(369b) Controlling Metal Nanoparticle Size Distribution through Microreactor Residence Time Distribution

The application of microreactors for nanoparticle synthesis has been widely studied and commercially implemented for applications in vaccine manufacturing and drug delivery. Because of their small length scale, microreactors systems offer the potential to achieve rapid convective mass transport in a fraction of seconds. This allows control of the nucleation and growth kinetics of nanoparticles. Besides mixing, nanoparticle size distribution is also affected by the residence time distribution of the reactor [1]. Conventional microreactor designs, including T-mixer and jet mixing reactor designs typically yield a laminar flow profile. Radial mixing under laminar conditions is limited to diffusion, leading to a broad residence time distribution (RTD) of particles inside the reactor. Longer residence time inside the reactor allows existing nanoparticles to grow, widening the particle size distribution. A polydisperse nanoparticle distribution compromises the uniformity of size-dependent nanoparticle properties such as fluorescence, catalytic activity, and surface plasmon resonance. A clear understanding of the RTD effect on product functionality is lacking. Hence, this research aims to investigate the effect of microreactor design on the RTD and a model nanoparticle system.

Our strategy involves producing nanoparticles using a jet mixing reactor (JMR) microreactor. The JMR is a three inlet microreactor, with two cross-flow jet streams impinging on a central main fluid stream. Two variants of JMR outlet designs were probed: (a) a curved helical outlet, and (b) a straight outlet. JMR RTDs were probed using a step input of rhodamine B tracer dye. The outlet solution absorbance was monitored at 565 nm using flow cells to compute the mean, variance, and skew of the RTD curve. The Villermaux-Dushman competitive reaction set was used to investigate the effect of mixing time for straight vs. curved outlets. Further insights into JMR mixing and RTD were found through COMSOL simulations. Gold nanoparticles were selected as the model reaction system due to their size-dependent surface plasmon resonance properties. The effect of RTD and inlet flow rates on nanoparticle size distribution was analyzed using transmission electron microscopy. Polydispersity index served as the evaluation criteria for JMR synthesis with curved versus straight outlets.

References:

[1] Gao, Yunhu, Bruno Pinho, and Laura Torrente-Murciano. "Tailoring the size of silver nanoparticles by controlling mixing in microreactors." Chemical Engineering Journal 432 (2022): 134112.