Prof. Amy Shen
University of Washington, Seattle, U.S.
Local: Centro de Tecnologia, Bloco G, sala 205
Shear-induced structures (SIS) are known to form in flows of wormlike micellar solutions. In simple shear cases these structures (SIS) are temporary and disintegrate upon cessation of the flow; while in certain mixed-flow cases these flow-induced structured phases (FISPs) are stable and long-lived. Here, we compare the flow of a micellar solution in a microfluidic device containing an array of microposts, with that of Poiseuille flow in a microchannel. In the former case a stable permanent FISP can be produced, whereas in the latter no structured phase (SIS or FISP) occurs. Using the fluorescent dye Nile Red, we are able to observe the local micelle concentration of the solutions during flow. We find that in the microfluidic device containing microposts, we can generate local concentration variation on the order of up to 25% that strongly correlates with the FISP, while in the microchannel with Poiseuille flow, no measurable concentrations differences are observed. The relevance of these concentration variations for the formation of the FISP are discussed. The use of Nile Red as a probe into the local micelle concentration may also serve as a simple and complementary optical tool (i.e. with birefrigence and light scattering) towards investigation of a variety of flow-induced structures, as opposed to more complicated and expensive scattering techniques that involve neutrons and x-rays.
Amy Shen received her Ph.D in Theoretical and Applied Mechanics from University of Illinois at Urbana-Champaign in October 2000. She was a postdoctoral fellow at Harvard University from 2000-2002. Amy Shen is an associate professor in Mechanical Engineering and Chemical Engineering at University of Washington and served as the director of soft matter and microfluidics laboratory. Amy’s research is focused on the complex fluids and the hydrodynamics of these materials to create morphologies and structures that can find application in the nanotechnology, biotechnology, microelectronics, and energy related materials. Amy received Ralph E. Powe Junior Faculty Enhancement Award in 2003 and the National Science Foundation's CAREER Award in 2007. Amy is also an honor member of Phi Kappa Phi and Pi Tau Sigma.