Long term antifouling performance of superhydrophobic surfaces in seawater environment: Effect of substrate material, hierarchical surface feature and surface chemistry

A comprehensive review on anticorrosive/antifouling superhydrophobic coatings: Fabrication, assessment, applications, challenges and future perspectives

Superhydrophobicity (SHP) is an incredible phenomenon of extreme water repellency of surfaces ubiquitous in nature (E.g. lotus leaves, butterfly wings, taro leaves, mosquito eyes, water-strider legs, etc). Historically, surface exhibiting water contact angle (WCA) > 150° and contact angle hysteresis <10° is considered as SHP. The SHP surfaces garnered considerable attention in recent years due to their applications in anti-corrosion, anti-fouling, self-cleaning, oil-water separation, viscous drag reduction, anti-icing, etc. As corrosion and marine biofouling are global problems, there has been focused efforts in combating these issues using innovative environmentally friendly coatings designs taking cues from natural SHP surfaces. Over the last two decades, though significant progress has been made on the fabrication of various SHP surfaces, the practical adaptation of these surfaces for various applications is hampered, mainly because of the high cost, non-scalability, lack of simplicity, non-adaptability for a wide range of substrates, poor mechanical robustness and chemical inertness. Despite the extensive research, the exact mechanism of corrosion/anti-fouling of such coatings also remains elusive. The current focus of research in recent years has been on the development of facile, eco-friendly, cost-effective, mechanically robust chemically inert, and scalable methods to prepare durable SHP coating on a variety of surfaces. Although there are some general reviews on SHP surfaces, there is no comprehensive review focusing on SHP on metallic and alloy surfaces with corrosion-resistant and antifouling properties. This review is aimed at filling this gap. This review provides a pedagogical description with the necessary background, key concepts, genesis, classical models of superhydrophobicity, rational design of SHP, coatings characterization, testing approaches, mechanisms, and novel fabrication approaches currently being explored for anticorrosion and antifouling, both from a fundamental and practical perspective. The review also provides a summary of important experimental studies with key findings, and detailed descriptions of the evaluation of surface morphologies, chemical properties, mechanical, chemical, corrosion, and antifouling properties. The recent developments in the fabrication of SHP -Cr-Mo steel, Ti, and Al are presented, along with the latest understanding of the mechanism of anticorrosion and antifouling properties of the coating also discussed. In addition, different promising applications of SHP surfaces in diverse disciplines are discussed. The last part of the review highlights the challenges and future directions. The review is an ideal material for researchers practicing in the field of coatings and also serves as an excellent reference for freshers who intend to begin research on this topic.

Durable Superhydrophobic Coatings on Tungsten Surface by Nanosecond Laser Ablation and Fluorooxysilane Modification

Tungsten is an attractive material for a variety of applications, from constructions in high-temperature vacuum furnaces to nontoxic shields for nuclear medicine, because of its distinctive properties, such as high thermal conductivity, high melting point, high hardness and high density. At the same time, the areas of the applicability of tungsten, to a large extent, are affected by the formation of surface oxides, which not only strongly reduce the mechanical properties, but are also prone to easily interacting with water. To alleviate this shortcoming, a series of superhydrophobic coatings for the tungsten surface was elaborated using the method of nanosecond laser treatment followed by chemical vapor deposition of hydrophobic fluorooxysilane molecules. It is shown that the durability of the fabricated coatings significantly depends on surface morphology and composition, which in turn can be effectively controlled by adjusting the parameters of the laser treatment. The coating prepared with optimized parameters had a contact angle of 172.1 ± 0.5° and roll-off angle of 1.5 ± 0.4°, and preserved their high superhydrophobic properties after being subjected to oscillated sand abrasion for 10 h, continuous contact with water droplets for more than 50 h, and to several cycles of the falling sand test.