H. Oh, A. M. Ketner, R. Heymann, D. Danino, D. Falvey and S. R. Raghavan*
Soft Matter, 9, 5025 (2013)
We describe fluids whose viscosity can be increased million-fold by UV light and back to its original value by visible light. These changes reflect a transition between vesicles and wormlike micelles, caused by photoisomerization of an azobenzene salt. All components of these fluids are commercially available.