Reverse Micelle Formation of C12-S-C12n-Heptane and Their Solubilization for Water

The critical reverse micelle concentrations of quaternary ammonium Gemini surfactants C12-s-C12·2Br (s=2, 3, 4, 5, 6, 8, 12) in n-heptane (cmcw) have been determined by the water solubilization method. These values are smaller than the critical micelle concentration (cmcaq) in aqueous solution, where C12-s-C12 2Br forms normal micelles. The cmcw as a function of s goes through a maximum at s=4, which is similar to the variation regularity of cmcaq with s. The saturated amount of water solubilizing in the reverse micelles measured by both the water solubilization method and the conductivity method show a maximum at about s=5. This is attributed to the change in folded conformation of the spacer chain.