Colloids and Surfaces A: Physicochemical and Engineering Aspects
Facile fabrication of biomimetic liquid-infused slippery surface on carbon steel and its self-cleaning, anti-corrosion, anti-frosting and tribological properties
Graphical abstract
A facile and commercial nanosecond laser treatment method was developed to fabricate slippery surface on carbon steel materials.
Introduction
In the recent years, fabrication of anti-wetting surfaces has garnered widespread attention, which is promising to solve many traditional industrial problems, such as corrosion damage, ice accretion, water-harvesting, oil/water separation, biofouling, and so on [[1], [2], [3], [4]]. In nature, lotus leaf is well-known for its self-cleaning behavior and this phenomenon has been demonstrated by researchers to be dependent on its unique hierarchical micro/nano structure and epicuticular wax coating [5]. Based on this principle, superhydrophobic surface has been successfully created on numerous materials through a variety of approaches, aiming to improve the working performance of traditional materials in harsh conditions [[6], [7], [8], [9]]. Due to the great water repellence of superhydrophobic surface, water droplets are supposed to be suspended on its hierarchical structure in Cassie-Baxter state with air layer trapped underneath [10]. However, superhydrophobic surface has been reported to be susceptible to dynamic effects and mechanical damage due to the instability of trapped air layer and the limited micro/nano topographical structure [[11], [12], [13]]. Furthermore, water condensation could also take place in its porous structure and hence destroy the Cassie-Baxter state [13]. Thus, it is urgent to develop a new type of anti-wetting surface with improved working performance to substitute superhydrophobic surface.
Liquid-infused slippery surface, which was first proposed by Aizenberg, has been treated as promising repellent surface to replace superhydrophobic surface in practical application [14]. The fabrication of slippery surface is inspired by nepenthes pitcher plant, which is characterize by rough porous top surface and dynamic oil layer. The infused lubricant oil could spread over the entire surface and fill in the porous micro/nano structure, generating a continuous, homogeneous, smooth and defect-free oil film [15]. As slippery surface relies on oil layer rather than air layer to repel liquids, it could withstand certain dynamic effects [14]. Endowing functional surface with smart self-healing property has also aroused researchers’ attention to improve its working performance, like autonomous self-healing coating consisting of supramolecular polymers and nanocontainers or non-autonomous self-healing coating which needs external stimulation [16,17]. Owing to the certain mobility of lubricant oil, slippery surface has been reported to have certain intrinsic self-healing property, which hence enhances its mechanical durability and service life [[18], [19], [20]]. Furthermore, slippery surface has also been reported to be able to hinder water condensation and nucleation by allowing water droplets to slide off, decreasing the possibility of icing and frosting [21,22]. The anti-wetting oil film could also separate substrate from corrosive medium, which hence offers superior corrosion protection to underneath steel.
In order to achieve great repellence to various liquids, the oil selected for constructing slippery surface should be immiscible to most liquids. Silicone oil and perfluorinated oil, which have a low surface tension and viscosity, have been reported by many Refs. [[23], [24], [25], [26]] to be immiscible to various nonpolar and polar liquids. Furthermore, the porous top surface structure is also necessary to be chemically modified to strongly hold the oil layer. As a result, a stable anti-wetting lubricant oil film could be formed due to the capillary effect and Van der Waals force. Zhang et al [27] fabricated slippery surface on Mg alloy by first producing a double-layered structure through hydrothermal process, and then chemically modified the porous structure with PFTS (1H,1H,2H,2H-perfluorooctyltriethoxysilane) before infusing perfluoropolyethe (PFPE) oil. To fabricate slippery surface on mild steel, Xiang et al [28] first created superhydrophobic coating by electroplating and fluoroalkylsilane modification, and then infused lubricant oil (Krytox 100) on as-prepared superhydrophobic coating. Song et al [24] constructed slippery surface by infusing silicone oil in the porous anodic aluminum oxide. Carbon steel materials have been extensively used in industry field, but its further widespread application is hindered by less corrosion resistance and anti-frosting performance. Thus, it is urgent to develop a facile and commercial way to create effective slippery surface with excellent corrosion resistance and frosting-resistant properties on carbon steel to expand its further industrial applications. Considering the future industrial working environment, the prepared slippery surface should also exhibit desirable self-cleaning and tribological performances, which could improve its robustness and stability and hence makes it more competitive for working in harsh working conditions. Up to now, various techniques have been reported to fabricate slippery surface, including chemical etching, ion anodization, hydrothermal, lithography and spray coating, etc. [[2], [3], [4], [5], [6], [7], [8]]. Compared with other techniques, nanosecond laser treatment is more facile, effective and commercial, and it also shows superior localization control capability. At present, laser treatment combined with long-time exposure in air has been reported to be effective in endowing steel surface with hydrophobic or even superhydrophobic property [9]. However, such process is time-consuming and low efficient, making it unattractive for future large-scale applications. The other approach is to combine laser texturing technique with chemical modification like FAS-17 modification, which could significantly reduce the processing time and hence made it competitive for future industrial application.
In this paper, a facile and commercial nanosecond laser treatment was developed to create slippery surface, and the schematic diagram could be seen in Fig.1. First, porous and multilevel micro/nano structure was fabricated on carbon steel. Then, the laser-processed steel surface was subject to fluorination process to decrease the surface energy. Finally, PFPE oil was selected to be infused on as-prepared fluorinated steel specimen to form a smooth and uniform lubricant layer, and the low-surface-tension and volatilization of PFPE oil was expected to endow slippery surface with desirable liquid repellence and stability. The results showed that the fabricated slippery surface displayed desirable hydrophobic and slippery properties. Owing to the anti-wetting, isolative and self-healing effects of lubricant layer, the prepared slippery surface also exhibited great self-cleaning, anti-corrosion and anti-frosting performances. Furthermore, because of the lubricating effect of lubricant layer, the fabricated slippery surface also showed superior tribological property. Thus, the prepared slippery surface is promising to enlarge the industrial application of conventional carbon steel materials.
Section snippets
Materials
Commercial S45C carbon steel plate with the composition of C (0.45 wt. %), Mn (0.60 wt. %), Si (0.24 wt. %), S (0.018 wt. %), P (0.009 wt.%) and Fe (balance) was employed as the base steel material. 1H,1H,2H,2H-perfluorodecyltriethoxysilane (FAS-17, purity = 97%) was provided by Sigma-Aldrich and used for chemical modification, and Dupont Krytox 105 perfluoropolyether (PFPE) oil was used as lubricant. All reagents used in this experiment were AR grade. All reagents used in this experiment were
Surface morphology and wettability
Laser irradiation treatment was conducted on carbon steel to produce porous hierarchical surface morphology. Fig.2a and b showed the corresponding SEM images of steel sample surface after laser treatment. It could be seen in Fig.2a that the microstructure of steel surface had become quite porous and rough, demonstrating the effectiveness of laser irradiation in processing steel materials with desirable porous structure. From the high-magnification image of laser irradiated area, as illustrated
Conclusions
In this paper, a facile and commercial nanosecond laser treatment method was developed to fabricate slippery surface on carbon steel, and its wetting, self-cleaning, anti-corrosion, anti-frosting and tribological properties were analyzed systematically. The results showed that laser treatment was effective in producing desirable porous and multilevel micro/nano structure on base steel. After FAS-17 modification and lubricant oil infusion, slippery surface with a low contact angle hysteresis was
Acknowledgement
The first author sincerely thanks the financial support from China Scholarship Council (CSC, No. 201806280152).
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