Stability Mechanism of Laser-induced Fluorinated Super-hydrophobic Coating in Alkaline Solution

Haoyang Li,Zhen Yang,Yanling Tian

doi:10.1007/s42235-021-00111-x

Abstract

Great attention has been focused on super-hydrophobic surfaces due to their fantastic applications. Fluoride chemicals are widely used to fabricate super-hydrophobic surfaces due to their convenience, simplicity, and high efficiency. Previous research has made extensively efforts on corrosion resistance of fluorinated super-hydrophobic surfaces in corrosive media. Nevertheless, rare papers focused on the underlying reasons of anticorrosion property and stability mechanism on the fluorinated super-hydrophobic coatings in alkaline solution. Therefore, this work aims to reveal these mechanisms of fluorinated super-hydrophobic copper samples in strong alkaline solution (pH 13). Through the characterization of surface wettability and surface morphology, the laser-induced super-hydrophobic surface retained excellent stability after soaking in alkaline solution for 4 h. Through measurement of chemical compositions, the anticorrosion mechanism and stability mechanism of the fluorinated super-hydrophobic surface were proposed. Importantly, the hydroxyl ion (OH−) can further promote the hydrolysis reaction to improve the density and bonding strength of the fluoride molecules. Finally, the electrochemical experiments (PDP and EIS tests) were conducted to validate the rationality of our proposed conclusions.

Highlights

Functional surfaces with super-hydrophobic property have aroused great attention from academic to industrial because of their broad ranges of applications, including self-cleaning [1], anti-icing [2], oil-separation [3], anti-bacteria [4], fluid drag reduction [5], and even energy storage devices [6]
Surface wettability of the pristine copper, super-hydrophobic copper and their corresponding alkaline-etched samples was investigated by measuring Water Contact Angle (WCA) and Rolling Angle (RA)
After soaking in alkaline solution for 4 h, the WCA of Alkaline-Etched Pristine (AEP) copper experienced a sharp decrease, and the value was only 49.2 ± 1.0°. This phenomenon implied that the strong alkaline solution had dramatically damaged the flat copper surface to generate rough micro/nano-structures, causing a huge change in surface wettability

Summary

Introduction

Functional surfaces with super-hydrophobic property have aroused great attention from academic to industrial because of their broad ranges of applications, including self-cleaning [1], anti-icing [2], oil-separation [3], anti-bacteria [4], fluid drag reduction [5], and even energy storage devices [6]. It has been demonstrated that the fluorinated super-hydrophobic surfaces have superior corrosion resistance capability because of their ability to minimize the contact area between substrates and liquid media when being immersed underwater [25]. The stability and durability of fluorinated super-hydrophobic coatings in corrosive liquids (acid, salt, and alkaline solution) have been explored to determine their possible applications in specific working environment. The fluorinated nickel coating has been successfully fabricated on stainless steel in Liang’s research group, and the corresponding results proved that such super-hydrophobic nickel film possessed satisfied stability and durability after being immersed into strong acid solution (pH 2) and alkaline solution (pH 13) [27]. The protective mechanism and failure reason were not revealed in these two studies from the perspective of physical changes and chemical reactions when the fluorinated super-hydrophobic surfaces were soaked into corrosive alkaline media. It is urgent to systematically explore the underlying reasons to elucidate the interaction mechanisms between the fluorinated superhydrophobic coatings and corrosive media

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Conclusion