Experimental and Computational Analysis of Mixing Inside Droplets for Microfluidic Fabrication of Gold Nanoparticles

Abstract

Emulsions formed by mixing reactant streams inside microdroplets are efficient microscale reactors for the synthesis of nano/microparticles/crystals due to small quantities of reagents confined within each droplet and the separation of droplet contents from the reactor walls. In this work, the synthesis of size-tunable gold nanoparticles (AuNPs) within emulsion droplets generated in a three-phase glass capillary microfluidic device was investigated experimentally and numerically using computational fluid dynamics (CFD). AuNPs were produced by micromixing two aqueous streams, 1.15 mM HAuCl 4 containing the 1% poly(vinylpyrrolidone) capping agent and 20 mM ascorbic acid solutions, inside monodispersed droplets created by three-dimensional (3D) counter-current flow focusing in a medium-chain triglyceride. The mean particle size of AuNPs was tunable in the range between 26 and 56 nm and depended on the degree of premixing of the reactant streams shortly before droplet generation, and the mixing efficiency within droplets, which was controlled by hydrodynamic conditions within the microfluidic device. The CFD results were compared and validated against experimental observations and revealed the presence of a recirculation zone near the outer wall of the injection capillary tip. The mixing efficiency was higher at smaller droplet size causing a reduction in the particle size of the AuNPs.

Recent Progress of Droplet Microfluidic Emulsification Based Synthesis of Functional Microparticles

“…Due to the good biocompatibility of gold nanoparticles, they have attracted the considerable attention in the field of application, and the demand has increased dramatically. [ 116 ] Wagner and Köhler [ 117 ] have developed a sandwich (glass–silicon–glass) structure for the synthesis of gold nanoparticles with 5–50 µm. In order to avoid the deposition of the generated particles on the inner wall, Duraiswamy and Khan [ 118 ] ingeniously designed a PDMS‐based droplet microfluidic device to suspend the prepared particles in the oily continuous phase (Figure 6e ).…”

Continuous Electroformation of Gold Nanoparticles in Nanoliter Droplet Reactors

“…Serving as individual reactors, droplets provide a reproducible environment, where the reaction conditions can be precisely tailored. This has been demonstrated for the synthesis of metal nanoparticles, [16,29,30] metal oxide particles, [31] metal-organic frameworks, [32] and quantum dots. [33] Studies combining the advantages of electrochemical synthesis with nanoliter droplet reactors have focused on the deposition of nanostructures at the liquid-liquid interface of non-confined droplets.…”

“…Serving as individual reactors, droplets provide a reproducible environment, where the reaction conditions can be precisely tailored. This has been demonstrated for the synthesis of metal nanoparticles,[ 16 , 29 , 30 ] metal oxide particles, [31] metal–organic frameworks, [32] and quantum dots. [33] …”

Kontinuierliche Elektrochemische Synthese von Gold‐Nanopartikeln in Nanoliter‐Reaktoren

“…Die Tröpfchen dienen dabei als individuelle Reaktoren und bieten eine reproduzierbare Umgebung, in der die Reaktionsbedingungen genau abgestimmt werden können. Dieses wurde für die Synthese von Metall-Nanopartikeln, [16,29,30] Metalloxidpartikeln, [31] metallorganische Verbindungen, [32] and Quantenpunkten [33] gezeigt.…”