Vortex trapping and separation of particles in shear thinning fluids

Both enrichment and isolation of target particles from heterogeneous biological or chemical fluid samples are necessary steps in numerous particle-based analyses. We demonstrate, in this work, a vortex-based passive trapping and separation (by size) of particles in the flow of strongly shear thinning xanthan gum solution through a cavity microchannel. Our method utilizes the size-dependent fluid rheology- and inertia-induced lift forces that first align larger particles along the sidewalls of the straight uniform channel section and then drive them toward the microscale vortices developed inside the cavity because of the fluid shear thinning effect. It works effectively at the Reynolds number that is one order of magnitude smaller than the reported inertial vortex trapping for similar-sized particles. Our proposed particle trapping and sorting method in shear thinning fluids will be useful for applications processing medium-volume samples, which may fill the gap between the high-throughput inertial vortex...