Bidirectional Droplet Motion
The self-propulsion of liquid droplets on surfaces with chemical or topographical wetting gradients is usually one-directional, as seen here. However, bidirectional droplet motion is made possible using liquid infused surfaces with topographical gradients. On these surfaces, a deposited droplet can move either toward the denser or the sparser areas. The key factor determining the direction of motion is the wettability difference of the droplet on the solid surface and on the lubricant film.
The video below shows the motion of a droplet on a liquid infused surface with a linear topographical gradient.
The next video shows motion of a droplet on a liquid infused surface with a stepwise gradient and negative
driving force.
The final video shows the motion of a droplet on a liquid infused surface with stepwise gradient and positive driving force.
The videos above are from the Supplementary Information of the publication listed at the end of this page.
Publication
Bidirectional motion of droplets on gradient liquid infused surfaces, M.S. Sadullah, G. Launay, J. Parle, R. Ledesma-Aguilar, Y. Gizaw, G. McHale, G.G. Wells and H. Kusumaatmaja, Communications Physics 3 (2020), 166