Designing Patterned Wetting Surfaces for Multiple Applications

Abstract

Inspired by natural surfaces on the lotus leaf, fish skin, tillandsia, springtail and pitcher plant, functional materials and surfaces with special wettability have been substantially engineered such as superhydrophobic (SHB), superhydrophilic (SHL), superoleophobic (SOB) and superoleophilic (SOL) surfaces, as well as slippery liquid-infused porous surface (SLIPS). More importantly, elegantly patterning two or more of these wettability characteristics on a single surface provides a promising strategy to create multifunctional wettability-patterned surfaces. Such patterned wetting surfaces play an increasingly important role in a wide variety of applications ranging from microfluidics, water treatment, tissue engineering, and cell biology to drug delivery. Although the advantages of functional surfaces with a patterned wettability feature in various applications have been unveiled over the past two decades, more explorations are still required to reveal superior functionalities of patterned wetting surfaces in engineering applications. Herein, this thesis is aimed to design and prepare the patterned SHL-SHB surface, patterned SLIPS-SOB surface, as well as patterned slippery surface, and investigate their potential performances in the fields of underwater adhesion, droplet manipulation, and hydrodynamic energy harvesting.

In the first section, we designed and fabricated a patterned SHL-SHB surface by engineering SHB and SHL patterns on an aluminum substrate, which achieves a reversible adhesion underwater. On one hand, underwater adhesion is achieved through the capillary cooperation of SHB and SHL regions, wherein the air film trapped in the SHB regions blocks the connection between the water inside the SHL regions and the external water environment. On the other hand, when a direct current is connected to the patterned SHL-SHB samples, the electrolysis of water occurs inside the samples and generates large numbers of bubbles, which causes the pressure change in the SHB regions and realizes the separation of the sample. Therefore, reversible adhesion underwater can be achieved.

In the second section, we replaced the SHL region by SLIPS region to create a patterned SLIPS-SOB surface to solve the problems existing in patterned SHL-SHB surfaces. Through designing and preparing different patterned SLIPS-SOB surfaces, the directional and lossless transportation of water, and the collision of water droplets on such surfaces can be precisely manipulated.

In the final section, we developed a new type of water electricity generator by combining smooth dielectric materials exhibiting super slippery property and slippery aluminum electrode on the same surface. The falling water droplets can spread on both the dielectric material and electrode surfaces, which renders the originally disconnected components into a closed electrical system and transforms the conventional interfacial effect into a bulk effect. Based on such structural design, we prepared two forms of electricity generators, one was an open device supplied by water sources such as raindrops and waves in nature, and the other was a closed device driven by external energy input. Both two forms of electricity generators allow for the reversible and efficient transfer of charges in closed electrical system, resulting in the improvement of power density by several orders of magnitude over its counterparts imposed by the interfacial effect.

Date of Award	24 Dec 2020
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Zuankai WANG (Supervisor)