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Photochemical control of micellar solubilization of an oily substance was investigated using the photoisomerization of 4-butylazobenzene-4‘-(oxyethyl)trimethylammonium bromide (AZTMA), a cationic surfactant modified with azobenzene. Examination of the effect of ultraviolet and visible light irradiation on the UV/vis absorption spectrum of aqueous AZTMA solution revealed that the surfactant undergoes reversible isomerization between the trans and cis forms. The critical micelle concentrations (cmc) of the two isomers determined electroconductometrically were 2.7 mM for the trans form and 8.2 mM for the cis form, respectively. Ultraviolet irradiation of aqueous trans-AZTMA solution with solubilized ethylbenzene caused photoisomerization of the trans isomer to release a part of the solubilized ethylbenzene. Subsequent visible light irradiation of the aqueous cis-AZTMA solution produced photoisomerization to the trans isomer to resolubilize the released ethylbenzene. Such control by light of micellar solubilization of an oily substance was found to arise from the differences in both the number and solubilizing capacity of micelles between the two isomers.

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Cobalt(II) meso-tetrakis(4-hexadecylamidophenyl)porphyrin self-assembles in ethanol/1-propanol 2/1 (v/v) to form a rodlike micelle with nanoscale dimensions; the nanorod is a face-to-face aggregate having a hydrophobic corona around a polar core and is thus characterized as a reverse micelle.

We already reported spontaneous vesicle formation in aqueous solutions of bis(11-ferrocenyl(undecyl))dimethylammonium bromide (11-BFDMA), a newly synthesized ferrocene-modified double-chain-type cationic surfactant (Kakizawa, Y.; Sakai, H.; Nishiyama, K.; Abe, M. Langmuir 1996, 12, 921.). We have examined in this study electrochemical control of vesicle formation of 11-BFDMA using the redox reaction of ferrocenyl groups in their molecules. Static light scattering, conductivity, and cyclic voltammogram measurements on the solution revealed that vesicles made of the reduced form of 11-BFDMA disintegrate and change into smaller molecular aggregates including micelles through oxidation of ferrocenyl groups. Oxidation of ferrocenyl groups also caused a remarkable decrease in the solubilization equilibrium constant for benzene in 11-BFDMA solution and release into the bulk phase of benzene solubilized in bimolecular layers of 11-BFDMA vesicles. In addition, glucose entrapped in the inner aqueous phase of the vesicles was found to be released into the bulk phase after about 50% oxidation of 11-BFDMA.