Droplet fluid infusion into a dust layer in relation to self-cleaning

Wettability of a droplet liquid on a dusty hydrophobic plate is considered and the fluid infusion into the dust layer is studied pertinent to dust removal from the hydrophobic surfaces via rolling/sliding droplets. Influence of droplet hydrostatic pressure on the fluid infusion into dust layer is also investigated towards exploring the dust removal mechanisms. Environmental dust characteristics are evaluated and their interface with the droplet fluid is assessed. Sets of experiments are carried out to examine: (i) droplet fluid infusion into the dust layer, (ii) droplet fluid cloaking of dust, and (iii) evaluate the weight gain of the dust particles during cloaking. The findings reveal that droplet fluid (water) spreads onto the dusty surface and infuses on the dust particles. Cloaking velocity decays sharply with time and the weight gain of the dust particles is about 17% of the original dust weight after cloaking. The dust particles have a large area of nano-size open-pores-sites on the surface; however, capillary diffusion through these sites is limited with shallow depths and the weight gain of a dust particle via capillary diffusion is about 1% of the particle weight. The maximum infusion depth of the droplet fluid in the dust layer is about 74 μm, which is slightly less than the dust layer thickness on the surface. The rolling droplet picks up all the dust from the 150 μm thick dust layer on the surface.