Liquid repellency enhancement through flexible microstructures

Abstract

Artificial liquid-repellent surfaces have attracted substantial scientific and industrial attention with a focus on creating functional topological features; however, the role of the underlying structures has been overlooked. Recent developments in micro-nanofabrication allow us now to construct a skin-muscle type system combining interfacial liquid repellence atop a mechanically functional structure. Specifically, we design surfaces comprising bioinspired, mushroom-like repelling heads and spring-like flexible supports, which are realized by three-dimensional direct laser lithography. The flexible supports elevate liquid repellency by resisting droplet impalement and reducing contact time. This, previously unknown, use of spring-like flexible supports to enhance liquid repellency provides an excellent level of control over droplet manipulation. Moreover, this extends repellent microstructure research from statics to dynamics and is envisioned to yield functionalities and possibilities by linking functional surfaces and mechanical metamaterials.

Droplet Bouncing: Fundamentals, Regulations, and Applications

“…Numerical investigations of the droplet impact on flexible surfaces were further carried out by Xiong et al to find the ranges of parameters for the impact contact time reduction and rebounding momentum enhancement. [ 75 ] Recently, with the development of micro/nanofabrication techniques, Hu et al designed microscale spring‐like flexible supports (diameters are less than 100 µm) by 3D direct laser lithography, [ 76 ] and the impalement probability of the impact by millimeter‐sized droplet is also largely reduced on the non‐wetting surface with the microscale flexibility.…”

Biomimetic Water-Repelling Surfaces with Robustly Flexible Structures

“…Specifically, the impalement resistance was shown to reach an improvement of ~ 80% by triggering the structural tilting movements, around ~ 5 times higher than previous studies. 26 Such tilting movements were also applied to repelling obliquely impacting water droplets. We believe this study to be the very first demonstration of flexible interfacial structures to robustly endure tribological friction as well as to promote water repellency, approaching real-world applications of water-repelling.…”

“…Differing from a needle-like flexible microstructure utilizing bending movements at droplet impact, 27,28 the mushroom-like microstructure has substituted its pillar-like rigid support with a spring-like flexible one. 26 Such a microstructure is, however, criticized for weak mechanical robustness (tribological fiction under ~ 0.04 N mm −1 ) and limited repellency enhancement (~ 15%). 26,29 Here, we report a water-repelling biomimetic surface structured with singly re-entrant mushroom-like basic units through three-dimensional projection micro stereolithography, each unit comprising a mesoscale head and a microscale spring set.…”

“…26 Such a microstructure is, however, criticized for weak mechanical robustness (tribological fiction under ~ 0.04 N mm −1 ) and limited repellency enhancement (~ 15%). 26,29 Here, we report a water-repelling biomimetic surface structured with singly re-entrant mushroom-like basic units through three-dimensional projection micro stereolithography, each unit comprising a mesoscale head and a microscale spring set. Such a surface exhibits high recovery capability in response to ubiquitous normal and shear compression, even to achieve strong mechanical robustness against tribological friction under ~ 0.44 N mm −1 .…”

How Can Interfacial Phenomena in Nature Inspire Smaller Robots

“…[ 58 ] Furthermore, in the “Salvinia effect,” a combination of eggbeater‐shaped flexible microstructures and hydrophilic tips increase pinning of the water–air interface and the stability of an air film entrapped on the salvinia surface. [ 59 ] This emphasizes the need to consider more intricate designs of surface structures, [ 60 ] flexural deformations in the interaction of soft or compliant surfaces with liquids [ 61 ] and the potential of wettability patterns in order to pin contact lines in specific places. [ 62 ]…”