Droplet directional movement on the homogeneously structured superhydrophobic surface with the gradient non-wettability

Surface with the gradient non-wettability intensely appeals to researchers due to its academic significance and applications for directional droplet movement. Herein, we developed a homogeneous structure superhydrophobic surface with the gradient non-wettability by a combination strategy of chemical etching and vapor diffusion modification. As a consequence, the as-prepared surface exhibits a remarkable gradient characteristic of water repellency, and the water contact angle mainly locates within the range from 162°±0.5° to 149°±0.4°. Meanwhile, the sliding angle also exhibits a corresponding change from 3° to 11°. On this basis, the gradient characteristic of non-wettability induces the distinguishing droplet adhesion on the surface, i.e., from 19 μN for the most hydrophobic end to 57 μN for the opposite one. Due to the difference of water adhesion force, droplets on the as-prepared surface can well roll alongside a specific direction (i.e., gradient direction of non-wettability). In terms of dynamic imp...