MBE Research Highlights

Pancake bouncing: breaking the classical contact time limit of drop impinging on surfaces

Research Highlights - Dr. Zuankai Wang

The work on drop impact on superhydrophobic surfaces conducted in the lab of Bio-inspired Engineering, directed by Dr. Zuankai Wang’s in the MBE, was published in Nature Physics.

Brief Introduction

The study of drop impact is of scientific interest and has numerous practical applications. Recently, with the emergence of biomimetics and nanotechnology, numerous investigations have shown that drop can rebound off superhydrophobic surfaces owing to the negligible viscous dissipation enabled by the presence of trapped air pockets underlying the impinging drop. Until now it was generally believed that drop impacting on solid surfaces could always be separated into two phases: spreading and retracting. In the spreading phase, the drop undergoes an inertia-dominant acceleration and reaches a pancake shape. In the retraction phase, the drop minimizes its surface energy and finally takes off. For the first time, we reported the development of a novel surface made from an array of widely spaced tapered posts that enables the impinging drop to bounce off with a pancake-like shape without retracting [1]. This allows a fourfold reduction in contact time compared with conventional complete rebound. This work signifies a new direction in the field of drop impact and will find lots of potential applications. The work is also featured in the News and Views in Nature Physics [2].


  1. Yahua Liu, Lisa Moevius, Xinpeng Xu,Tiezheng Qian, Julia M Yeomans, Zuankai Wang. Pancake bouncing on superhydrophobic surfaces. Nature Physics, 10, 515-519 (2014)
  2. Doris Vollmer, Hans-Jürgen Butt, Fluid dynamics: Shaping drops, Nature Physics, 10, 475-476 (2014)

Selected press coverage:
(20 July 2014) CityU develops the world's most superhydrophobic material [CityU Press Release]
(21 July 2014) 城大研超疏水材料 可助飛機防積冰 [Oriental Daily]
(21 July 2014) 城大研新材料防機翼積冰 [The Sun]
(21 July 2014) 城大研發疏水性能最佳材料 [Hong Kong Commercial Daily]
(21 July 2014) 城大成功研發防積冰材料 [Hong Kong Daily News]
(21 July 2014) 城大超疏水材料 防飛機翼積冰 [Wen Wei Po]
(Jan 2015) New discovery for water repellent material [CityU Today Issue No. 47]

Last modified on 16 February, 2015