Liquid-Liquid Phase Separator for Synthesizing Gold Nanoparticles in Toluene

It is challenging to separate the immiscible liquid of low surface tension from water using the microfluidic device. This study presents a microfluidic chip composed of a T-junction, reaction channel and a novel liquid-liquid phase separator for continuously synthesizing fine gold nanoparticles in the organic solvent of toluene. The designed glass chip is used to separate two immiscible liquids via with the microfluidic channels of different depths. The surface tension and the capillary force differences are used to separate the two immiscible fluids. The stable segmented flow is initially produced by the T-junction and the gold salt is then reduced due at the reaction channel. The toluene with reduced AuNPs is finally collected via the designed separator downstream. Results show that the separator is capable for separating water (surface tension = 72.75 mN/m) and toluene (surface tension = 30.9 mN/m) with 92% separation efficiency. Results indicate that the gold nanoparticle (AuNPs) synthesized in the microdevice exhibits a narrower size distribution and better dispersion, comparing to the typical batch synthesis process. This study develops an efficient microfluidic system for stable chemical reaction and liquid-liquid phase separation in the microchannel.