Static and dynamic behavior of water droplet on solid surfaces with pillar-type nanostructures from molecular dynamics simulation

Predicting the droplet state accurately is significant in manufacturing rough surfaces with superhydrophobic properties. We use molecular dynamics simulation to investigate the static behavior of the water droplet on solid surfaces featuring pillared structures. Results show that the droplet in either the Wenzel state or the Cassie state depends on the height of the pillars and the pillar surface fraction. We then apply a vibration to the smooth or rough surface and evaluate the dynamic behavior of the water droplet. In general, the smooth surface becomes more hydrophobic due to the presence of vibration and the water droplet on the pillared surface is able to transform from the Wenzel state to the Cassie state even though the former is originally favored. In addition, the vibration must meet certain conditions to achieve this transition and the droplet will separate from solid surface while continuing to enhance the vibration.