Directional Drop Rebound on Adhesive-Gradient Micro-Nanostructured Surfaces Formed by a Femtosecond Laser.

The dynamic behavior of droplets hitting a solid surface has received extensive attention due to its broad application prospects. Additionally, controlling the rebound behavior of impacting droplets is an important research topic. Current methods for investigating this behavior focus on the construction of a differentiated wettability surface, which is characterized by contact angle measurements, or a differentiated topography surface, which is represented by geometric height. This information allows one to obtain the nonuniform kinetic energy distribution of rebounding droplets and to realize control of rebounding droplet behavior. In this paper, femtosecond laser processing is proposed for the fabrication of an anisotropic surface with differences in adhesion, which allows for the control of impacting droplet rebound behavior. The experimental results show that the micro-nanostructure of the surface affects its adhesion. By changing the micro-nanostructure of the solid surface, the difference in surface adhesion can be controlled, thereby realizing precise control of impacting droplet rebound behavior. This study demonstrates that the micro-nanostructured surface formed by a femtosecond laser can be used to control a droplet rebound direction and landing site, which is of great significance to the development of liquid transport, microfluidic devices, and other fields.