Aerosol-OT surfactant forms stable reverse micelles in aploar solvent in the absence of water

Normal micelle aggregates of amphiphilic surfactant in aqueous solvent are formed by a process of entropically driven self-assembly. The self-assembly of reverse micelles from amphiphilic surfactant in non-polar solvent in the presence of water is considered to be an enthalpically driven process. While the formation of normal and reverse surfactant micelles has been well characterized in theory and experiment, the nature of dry micelle formation, from amphiphilic surfactant in non-polar solvent in the absence of water, is poorly understood. In this study, a theory of dry reverse micelle formation is developed. Variation in free energy during micelle assembly is derived for the specific case of AOT surfactant in isooctane solvent using atomistic molecular dynamics simulation analyzed using the energy representation method. The existence and thermodynamic stability of dry reverse micelles of limited size are confirmed. The abrupt occurence of monodisperse aggregates is a clear signature a critical micelle concentration, commonly observed in the formation of normal surfactant micelles. The morphology of large dry micelles provides insight into the nature of the thermodynamic driving forces stabilizing the formation of the surfactant aggregates. Overall, this study provides detailed insight into the structure and stability of dry reverse micelles assembly in non-polar solvent.