Two microfluidic chips based on Rayleigh surface acoustic waves for controllable synthesis of silver nanoparticles: A comparison

Based on the biocompatibility and non-invasive nature of acoustically driven microfluidics, two microfluidic chips with Rayleigh surface acoustic waves (SAWs) as the driving source are proposed for micro-scale mixing: traveling surface acoustic wave (TSAW) and standing surface acoustic wave (SSAW) chips. This paper presents the first comparison of the controllable synthesis of silver nanoparticles (AgNPs) by TSAW chip and SSAW chip. The effect of peak-to-peak voltage and inlet flow rate on the micro-mixing performance of the two chips is investigated in focus. First, based on the finite element theory, the simulation software COMSOL is used to compare and analyze the mixing performance of the two chips. Then, a series of experiments of AgNPs synthesis is carried out combining with the liquid-phase reduction method. The difference in the results is characterized by UV spectroscopy and transmission electron microscope(TEM). The simulation results reveal that, under the same conditions, the SSAW chip transmits more energy to the fluid, which can effectively disturb the fluid and destroy the laminar flow interface. That is, it is easier to achieve rapid and uniform mixing with a better micro-mixing effect. As the peak-to-peak voltage increases or the inlet flow rate relatively decreases, the mixing effect of the SSAW chip gradually becomes better. However, experimental results indicate that the TSAW chip can synthesize AgNPs with higher concentration, better monodispersity, and smaller size deviation. As the peak-to-peak voltage increases or the inlet flow rate relatively decreases, it is easier to synthesize AgNPs with better quality. The comparison of the simulation and experimental results of the two chips can provide guidelines for the analysis of micro-scale mixing performance and practical applications of microfluidic chips driven by SAWs.