Lecture: Bio-inspired Interfacial Materials: From Fundamental Science to Multifunctional Applications 

Lecturer: Associate Prof. Zuankai Wang, Department of Mechanical and Biomedical Engineering, City University of Hong Kong 

Time: 3:00 pm, Aug 6, 2015 

Location: Meeting Room 211 of Administration Building 

Introduction of Lecturer 

Zuankai Wang is currently an associate professor in the Department of Mechanical and Biomedical Engineering at the City University of Hong Kong. He earned his Ph.D. degree in the Department of Mechanical, Aerospace and Nuclear Engineering at Rensselaer Polytechnic Institute in August 2008. After one year post-doctoral training in the Department of Biomedical Engineering at Columbia University, he joined the Department of Mechanical and Biomedical Engineering at the City University of Hong Kong as an assistant professor. Dr. Wang won the Chinese Government Outstanding Self-Financed Students Abroad Award in 2007, Best Paper Award in the Second and Third International Symposium on Optofluidics (2012, 2013), Materials Research Society Graduate Student Silver Award in the 2007 Fall Meeting and 2015 Spring Meeting (His PhD student: Yahua Liu).  In the past four years, he has published many papers as the corresponding authors in leading journals such as Nature Physics, Nature Communications, Physical Review Letters, ACS Nano, Advanced Functional Materials, Small, to name a few. 

Wang's homepage: http://www.cityu.edu.hk/mbe/zuanwang/

Lecture Abstract 

Nature has long provided unlimited source of inspiration for engineers. Indeed, many biological systems in nature orchestrate a high level of functionalities and adaptability to their environments enabled by intricate control of solid-liquid-vapor interfaces, for example self-cleaning lotus leaves and insect-capturing pitcher plant. The fundamental understanding and our ability to control those interfaces have transformative effects on some of the emerging challenges facing us. 

One central question in the emerging field of bio-inspired surfaces for multifunctional applications is the maximization of water repellency or the minimization of the contact time of a droplet with solid surface. However, there exists a theoretical contact time limit which is imposed by the classical hydrodynamics. In this talk, I will briefly discuss our recent efforts and exciting progress to this classical and 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. Our approach signifies a new direction in the design of bio-inspired materials for various applications. 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 discussa 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 thinliquid films, characterized by the contact time, the spreading dynamics, and the restitution coefficient independent ofthe underlying liquid substrate. Through experimental exploration and theoretical analysis, we demonstrate that the sustenance of such substrate-independent (superhydrophobic-like) bouncing necessitates an intricate interplay between the Weber number, and the thickness and viscosity of the liquid substrate.  

Finally, I will discuss how to translate the fundamental insights learned from the quest for the maximum water repellency to multifunctional applications including dropwise condensation, anti-icing, boiling heat transfer and fast droplet manipulation for optical imaging.