (ii) the cmc's of the pure surfactants, and (iii) the solution conditions such as temperature and the concentration of added salt, the model can predict the βAB interaction parameter characterizing synergism in mixed micelle formation and the mixture cmc as a function of solution composition. The model considers electrostatic interactions as the main contribution to synergism in mixed micelle formation, initially accounting for these interactions at an approximate level. The model applies only to surfactants with linear hydrocarbon tails and neglects synergism due to steric interactions between the surfactant heads o...