The effect of superhydrophobic wetting state on corrosion protection--the AKD example

Evaluation of a Hydrophobic Coating Agent Based on Cellulose Nanofiber and Alkyl Ketone Dimer

In this study, we report on the development and testing of hydrophobic coatings using cellulose fibers. The developed hydrophobic coating agent secured hydrophobic performance over 120°. In addition, a pencil hardness test, rapid chloride ion penetration test, and carbonation test were conducted, and it was confirmed that concrete durability could be improved. We believe that this study will promote the research and development of hydrophobic coatings in the future.

Effects of liquid surface tension on gas capillaries and capillary forces at superamphiphobic surfaces

The formation of a bridging gas capillary between superhydrophobic surfaces in water gives rise to strongly attractive interactions ranging up to several micrometers on separation. However, most liquids used in materials research are oil-based or contain surfactants. Superamphiphobic surfaces repel both water and low-surface-tension liquids. To control the interactions between a superamphiphobic surface and a particle, it needs to be resolved whether and how gas capillaries form in non-polar and low-surface-tension liquids. Such insight will aid advanced functional materials development. Here, we combine laser scanning confocal imaging and colloidal probe atomic force microscopy to elucidate the interaction between a superamphiphobic surface and a hydrophobic microparticle in three liquids with different surface tensions: water (73 mN m^-1), ethylene glycol (48 mN m^-1) and hexadecane (27 mN m^-1). We show that bridging gas capillaries are formed in all three liquids. Force-distance curves between the superamphiphobic surface and the particle reveal strong attractive interactions, where the range and magnitude decrease with liquid surface tension. Comparison of free energy calculations based on the capillary menisci shapes and the force measurements suggest that under our dynamic measurements the gas pressure in the capillary is slightly below ambient.

Recent Progresses of Superhydrophobic Coatings in Different Application Fields: An Overview

With the development of material engineering and coating industries, superhydrophobic coatings with exceptional water repellence have increasingly come into researchers’ horizons. The superhydrophobic coatings with corrosion resistance, self-cleaning, anti-fogging, drag-reduction, anti-icing properties, etc., meet the featured requirements from different application fields. In addition, endowing superhydrophobic coatings with essential performance conformities, such as transparency, UV resistance, anti-reflection, water-penetration resistance, thermal insulation, flame retardancy, etc. plays a remarkable role in broadening their application scope. Various superhydrophobic coatings were fabricated by diverse technologies resulting from the fundamental demands of different fields. Most past reviews, however, provided only limited information, and lacked detailed classification and presentation on the application of superhydrophobic coatings in different sectors. In the current review, we will highlight the recent progresses on superhydrophobic coatings in automobile, marine, aircraft, solar energy and architecture-buildings fields, and discuss the requirement of prominent functionalities and performance conformities in these vital fields. Poor durability of superhydrophobic coating remains a practical challenge that needs to be addressed through real-world application. This review serves as a good reference source and provides insight into the design and optimization of superhydrophobic coatings for different applications.

A facile, fast, and low-cost method for fabrication of micro/nano-textured superhydrophobic surfaces

HYPOTHESIS

Alkyl ketene dimer (AKD) is frequently used in paper industry as an inexpensive sizing agent. The formation of a porous structure after curing the solidified AKD for an extra-long time (4-6 days) results in superhydrophobicity. In this study, a facile and low-cost method was utilized to turn the surface of AKD superhydrophobic in a very short period of time.

EXPERIMENTS

We fabricated superhydrophobic coatings by dipping glass and paper substrates in molten AKD and then treating them with ethanol after solidification. The samples were characterized by X-ray diffraction, Scanning electron microscopy, Fourier transform-infrared spectroscopy, X-ray photoelectron spectroscopy, Confocal laser scanning microscopy, and dynamic contact angle goniometry.

FINDINGS

The results show that briefly treating the coatings, obtained from isothermally heated AKD melt at 40 °C for 3 min, with ethanol leads to superhydrophobicity with advancing and receding contact angles of 158.7 ± 1.4° and 156.8 ± 0.9°, respectively. By increasing the melt temperature to 70 °C and its heating time to 6 h followed by ethanol treatment, the advancing and receding contact angles increased to 163.7 ± 1.3° and 162.6 ± 1.2°, respectively. This enhancement in superhydrophobicity is due to the formation of porous, entangled irregular micro/nano textures that create air cushions on the surface resulting in droplet state transition from Wenzel to Cassie.

Super-Amphiphobic Coating System Incorporating Functionalized Nano-Al2O3 in Polyvinylidene Fluoride (PVDF) with Enhanced Corrosion Resistance

Understanding the corrosion inhibition behavior of super-amphiphobic coating is important to ensure practicability in the real application. 2 layers system of super-amphiphobic coating was successfully developed using functionalized nano-Al2O3 incorporated in polyvinylidene fluoride (PVDF). This study investigates the effect of different amount of functionalizing agent on the coating’s repellency and its relationship toward the corrosion inhibition behavior. We found that a higher amount of fluoroalkylsilane (FAS) led to a decreased in repellency of both water and oil. Electrochemical impedance spectroscopy (EIS) analysis suggests that the synergetic effect between super-hydrophobicity, longer diffusion path, and barrier effect; enhanced the corrosion resistance. Although the coatings demonstrate similar behavior, the most superhydrophobic/amphiphobic coating C1 offers the highest corrosion protection.

Interaction of Surface Energy Components between Solid and Liquid on Wettability, and Its Application to Textile Anti-Wetting Finish

With various options of anti-wetting finish methods, this study intends to provide basic information that can be applied in selecting a relevant anti-wetting chemical to grant protection from spreading of liquids with different surface energy profiles. With such an aim, the anti-wetting effectiveness of fluorinated coating and silane coating was investigated for liquids having different surface energy components, water (WA), methylene iodide (MI) and formamide (FA). The wetting thermodynamics was experimentally investigated by analyzing dispersive and polar component surface energies of solids and liquids. The role of surface roughness in wettability was examined for fibrous nonwoven substrates that have varied surface roughness. The presence of roughness enhanced the anti-wetting performance of the anti-wetting treated surfaces. While the effectiveness of different anti-wetting treatments was varied depending on the liquid polarities, the distinction of different treatments was less apparent for the roughened fibrous surfaces than the film surfaces. This study provides experimental validation of wetting thermodynamics and the practical interpretation of anti-wetting finishing.

Stable Superhydrophobic Porous Coatings from Hybrid ABC Triblock Copolymers and Their Anticorrosive Performance

Superhydrophobic porous surfaces with ultralow water adhesion were successfully fabricated via micelle fusion-aggregation assembly of newly designed linear hybrid ABC triblock copolymers, where A, B, and C denote poly(dimethylsiloxane) (PDMS), polystyrene (PS), and poly(methacrylolsobutyl polyhedral oligomeric silsesquioxane) (PiBuPOSSMA), respectively. It was found that aggregation behavior in diluted solution and subsequent formation of nano-/microscale hierarchical surfaces in condensed state were affected by the molar mass of the triblock copolymers, which were evidenced by dynamic light scattering (DLS), SEM, and TEM studies. Increasing of PiBuPOSSMA content can significantly increase roughness of the resulting coatings, leading to an increase of apparent water contact angles from 145.7 ± 1° to 157.3 ± 1.1°. The optimized PDMS-PS-PiBuPOSSMA surface possesses unique nano/microscale hierarchical morphology, large apparent water contact angle (157.3 ± 1.1°), small roll-off angle (∼3°), low contact angle hysteresis (∼0.9°), long-term stability, and good chemical and thermal resistance. Moreover, it exhibits superior performance in preventing corrosive species such as ions and water in contact with the underlying metallic substrate (stainless steel) in 3.5 wt % NaCl aqueous solution with high inhibition efficiency and long-term preservability, which could be attributed to the synergistic effect of superhydrophobic surface and capillary action arising from the underlying porous structure.

Stability of plasma treated superhydrophobic surfaces under different ambient conditions

Plasma hydrophilizing of superhydrophobic substrates has become an important area of research, for example, superhydrophobic-(super)hydrophilic patterned surfaces have significant practical applications such as lab-on-chip systems, cell adhesion, and control of liquid transport. However, the stability of plasma-induced hydrophilicity is always considered as a key issue since the wettability tends to revert back to the untreated state (i.e. aging behavior). This paper focuses on the stability of plasma treated superhydrophobic surface under different ambient conditions (e.g. temperature and relative humidity). Water contact angle measurement and X-ray photoelectron spectroscopy are used to monitor the aging process. Results show that low temperature and low relative humidity are favorable to retard the aging process and that pre-storage at low temperature (-10°C) disables the treated surface to recover superhydrophobicity. When the aging is performed in water, a long-lasting hydropholicity is obtained. As the stability of plasma-induced hydrophilcity over a desired period of time is a very important issue, this work will contribute to the optimization of storage conditions of plasma treated superhydrophobic surfaces.

Synergistic Effect of Superhydrophobicity and Oxidized Layers on Corrosion Resistance of Aluminum Alloy Surface Textured by Nanosecond Laser Treatment

We report a new efficient method for fabricating a superhydrophobic oxidized surface of aluminum alloys with enhanced resistance to pitting corrosion in sodium chloride solutions. The developed coatings are considered very prospective materials for the automotive industry, shipbuilding, aviation, construction, and medicine. The method is based on nanosecond laser treatment of the surface followed by chemisorption of a hydrophobic agent to achieve the superhydrophobic state of the alloy surface. We have shown that the surface texturing used to fabricate multimodal roughness of the surface may be simultaneously used for modifying the physicochemical properties of the thick surface layer of the substrate itself. Electrochemical and wetting experiments demonstrated that the superhydrophobic state of the metal surface inhibits corrosion processes in chloride solutions for a few days. However, during long-term contact of a superhydrophobic coating with a solution, the wetted area of the coating is subjected to corrosion processes due to the formation of defects. In contrast, the combination of an oxide layer with good barrier properties and the superhydrophobic state of the coating provides remarkable corrosion resistance. The mechanisms for enhancing corrosion protective properties are discussed.