Water super-repellent behavior of semicircular micro/nanostructured surfaces

Abstract

In this article, we report the construction of semicircular micro/nanostructured surfaces. Based on thermodynamic analysis, free energy (FE) and free energy barrier (FEB) as well as equilibrium contact angle (ECA) and contact angle hysteresis (CAH) for four exact wetting states of semicircular micro/nanostructured surfaces are theoretically discussed in detail. Notably, the wetting behavior is closely related to the exact wetting state and the base radius or space of semicircular micro/nanostructure. Furthermore, it is demonstrated that the stable wetting state of the semicircular micro/nanostructured surfaces depends on the microscale and nanoscale ratio of base space and radius. A suitable semicircular micro/nanostructure of the surface may lead to a droplet in the stable Cassie–Cassie (Cc) state. Moreover, an important role of the nanoscale semicircular surfaces in determining water super-repellence is effective in decreasing or increasing the ratio of microscale base space and radius for the Cassie or Wenzel state. Additionally, wetting behaviour of single semicircular micro- and nano-structured surfaces are comparatively investigated. The FE and ECA of micro/nanostructured surfaces are lower or higher than those of the single microstructured surfaces. However, the effects of nanoscale semicircular surfaces on the FEB and CAH mainly rely on the microscale wetting state. Finally, the related experimental results were used to verify our investigation. These results are in good agreement with the experiment, which are helpful in designing the wetting behavior of hierarchical semicircular micro/nano-structured surface.