Mixing enhancement induced by viscoelastic micromotors in microfluidic platforms

Fine manipulation of fluid flows at the microscale has a tremendous impact on mass transport phenomena of chemical and biological processes inside microfluidic platforms. Fluid mixing in the laminar flow regime at low Reynolds number is poorly effective due to the inherently slow diffusive mechanism. As a strategy to enhance mixing and prompt mass transport, here, we focus on polyelectrolyte multilayer capsules (PMCs), embodying a catalytic polyoxometalate, as microobjects to create elastic turbulence and as micromotors to generate chaotic flows by fuel-fed propulsions. The effects of the elastic turbolence and of the artificial propulsion on some basic flow parameters, such as pressure and volumetric flow rate, are studied by a microfluidic set-up including pressure and flow sensors. Numerical-handling and physical models of the experimental data are presented and discussed to explain the measured dependence of the pressure drop on the flow rate in presence of the PMCs. As a practical outcome of the study, a strong decrease of the mixing time in a serpentine microreactor is demonstrated. Unlike our previous reports dealing with capillarity flow studies, the present paper relies on hydrodynamic pumping experiments, that allow us to both develop a theoretical model for the understanding of the involved phenomena and demonstrate a successful microfluidic mixing application. All of this is relevant in the perspective of developing microobject-based methods to overcome microscale processes purely dominated by diffusion with potential improvements of mass trasport in microfluidic platforms.