PREDICTION OF CRITICAL MICELLE CONCENTRATIONS OF NONIDEAL BINARY SURFACTANT MIXTURES

We have simplified a recently developed molecular-thermodynamic theory of mixed surfactant solutions to obtain a "working model" which can be utilized to predict critical micelle concentrations (cmc's) of nonideal binary surfactant mixtures where at least one of the surfactant species is ionic. The required inputs of the model are (i) the cmc's of the pure surfactants, (ii) the overall surfactant composition and other solution conditions such as temperature and salt type and concentration, and (iii) the chemical structures of the hydrophobic and hydrophilic moieties of both surfactant species. We find that the model yields reasonable quantitative predictions for anionic-nonionic and cationic-nonionic surfactant mixtures of single-tailed surfactants having linear hydrocarbon chains or linear phenyl hydrocarbon chains. We view the simplified "working model" for the prediction of mixture cmc's as a valuable preliminary screening tool in the design and selection of nonideal surfactant mixtures of practical importance.