(349g) Convective Flows Driven By Solute Gradients in Microfluidic Channels

We developed a microfluidic system for the direct visualization and measurement of circulating buoyancy-driven flows driven by externally applied concentration gradients. We show that such flows exhibit velocities comparable to those due to diffusiophoresis, osmophoresis, and chemotaxis but are often overlooked in studies of colloidal motion in concentration gradients. We present a model to describe how such buoyancy-driven flows are determined by the concentration gradient, solute type, solution viscosity, and height of the microfluidic channel. The model is validated quantitatively by comparison to experimental measurements of colloidal motion in steady solute gradients under a variety of conditions. These results are useful in identifying and minimizing undesired buoyancy-driven flows within microfluidic systems; alternatively, we show how these flows can be harnessed for useful functions such as size-based particle sorting.