Bioinspired Strategies for Corrosion Protection and Antifouling Coatings

Steel is a ubiquitous material in load-bearing structures and vehicles such as automobile and ship components worldwide, but its susceptibility to corrosion poses significant challenges. Metal loss in offshore conditions is found to be more than that in onshore conditions. The sea has many contaminants such as microorganisms, bacteria, and parasites such as barnacles. They colonize surfaces, form biofilms, and produce by-products such as organic acids, hydrogen sulfide, and slime. Additionally, the turbulent boundary layer created by barnacles and slime along the mobile vessel body increases drag, prevents ship from clean cutting of water and lead to increased fuel consumption. Therefore, offshore surfaces require both antifouling and anticorrosion coatings for better performance and improved service life. Conventionally, organic coatings broadly called paints are being used for protection against corrosion which act as a barrier between the metal substrate and the corrosion media. Among various classes of coatings, organic-inorganic hybrid sol-gel coatings are very effective, economical, environmentally friendly, flexible, and versatile to obtain corrosion protection. The addition of corrosion inhibitors into the sol-gel matrix to further enhance resistance is a widely researched topic. Incorporating corrosion inhibitors directly into coating formulations can potentially trigger undesirable and premature consumption. Thus, encapsulation of the corrosion inhibitor becomes a necessary approach to address the issue. Further, taking cues from nature and the self-healing ability of the human body, incorporating encapsulated corrosion inhibitor into the coatings can provide a self-healing effect, enhancing the corrosion protection and prolonging the life span of metal. Moreover, low surface free energy thin films derived from sol-gel organic and inorganic hybrids render the coated surfaces hydrophobic, preventing contaminants and bacterial adhesion thereby serving as an effective antifouling coatings for many practical applications. Since the traditional method of preparing antifouling coating is not appreciated due to its cytotoxicity, researchers have now completely focused on nature-inspired antifouling coatings. Organic-inorganic nanocomposite coatings help in implementing ideas derived from nature using the concepts of superhydrophobic coating and liquid-infused omniphobic slippery coating for imparting antifouling functionality. For instance, the lotus leaf-inspired superhydrophobic surface with micro/nanoscale roughness effectively repels microorganisms. Alternatively, eco-friendly biocides can be integrated into coatings for direct killing of attached microorganisms. Hence, a sol-gel coating protects the coated surface not only from corrosion, but also from fouling due to the surrounding medium. This chapter will cover recent advancements in biomimetic antifouling and anticorrosion coatings with a special emphasis on sol-gel technique.