Modeling Nanoparticle Synthesis in Droplet-Flow Microreactors: Understanding Kinetic and Mass Transfer Effects

Droplet-based microfluidic systems offer a promising platform for controlled synthesis of nanoparticles with each droplet behaving as a microreactor with identical mixing characteristics. While experimental studies increasingly use droplet microreactors to fine-tune particle properties, most modeling efforts remain limited to single-phase systems. This study addresses this gap by developing a model for nanoparticle formation in two-phase droplet flows. Our model incorporates the coupled effect of reaction kinetics and interfacial mass transfer on the mean particle size and particle size distribution (PSD). The metal precursor and reducing agent are assumed to be confined to the dispersed(droplet) and continuous phases, respectively. This enables additional control over the nucleation and growth rates through interphase mass transfer. Using numerical simulations based on the population balance equation and Finke–Watzky two-step reaction mechanism, we investigate the effects of various parameters such as nucleation and growth rates and the diffusion coefficients on PSD. Specifically, increasing the diffusion coefficient in the continuous phase enhances the transport of the reducing agent, leading to smaller average particle sizes with minimal change in polydispersity. Additionally, higher nucleation rates favor smaller particles, while enhanced growth rates result in broader size distributions and larger diameters. This modeling framework bridges transport and reaction phenomena in droplet microreactors, offering predictive insights into optimizing nanoparticle synthesis.