Effect of micro-impeller geometries on mixing in a continuous flow active microreactor

• Mixing efficiency of different geometries of microimpeller was studied in a continuous flow active microreactor. • Simulation studies for different geometries of microimpeller in fluid mixing was studied. • Mixing efficiency of different geometiries of microimpller was demonstrated experimentally. • Application of rhombus microimpeller was demonstrated by synthesizing Prussian blue nanoparticles. Microreactors are widely reported for performing chemical reactions of all kinds. Chemical reactions should possess attributes like complete mixing with a faster rate to obtain a high-quality product. Usually, microreactors mix the liquid passively and thus suffer from slow mixing rates due to longer channels. Moreover, it is challenging to achieve complete mixing of fluids in passive microreactors as they are predominantly diffusion dependent. An active microreactor is suitable to enhance the rate of mixing and its efficiency. In the present work, we have utilized the magnetic field to rotate a micro-impeller in an active microreactor. The active microreactor and micro-impellers (iron oxide nanoparticles embedded in PDMS matrix) of various geometry (triangle, square, rectangle, and rhombus) were fabricated using soft lithography. These differently shaped micro-impellers were evaluated theoretically and experimentally for mixing in a continuous flow active microreactor. Simulation studies using Comsol Multiphysics revealed approximately equivalent mixing efficiency for all the shapes; however, rhombus micro-impeller excelled. Further, experimental studies showed better mixing efficiency of rhombus micro-impeller as compared to other micro-impellers. 97% mixing efficiency for rhombus micro-impeller can be attributed to the shape and its stability in continuous flow. Finally, the rhombus micro-impeller was used to synthesize Prussian blue nanoparticles in a continuous flow active microreactor.