Particle-laden drop impacting on solid surfaces

This paper presents an experimental study of the effects of particles on spreading and retracting of a single drop impacting on a smooth surface. The results are reported for particle concentrations from 0 to 0.30, different liquids (mixtures of water and glycerin), Reynolds number from 6.1 to 2700 Weber number from 0.0084 to 180, and four different surfaces (thermal oxide coated silicon wafer, silicon wafer, 1,1,1,3,3,3, hexamethyl disilazane (HMDS) coated silicon wafer, and Teflon(R) film). Drops laden with polystyrene particles coated with calcium phosphate are observed to behave differently from pure liquids, especially on thermal oxide coated silicon wafer, which is the most hydrophilic surface studied. It was found that pure fluid viscosity is more important than apparent viscosity of the particle-laden fluid in setting the spreading and retraction. At an impact speed of 2 m/sec, the rebound behavior on the Teflon(R) surface depends on particle volume fraction.