High speed microturbine mixer for kinetically controlled synthesis

The design, fabrication, simulation, and experimental characterization of a microfabricated, fluidically-driven microturbine mixer are presented. The mixer was engineered to achieve rapid mixing (<1 ms), enabling control over kinetically-limited chemical reactions. The microturbine is microfabricated in silicon using a sequence of photolithographic patterning and deep reactive ion etching (DRIE) steps. The device features two fluidic inlets, each supplying chemical reagents, that drive a microturbine through momentum transfer, generating shear forces within the reaction chamber to induce mixing. By systematically varying the flow rates of the reagents, the rotational velocities of the microturbine were experimentally and computationally determined. Mixing profiles were analyzed using fluorescence colocalization, an established biological imaging technique that was adopted for this application. Characterization results were leveraged to optimize the synthesis of ultra-small, monodisperse silver nanoparticles (AgNPs), i.e. particles of 1 nm to 3 nm in diameter. These nanoparticles have very large surface-to-volume ratios, making them ideal candidates for applications in catalysis, sensing, and antimicrobial agents. The microturbine mixer provides a scalable and reproducible method for the production of ultra-small AgNPs through precise control of mixing conditions, overcoming challenges associated with traditional synthesis routes that struggle to attain size control, size distribution and reproducibility.