Rebecca Dylla-Spears1, Joo Sung Lee2, Joanne dela Cruz1, Kevin Yuan1, and Susan J. Muller1. (1) Chemical Engineering, University of California at Berkeley, Berkeley, CA 94720, (2) Information Technology & Electronic Materials R&D, LG Chem Research Park, South Korea
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 (η2 << η1). 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.