Photoinduced formation of threadlike micelles from mixtures of a cationic surfactant and a stilbene amphiphile

This study examined the influence of ultraviolet (UV) irradiation on aqueous surfactant solutions containing an anionic stilbene derivative (sodium [4-[(E)-2-(4-butylphenyl)ethenyl]phenoxy]acetate; C4StilNa) as a photoresponsive skeleton. Prior to UV irradiation, an aqueous solution of cetyltrimethylammonium bromide (CTAB) and C4StilNa was a low-viscosity fluid forming spheroidal micelles. Exposure of the low-viscosity fluid to UV light resulted in the formation of threadlike micelles and an increase in the viscosity of the aqueous CTAB/C4StilNa solution. ¹H nuclear magnetic resonance spectroscopy indicated that the photochemically induced isomerization and dimerization reactions of C4StilNa molecules had occurred in the aggregates due to UV irradiation. Overall, the structural transformation of the stilbene groups in the C4StilNa molecules with the photochemical reactions leads to an increase in the critical packing parameter and consequently a photoinduced transition of spheroidal micelles to threadlike micelles.