Motion of liquid drops on an inclined solid surface

Abstract

The shape and motion of sliding drops on an inclined plane have been studied experimentally. In the experiments, various volumes of water, ink, ethylene glycol, and glycerin drops are placed on solid surfaces and the substrate is tilted to record the motion of the drops. A scaling law is provided to predict the steady-state velocity of the drop. It is shown that Poiseulle flow analysis cannot describe the steady-state motion of a drop. Instead, much stronger dissipation arising near the contact line is shown to play a major role in determining the speed of the drop. The scaling analysis agrees with experimental results using highly viscous liquid drops of ethylene glycol and glycerin. On the other hand, relatively inviscid drops of water and ink more slowly before abruptly accelerating to a high speed. This suggests that there exist two jumps in the dynamic state of those drops, one corresponding to initiation of movement and the other to a subsequent transition to a steady motion.