Spontaneous, single-walled, equilibrium vesicles can be prepared from aqueous mixtures of simple, commercially available, single-tailed cationic and anionic surfactants. Vesicle size, surface charge, or permeability can be readily adjusted by varying the ratio of anionic to cationic surfactant. Vesicle formation apparently results from the production of anion-cation surfactant pairs that then act as double-tailed zwitterionic surfactants. These vesicles are quite stable in comparison to conventional vesicles prepared by mechanical disruption of insoluble liquid crystalline dispersions.

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ConclusionsExamination of six dyes of increasing amphiphilicity in water-rich microemulsions incorporating oils of different polarity and surfactants with different charge reveals important factors for optimizing dye solubility. In almost all cases, the solubility of dye is much enhanced in microemulsions over that found in pure solvents. It appears that the primary variable is dye amphiphilicity: the more surfactant-like the dye becomes, the greater the solubility in water-rich microemulsions. From the data, it is inferred that the primary site for solubilization of polar dyes is the surfactant-rich interfacial region separating oil and water domains.Acknowledgment. This work was supported by IBM, and we are grateful for the useful comments of Dr. A. H. Sporer.

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