Particle manipulation using variable body-curvature viscous streaming in microfluidic devices

Viscous streaming refers to the rectified, steady flows that emerge when a liquid oscillates around an immersed micro-feature, typically a solid body or a bubble. The ability of such features to locally concentrate energy and stresses that produce strong inertial effects to which both the fluid and suspended particles respond within short length and time scales, rendering viscous streaming arguably the most efficient mechanism to exploit inertia at the microscale. Despite this potential, viscous streaming has been investigated in rather narrow conditions, mostly making use of bodies of uniform curvature (cylinders and spheres) for which the induced flow topologies are limited. Here, we demonstrate that a variable body-curvature approach in viscous streaming dramatically extends the range of accessible flow topologies and enables novel applications for particle manipulation. We show for the first time that numerically predicted streaming flows can be physically reproduced in microfluidic chambers. We demonstrate how these newly accessible flow topologies are used to enhance particle manipulation, such as filtering and separation, in compact, robust, tunable, and inexpensive microfluidic devices.