Cadmium Sulfide Nanoparticle Synthesis Using Oscillatory Flow Mixing

Microchannel mixers enable faster mixing times compared with batch stir mixing leading to the promise of higher throughput, better yields and less solvent usage for the solution-phase reactive precipitation of inorganic nanoparticles. However, reliance on diffusive transport for subsecond mixing requires channel dimensions in the tens of micrometers. These channel dimensions make diffusive micromixers vulnerable to clogging. In this paper, an oscillatory flow mixing strategy is explored to increase the contact area between reagents within larger microchannels. Forward and reverse oscillatory signals are designed to pump reactants through a 450 μm high serpentine microchannel to increase advection within the flow. Computational fluid dynamics simulations are performed to provide insight into flow behavior and nanoparticle morphology. Quantification of mixing performance is proposed using mixing quality and particle residence time metrics. Experimental validation is pursued through the reactive precipitation of CdS quantum dots using a reverse oscillatory mixing setup. Transmission electron microscopy provides insights into the particle size distribution and particle crystallinity.