(332b) Flow Transitions in Miscible Fluids of High Viscosity Contrast in a Microfluidic Expansion

Authors: 
Dylla-Spears, R., University of California at Berkeley
Muller, S. J., University of California at Berkeley
dela Cruz, J., University of California at Berkeley
Yuan, K., University of California at Berkeley
Lee, J. S., LG Chem Research Park


We have experimentally investigated the behavior of miscible, Newtonian fluids of differing viscosities as they encounter a microfluidic expansion. A low molecular weight polyethylene glycol solution of known viscosity (η1) is hydrodynamically focused into a narrow jet using a lower viscosity polyethylene glycol solution (η21). The fluid streams enter an expansion, where a series of instabilities is observed, including viscous buckling, as the ratio of outer to inner flow rate is increased. We have mapped a phase diagram of flow types at various capillary number, and we will discuss the effects of expansion geometry, viscosity ratio, and Peclet number on the observed behavior.