Mixed solvent critical micelle concentration

A spiropyran compound bearing a pyridinium group and a long alkyl chain behaves as a surfactant. The components shown in Scheme 1 exhibit reverse photochromism in polar solvents. The colored merocyanine form is more stable than the spiropyran form in the dark. Upon photoirradiation at A>510 nm, the polar merocyanine form is converted to the hydrophobic spiropyran form so that the CMC (critical micelle concentration) of the surfactant decreases. Consequently, when the initial concentration is set between the CMC of the two forms, photoirradiation induces a sudden formation of micelles at a certain conversion to the spiropyran form corresponding to the CMC of the mixed micelle of the two forms. 

Variation of the Critical Micelle Concentration and Apparent Charge of the Micelles in the Mixed Solvents... 

There is some disagreement within the surfactant literature as to the exact definition of solubilization, particularly as the ratio of surfactant to additive decreases, and one approaches the nebulous frontier between swollen micellar systems and the micro- and macroemulsion regions. For present purposes, solubilization will be defined as the preparation of a thermodynamically stable, isotropic solution of a substance (the additive ) normally insoluble or only slightly soluble in a given solvent by the addition of one or more amphiphilic compounds at or above their critical micelle concentration. By the use of such a definition, a broad area can be covered that includes both dilute and concentrated surfactant solutions, aqueous and nonaqueous solvents, all classes of surfactants and additives, and the effects of complex interactions such as mixed micelle formation and hydrotropes. It does not, however, limit the phenomenon to any single mechanism of action. 

Photochemical processes in heterogeneous systems, and across micelle boundaries in particular, clearly has great potential. The photolysis of amphipathic alkylcobaloximes in mixed micelles shows a co-operative effect owing to structure.The photoreduction of anthraquinone in aqueous micellar solution has been compared with that in non-aqueous solution.The dimerization of 3-(n-butyl)cyclopentenone is solvent-dependent and the ratio of isomeric products depends on surfactant concentration. It is suggested that this can be used as a means of critical micellar concentration determination. 

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