Regimes of Spreading of a Water Droplet Over Substrates with Varying Wettability

Abstract

The authors have presented the results of experimental investigations into the physical mechanisms of change in the dynamic angle of contact of a droplet of distilled water on a substrate under the conditions of its wetting at high velocities of motion of the three-phase contact line. The investigations were carried out on three copper substrates and one superhydrophobic substrate. The authors have singled out three regimes of spreading of the droplet on the copper substrates with different surface roughnesses: formation of a droplet, spreading of the droplet, and formation of an equilibrium angle of contact. A distinctive feature of the droplet spreading over the surface with a superhydrophobic coating has been revealed, which lies in the monotonic increase in the advancing dynamic contact angle. The influence of the volume rate of formation of a droplet on the value of the dynamic contact angle has been established. On the copper surfaces with roughnesses of 5.190 and 6.210 μm, increase in the rate tended to increase the maximum value of the contact inflow wetting angle. However, on the copper surface with a roughness of 0.591 μm, the dynamic contact angle was independent of the droplet′s volume in the range of volume rates of droplet growth 0.040–0.160 ml/s.