Silica Synthesis and Coating of Quantum Dots in Droplet Based Microreactors

We present a microfluidic reactor that utilizes meandering microchannel shape to mix reagents inside droplets in a carrier fluid to synthesize silica and silica coated nanoparticles. Meandering channels decrease mixing time due to reduced diffusion lengths. Moreover, droplet-based flow provides uniform reaction times due to the circulating flow profile inside droplets as opposed to parabolic flow profile in straight channels. Before fabricating our device, we have simulated the mixing performance of droplets at different channel cross-sections and meandering geometries using Comsol Multiphysics^©. As a result, we have concluded that channel cross-section and meandering dimensions should be as small as possible for faster mixing. Accordingly, we have fabricated our device in PDMS by using soft lithography technique and introduced chemicals to the microsystem by using syringe pumps. We will use this system to understand the effect of solvent concentration and residence time on silica formation to obtain better coating thickness distribution than in batch-wise methods. As a preliminary study, we tested the silica formation inside droplets and we obtained 102 nm ± 4 nm of silica nanoparticles. In the synthesis we followed a modified method of synthesis in the literature where droplets of solution composed of 20 mL Cyclohexane, 2.6 mL IGEPAL and 300 μL TEOS were formed inside the carrier fluid NH₄OH at a flow rate ratio of 2:1. It is observed that nanoparticles were synthesized as a result of diffusion and mixing of NH₄OH inside droplets. Currently, we are working on introducing QDs in droplets and coating them with silica shells inside the microreactor. We will also study the effects of NH₄OH concentration, residence time on silica shell thickness and compare with batch-wise silica synthesis and coating of quantum dots and present these results at the conference.