Strategy for the improvement of mixing in microdevices

One of the most promising way to exploit microfluidic systems is as microreactors. A microreactor can be considered as a microchamber where chemical reactions take place, aimed at the synthesis of novel materials with controlled experimental conditions. The main goal is to reach the highest efficiency towards the desired output product. Mixing is usually very slow in microchannels, when laminar flow conditions characterized by low Reynolds numbers (below 3000) are applied. Many different strategies can be proposed to enhance mixing. In this work we explore and model the behavior of microreactor prototypes having different geometry and aimed at the improvement of mixing efficiency. These prototypes exploit either the hydrodynamic focusing effect or the presence of microstructuration inside the microchannel. In the first case, the focusing effect is used to reduce the diffusion distance between the molecules flowing in the reactors. In the second approach, we explore the influence of lateral steps fabricated inside the channels on the mixing efficiency. The behavior of fluid features is numerically modeled via Navier-Stokes equations coupled to convection-diffusion equations. Moreover, fluorescence based techniques are used to characterize the mixing efficiency in the experimental devices