(408b) Photorheological Fluids: Micellar Systems with Viscosity Tunable by Light

Fluids having light-tunable rheological properties (i.e., ?photorheological? or PR fluids) may find use in a variety of applications, such as in sensors and microfluidic devices. In our lab, we are investigating PR fluids based on surfactant molecules. We have found that mixtures of the cationic surfactant, cetyl trimethylammonium bromide (CTAB), and the photoresponsive compound, ortho-methoxycinnamic acid (oMCA), self-assemble into long wormlike micelles. Upon irradiation in the UV range, oMCA undergoes a trans to cis photoisomerization, which alters the geometry at the micellar interface. Consequently, the wormlike micelles are transformed into much smaller spherical micelles, and in turn the solution viscosity decreases by more than four orders of magnitude. We will present results from UV-Vis spectroscopy, small-angle neutron scattering (SANS), and rheological studies, that will systematically reveal the light-induced transitions occurring at the molecular, microstructural, and macroscopic scales.