Synthesis of narrow sized silver nanoparticles in the absence of capping ligands in helical microreactors

Abstract

Microtubular helical reactors generate secondary flows promoting the synthesis of mono-sized silver nanoparticles in the absence of capping ligands. This paper demonstrates the critical effect of the curvature of microreactors on the size distribution of silver nanoparticles during their continuous synthesis in the absence of capping ligands. By a combination of experimental data and deep understanding of the fluid dynamics inside the reactor, we demonstrate that decreasing the helix diameter of the reactor promotes the onset of transversal flows and radial mixing in helical reactors. These secondary flows enable fast nucleation and homogeneous growth during the synthesis leading to a delicate control of the particle size distribution. A similar effect is achieved by increasing the total flow rate, assuming that the Dean number is above ∼5, while no effect of the pitch distance within the experimental range on the size distribution is observed. These results will directly impact the nanomaterial field and the development of manufacturing routes as the size of the nanoparticles is known to play a key role in determining their chemical and physical properties.