Photo-induced transformation of wormlike micelles to spherical micelles in aqueous solution

A photo-responsive system composed of an imidazolium-type surfactant 1-hexadecyl-3-methylimidazolium bromide ([C16mim]Br) and a commonly photosensitive aromatic compound trans-cinnamic acid (trans-CA) was studied through UV spectra, 1H NMR, and rheological measurements. In aqueous solution, the compounds [C16mim]Br and trans-CA can self-assemble to form viscoelastic wormlike micelles. Through UV irradiation, the CA molecules exhibit molecular photoisomerization from trans- to cis-, which results in a change of the molecular critical packing. The wormlike micelles transform into spherical micelles after UV irradiation, which is also confirmed by rheological measurements.