Critical micelle concentrations of nonionic surfactants in organic solvents: Approximate prediction with UNIFAC

The objective of this study was to model the critical micelle concentration (cmc) of nonionic surfactants in nonaqueous systems using the UNIFAC group contribution method. For the prediction of the cmc the phase separation ap proach was used, where the micellar phase is approximated as a second liqui d phase resulting from the liquid-liquid equilibrium between the solvent an d the surfactant, with the necessary activity coefficients predicted by UNI FAC. The limited amount of literature data for reverse micelle formation in nonaqueous systems was used to test the predictions, varying surfactant ty pe, solvent, and temperature. The most promising model was the modified UNI FAC of B, L. Larsen, P. Rasmussen, and A. Fredenslund (Ind. Eng. Chem. Res. 26, 2274 (1987)). Since most nonionic surfactants contain oxyethylene chai ns, a new set of parameters was evaluated for this group, leading to satisf actory predictions. The average deviation between the predicted and the exp erimental cmc's was about 0.1 log units. (C) 2001 Academic Press.