Substrate-Independent, Fast, and Reversible Switching between Underwater Superaerophobicity and Aerophilicity on the Femtosecond Laser-Induced Superhydrophobic Surfaces for Selectively Repelling or Capturing Bubbles in Water.

Jiale Yong,Feng Chen,Subhash C Singh,Chunlei Guo,Zhibing Zhan

doi:10.1021/acsami.8b21465

Abstract

In this paper, the reversible switching between underwater (super-) aerophilicity and superaerophobicity was achieved on various femtosecond (fs) laser-induced superhydrophobic surfaces. A range of materials including Al, stainless steel, Cu, Ni, Si, poly(tetrafluoroethylene), and polydimethylsiloxane were first transformed to superhydrophobic after the formation of surface microstructures through fs laser treatment. These surfaces showed (super-) aerophilicity when immersed in water. In contrast, if the surface was prewetted with ethanol and then dipped into water, the surfaces showed superaerophobicity in water. The underwater aerophilicity of the superhydrophobic substrates could easily recover by drying. The switching between the underwater aerophilicity and superaerophobicity can be fast repeated many cycles and is substrate-independent in stark contrast to common wettability-switchable surfaces based on stimuli-responsive chemistry. Therefore, the as-prepared superhydrophobic surfaces can capture or repel air bubbles in water by selectively switching between underwater superaerophobicity and aerophilicity. Finally, we demonstrated that the underwater bubbles could pass through an underwater aerophilic porous sheet but were intercepted by an underwater superaerophobic porous sheet. The selective passage of the underwater bubbles was achieved by the reversible switching between the underwater aerophilicity and superaerophobicity. We believe that this substrate-independent and fast method of switching air wettability has important applications in controlling air behavior in water.

Highlights

After laser processing and subsequent fluoroalkylsilane modification, the resultant Al surface possessed ultralow adhesive superhydrophobicity. When such surface was immersed in water, the surface showed superaerophilicity with the bubble CA (BCA) of 6 ± 2.4°
The as-prepared superhydrophobic surface showed underwater superaerophobicity with the BCA of 154.9 ± 1.4° if it was prewetted by ethanol and dipped into water
The switchable bubble wettability was achieved on other laser-induce superhydrophobic surfaces

Summary

INTRODUCTION

Smart surfaces with switchable wettability have attracted broad interest because they can selectively exhibit different and even inversed superwetting states.[1−4] Such materials can reversibly switch their static and dynamic wettabilities by responding to different external stimulations, such as temperature,[5−10] light,[11−18] pH,− electrical potential,[24−26] and magnetic field.[27−29] The wettability-switchable surfaces are generally prepared by modifying rough microstructures with stimuli-responsive molecules or directly generating surface microstructures on stimuli-responsive materials.[1−3] For example, Sun et al grafted the thermalresponsive poly(N-isopropylacrylamide) molecules onto a micro/nanostructured silicon substrate.[7]. Our group achieved switchable underwater superoleophobicity−superoleophilicity on the laserstructured TiO2 surface through alternate UV irradiation and dark storage.[12] Jiao et al created multiscale TiO2 square micropillars on a titanium surface by femtosecond (fs) laser treatment.[32] The original sample showed superaerophobicity in water, whereas it became underwater superaerophilic after heating in a dark environment for 0.5 h. After irradiated by UV light for 1 h, the sample could recover its underwater superaerophobicity Such switchable bubble wettability is ascribed to the chemical conversion between Ti−OH and Ti−O. The reversible switching between underwater (super-) aerophilicity and superaerophobicity was achieved on the fs laser-induced superhydrophobic substrates. After the formation of surface microstructures, different kinds of substrates were transformed to ultralow adhesive superhydrophobicity These surfaces originally showed (super-) aerophilicity in water. The drying treatment was performed by blowing the samples with a high-pressure air duster (CompuCleaner 2.0, EasyGo)

RESULTS AND DISCUSSION

EXPERIMENTAL SECTION

CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES