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Enhanced droplet mobility on superwetting surfaces
* 1 , 2
1  School of Mechanical Engineering, Dalian University of Technology
2  Department of Mechanical and Biomedical Engineering, City University of Hong Kong


Water droplets impacting onto solid surfaces give rise to a broad diversity of fascinating physical phenomena including “crown formation”, jetting of secondary droplets and splashing. Due to the discovery of micro/nanostructured surfaces, the physics of droplet impact has been greatly enriched. An impacting droplet can exhibit wetting, pinning, partial rebound and complete rebound resulting from the generation of special wetting states at different impact conditions. Notably, the investigation of enhanced droplet mobility upon superwetting substrates is directly relevant to a wide range of applications, such as anti-icing, water-repellency or water-harvesting, anti-bacterial coatings and phase change heat transfer. In this talk, I will briefly discuss our recent efforts and exciting progress to this important problem. By designing novel surface made from an array of widely spaced tapered posts, the impinging droplet can bounce off with a pancake-like shape without retracting, leading to a fourfold reduction in contact time compared with conventional complete rebound. Then, I will discuss an asymmetric bouncing on cylindrical surfaces with a convex/concave architecture of size comparable to that of the drop, which leads to a 40% reduction in the total contact time. I will also discuss a new bouncing regime that combines the inherent advantage of lotus leaves and pitcher plant surfaces. We find that there exists a superhydrophobic-like bouncing on thin liquid films, characterized by the contact time, the spreading dynamics, and the restitution coefficient independent of the underlying liquid substrate. Finally, I will discuss the break of wetting symmetry of a droplet at high temperature by creating two concurrent thermal states (Leidenfrost and contact-boiling) on patterned surfaces, and thus engendering a preferential motion of a droplet towards the region with a higher heat transfer coefficient.

Keywords: superwetting surface, pancake bouncing, asymmetric bouncing, superhydrophobic-like bouncing, Leidenfrost