Effect of anionic surfactant structure on critical concentrations and compositions of sodium alkylbenzene sulfonate/polyoxyethylene octylphenol/tetradecyltrimethylammonium bromide mixed micelles

Abstract

The model for multicomponent nonideal mixed micelles used via the regular solution approximation allows accounting for the critical micelle (CMC) of binary or ternary mixtures obtained with nΦCm (anionic surfactant), TTAB (cationic surfactant), and OP(EO)₈ (nonionic surfactant). The anionic/cationic interaction is much higher than the ionic/nonionic interactions; this is probably due to the high electrostatic attraction between molecules which have opposite charges. We have found that anionic/cationic interaction appears to depend very slightly on the anionic surfactant structure, while anionic/nonionic interaction increases with the length of the alkyl chain of the anionic surfactant, but does not depend significantly on the position of the polar and head branching. — The introduction in the model of the pair interaction parameters, determined from the CMC of the binary mixtures, gives valuable predictions for the CMC and for the micelle compositions of the ternary mixtures. CMC of the ternary mixture are lower than the CMC of each component of the mixture. Contrary to that which is expected for an ideal mixing, the mixed micelles are principally composed of ionic surfactant molecules. Our results seem to show that these behaviors could depend slightly on the position of the polar head branching and on the length of the alkyl chain of the anionic surfactant.