Friction of sparkling water drops on superhydrophobic surfaces*

When a carbonated water drop is placed on an extremely water repellent, superhydrophobic surface, a microscopically thin gas cushion of carbon dioxide is formed under the drop. These levitating “fizzy” drops have an extreme mobility similar to that of Leidenfrost drops moving on their own vapor when placed on a very hot surface. Probing the friction and dynamics of levitating drops will provide new insights into extreme anti-wetting.

In our work, we have used micropipette force sensors to directly measure the minute friction force of levitating sparkling water drops moving on a transparent superhydrophobic substrate. Using reflection interference contrast microscopy, we have simultaneously measured the gas film thickness under the drop as a function of time. We have studied how the friction force scales with the film properties and drop dynamics. Our findings provide valuable experimental data of this fascinating ultra-slippery system.