Sliding behavior of water droplet on superhydrophobic surface

We found experimentally that the advancing contact angles on micropillar-like superhydrophobic surfaces are hardly affected by the fraction of the water-solid interface area, while the receding contact angles and the sliding angles are strongly influenced by this geometrical parameter. Different from previous works, using particle image velocimetry (PIV) and particle tracking velocimetry (PTV) techniques, both rolling and slipping motions were observed for 5 μL water droplet during its sliding-down. We revealed that the rolling only occurs at the edge of the water droplet and the slip velocity is higher than the rolling velocity due to the low viscosity of water.