Mass Dependence of Rolling/Slipping Ratio in Sliding Acceleration of Water Droplets on a Smooth Fluoroalkylsilane Coating

Using particle image velocimetry, we directly observed the internal fluidity of water droplets with various masses sliding on a smooth fluoroalkylsilane (FAS-17) coating. The water droplets slid downward with acceleration by a caterpillar-like rotation with slippage on the solid-liquid interface. The sliding acceleration of the advancing contact line was estimated using the combination of the accelerations of each motion. The contribution of rolling motion is large in the sliding acceleration of large droplets, and the smaller droplets slide down mainly with a slipping mechanism.