A new approach for the characterization of reverse micellar systems by dynamic light scattering

This paper reports the use of dynamic light scattering (DLS) to study reverse micelles formed by the water/Igepal CO-520/cyclohexane system over a large range of global compositions. A novel approach for data analysis is presented, based on the realization that micelles of a given size must be in equilibrium with free surfactant of a fixed concentration. Compilation of the DLS data into sets of fixed micelle size but differing global compositions therefore allows for the determination of parameters such as free surfactant concentration, micellar molar composition, surfactant interfacial area, and aggregation numbers. Importantly, this method gives access to the variation of each of these parameters with micelle size, as is essential for the characterization of reverse micelles formed by nonionic surfactants. This approach constitutes a significant complement to other available characterization methods. The analysis also provides insight into the primary factors controlling the equilibrium distribution of surfactant within the system and the relative stability of the micelles.