Oscillation behaviors of oil droplets adhered on the solid surfaces with different wettability in a laminar flow field

The oscillation of oil droplets on surfaces with different wettability in laminar flow field affected the initial movement behaviors of oil droplets, which was studied experimentally and theoretically in the paper. In the initial oscillation stage, the contact line of the oil drop on the substrate did not move, while the center mass and contact angle hysteresis of the droplet have changed. It was found that there were two oscillation patterns for adhered oil drop in the flow water, one was the up-down oscillation, the other was left-right oscillation, which can be transformed into each other. The contact angle evolution of oscillating oil drop was analyzed. It was found that with the increase of water flow velocity, the difference between the maximum and minimum contact angles of adhered oil drops on different surfaces was increasing, and the contact angle of oil drops on oleophobic surfaces underwater was more likely to exceed the advancing contact angle during the oscillation process. The force analysis of the three-phase contact point of the oil drop on the surfaces was carried out, and the oscillation behaviors of the oil drop were explained theoretically. The sensitivity analysis of the factors affecting the oil drop oscillation behaviors was carried out, and the influences of the oil drop height and the surface wettability on the oil drop oscillation frequency and amplitude was obtained.