Pneumatic smart surfaces with rapidly switchable dominant and latent superhydrophobicity

Abstract

Smart surfaces that possess switchable wettability are highly desired for a broad range of applications. However, the realization of novel approaches enabling complete alteration of surface properties independent of chemical environment and special materials is still challenging. Herein, inspired by the air sacs of insects, we fabricate a pneumatic smart surface that possesses dual-property wetting behavior and permits fast switching between states. The pneumatic surface is based on an embedded micro-air-sac network composed of an elastomer that was fabricated via a stretching-assisted mismatch-bonding process. By simply pumping the air sacs, the surface could undergo rapid and large-amplitude topography deformation, thereby exposing one surface and hiding the other, and the dominant surface and the latent surface could be switched reversibly. As a typical example, we demonstrate a smart surface with contrasting 'petal' and 'lotus' effects that enables the on-demand capture and release of water droplets. Our pneumatic strategy demonstrates a currently underexploited platform for the development of switchable smart surfaces. NPG Asia Materials (2018) 10, e470; doi:10.1038/am.2017.218; published online 16 February 2018 INTRODUCTIONWith the aid of superwettable biointerfaces, 1 natural creatures have developed a myriad of survival skills, for instance, self-cleaning, 2 aquatic walking 3 and fog collection, 4 that inspire the development of artificial surfaces with superb wetting properties that are similar or superior to those observed in nature. [5][6][7] For example, derived from the lotus effect, 8 superhydrophobic surfaces with low water adhesion can promote rapid droplet departure, enabling a broad range of applications, such as corrosion resistance, 9 drag reduction 10 and anti-icing. 11 In contrast, the adhesive superhydrophobic surfaces recently observed on rose petals 12 can facilitate droplet pinning, and they exhibit great potential for droplet manipulation 13 and nanopatterning. 14 As each wetting mode features different properties and functions, solid surfaces with a fixed wetting behavior are significantly limited in some cuttingedge applications, the most obvious example of which is the development of intelligent devices, [15][16][17][18][19][20] in which there is a need to control the surface wettability dynamically and reversibly. [21][22][23] Hence, smart surfaces that possess multiple dewetting properties and permit flexible switching between them, similar to chameleons that expertly change camouflage colors on demand, are highly desired.It has been well established that surface wettability is governed by chemical composition and geometric structure. To acquire tunable surface wettability, research efforts have been substantially devoted to attaining exquisite control over surface chemistry. By building hierarchical micro-/ nanostructures with stimuli-responsive materials, researchers have successfully prepared various smart surfaces with switchable wettability. 6,[22][23][24][25][26]

Three-Dimensional Multifunctional Magnetically Responsive Liquid Manipulator Fabricated by Femtosecond Laser Writing and Soft Transfer

“…Organisms in nature use their unique surface structures to directionally and spontaneously transport droplets. − In practical applications, droplets manipulation is crucial for bioassays , and chemical microreactions. , Artificial passive droplet manipulation surfaces have been already prepared for energy-free droplets manipulation. − However, they are usually inefficient and irreversible. In contrast, intelligent topography surfaces can dynamically and reversibly change the surface topography in response to external stimuli, such as mechanical forces, − pneumatic stimuli, wet stimuli, , and magnetic fields, − so as to realize the horizontal − or vertical − , droplets manipulation. Among them, the magnetically responsive intelligent topography (MIT) surfaces have gained great expectations for active droplet manipulation due to their incomparable advantages including biocompatibility, instantaneous response, and battery-free remote control. , …”

Active Surface with Dynamic Microstructures and Hierarchical Gradient Enabled by in situ Pneumatic Control

“…The pneumatic surface consisted of two elastomer layers, including a structured substrate with microchannels and a cover slice. Both of the two layers were made from polydimethylsiloxane (PDMS) elastomer (Sylgard 184 silicone, Dow Corning, MA, USA) which is widely used in soft-actuated systems and lab-on-a-chip (LoC) devices [21][22][23], due to their high flexibility and ease of processing. The pattern of microchannels was first defined by photolithography.…”

Bioinspired Surfaces With Switchable Wettability

“…This smart surface shows potential in droplet manipulations by movable joints. Similarly, this group developed pneumatic surfaces by embedding micro-air-sac network in an elastomer ( Figure 1k ; Wang et al, 2018a ). The surface exposes one surface and hiding the other by deflation and inflation.…”

“…(k) Pneumatic response. Reproduced under the terms of the CC-BY Creative Commons Attribution 4.0 International License ( http://creativecommons.org/licenses/by/4.0/ ) (Wang et al, 2018a ). Copyright 2018, the authors, published by Springer Nature.…”