Active mixing with Quincke rollers

The mixing of fluids at the microscopic scale is a notoriously complicated problem due to flow reversibility at low Reynolds numbers. Different approaches have been used in the past, such as micromixers shaped in specific ways to induce chaotic flow curves, or passive particles under shear.

In this talk, I describe our efforts to mix fluids with a model active matter: Quincke rollers. They are micron sized insulating spheres that, when immersed in a conductive fluid and subjected to an external electric field, spontaneously rotate. Since they are settled on the bottom of a microfluidic cell, this rotation converts into a translation that can reach speeds of about 1 mm/s.

We are building an experimental system that will allow us to track the Quincke rollers while simultaneously characterizing the fluid mixing. By first characterizing the effect of a single roller as it stretches the fluid, then considering the system as a whole, we hope to show that the mixing dynamics are greatly enhanced by the particles movement. An order of magnitude calculation shows that the Quincke rollers could divide the mixing time by at least 200 when compared to a purely diffusive case.