Microfluidics has emerged in recent years as a versatile method of manipulating fluids at small length-scales, and in particular, offers a large range of deformation rates and direct visualization of resulting flow fields, providing an ideal platform for capturing the flow behavior of complex fluids in real time.

In this talk, I will showcase 2 simple microfluidic platforms with gelation and mixing applications.

(1) Wormlike micellar (WLM) solutions are frequently used as fracture and proppant-carrying fluids in enhanced oil and gas recovery applications in porous rock beds where complex microscopic geometries result in mixed flow kinematics with strong shear and extensional components. Shear-induced structures (SIS) are known to form in flows of wormlike micellar solutions. In simple shear cases these structures (SIS) are temporary and disintegrate upon cessation of the flow; while in certain mixed-flow cases these flow-induced structured phases (FISPs) are stable and long-lived. Here, we study the flow of micellar solutions in a microfluidic device containing an array of microposts and explore the gelation mechanism with encapsulation and biosensing applications.

(2) The ability of fluids to mix is greatly enhanced by turbulence, which occurs at large values of the Reynolds number. Small length scales tend to suppress Re, making it difficult to develop turbulent mixing in microfluidic devices. Improved understanding and characterization of stability conditions for flows through intersecting geometries is vital for the optimization of many laboratory microfluidic experiments and also practical lab-on-a-chip designs. We examine fluid flow through micro-cross-slot devices with various aspect ratios. We demonstrated that the steady spiral vortex instability observed for flow driven far from equilibrium above a critical Reynolds number in cross-slot devices, is well-described by a Landau model analogous to that used near equilibrium tricritical points.  Flow simulations indicate the instability is driven by vortex stretching at the stagnation point.