Droplet friction on superhydrophobic surfaces

Abstract The friction (lateral adhesion) of a sliding droplet on a solid substrate remains underexplored and the solid–liquid–vapor composite interfaces on superhydrophobic surfaces make droplet friction more complicated. This is because the microscopic contact line of the sliding droplet is anisotropic and nonsynchronous, which behaves and interacts with the surface microstructures distinctly everywhere along the apparent droplet boundary. Here, we customize an experimental setup to simultaneously measure the dynamics of the apparent droplet shape, macro‐ and microscopic contact line, and the friction force of a sliding droplet on pillared superhydrophobic surfaces with systematically varying dimensions. Stemming from the energy consumed by the sliding contact line and the distorted liquid–vapor interface, we develop an analytical model to predict the droplet friction force relying only on the droplet volume and micropillar dimensions.