(483i) Passive Separation of a Polydispersed Emulsion in a Microfluidic Channel

Studying therapeutic material in the pharmaceutical products can often be done using drop flow in a microfluidic device. Drops are commonly sorted through the utilization of active-sorting mechanisms such as electric, magnetic, or acoustic fields applied to separate particles flowing through a microfluidic device. However, active methods of separation can be difficult to integrate into a device. Deformable nano and microparticles experience demixing and segregation via passive transport in pressure-driven flows, due to effects such as wall migration, hydrodynamic diffusivity, and migration down shear gradients. Emulsion drop deformability can be controlled by the surfactant concentration used in the drop formation process. Monodispersed emulsion flows have been studied extensively both experimentally and theoretically. Despite much recent interest in passive hydrodynamic phenomena and their contribution to de-mixing in polydisperse suspensions such as blood, demixing in polydispersed emulsions has not been studied as thoroughly. In this talk we investigate passive separation in a polydispersed emulsion of mineral oil in water flowing through a Hele-Shaw channel at low Reynolds number. The emulsion drops were fabricated by mixing mineral oil in DI water with added cetyl trimethylammonium bromide (CTAB) as a stabilizer. The drops range from 2 to 3 µm in radius, but with a Poisson size distribution. A syringe pump is used to control the flow of the emulsion through a single straight microfluidic channel fabricated in polydimethylsioloxane (PDMS). We use particle tracking algorithms to track drop trajectories, measure velocities, and locate the drops in the direction of shear. Analysis of the emulsion flow finds that the largest drops flow in the center of the channel, causing the smaller drops to flow near the wall of the channel. Interestingly, even though the largest size drops constitute the smallest fraction of the total population, they greatly affect the margination of the smaller drops. To further explore this phenomenon, we investigate passive separation of drops with the addition of trace amounts of larger hard spheres.