Analysis of complex spiral vortex field in nano particle concentration

A strategy to concentrate nanoscale particles on the interface between a nano suspension droplet and non-vibration substrate is demonstrated and analyzed. It employs the spiral vortex of acoustic streaming, generated by an ultrasonically vibrating needle parallel to and above the non-vibration substrate. The vortex drags nanoscale particles to the center of itself, forming a concentration spot. For 250 nm-diameter SiO
₂
nano particle suspension with an initial concentration of 0.09 mg/ml, the diameter of the concentration spot can be up to several hundred microns. The dependency of the spiral vortex field on the vibration distribution of the acoustic needle immersed in the droplet is also clarified by experiments and simulation of the COMSOL Multiphysics FEM software, and the concentration conditions are obtained by analyzing the nano particle dynamics in the spiral vortex.