Effect of viscosity on surface acoustic wave driven collective particle dynamics in sessile droplets: nebula, black holes and white dwarfs

Abstract

In this paper, we experimentally investigate the effect of particle diameters (20 nm, 100 nm, 450 nm, 1 µm, 5 µm and 10 µm) and liquid viscosity (0.892 mPa.s, 5 mPa.s, 18.1 mPa.s, 45.4 mPa.s and 156 mPa.s) for particle concentration and accretion by acoustic vortex with topological charge = −15 in the sessile droplets. Three very interesting aggregation states are experimentally observed: Nebula, Black Hole and White Dwarf. In the experiments, we successfully concentrate particles with diameters smaller than 20 nm to a cloudy state and aggregate 5 µm and 10 µm particles to a spot. It is worth noting that we find a state of particle concentrating in most cases of our experimental conditions is a black hole will appear in the sessile droplet and the capture radius (Black Hole radius) is directly affected by particle size and liquid viscosity.