Self-regenerative superhydrophobic metallic coatings with enhanced durability

Abstract

Lotus-inspired superhydrophobic surfaces are highly sought owing to exquisite properties such as de-wetting, self-cleaning, anti-corrosion, anti-fouling. However, their use is limited due to low durability, high processing cost, and scalability issues. In the present work, we used low cost and simple flame spraying for developing self-regenerative superhydrophobic metallic coatings with high durability and corrosion resistance. The aluminum coatings were developed on low-carbon steel at optimized parameters, followed by annealing at different temperatures. The developed coating showed hierarchical structure with nanoscale features superimposed on microscale lamellae. The nano-sponge like morphology obtained through flame spraying after annealing transformed into nano-spheroid with reduced microscale porosity. The fabricated aluminum coatings inherently exhibited superhydrophilicity, which transformed to superhydrophobicity after silanization. The coatings exhibited advancing angles >150° and receding angles >148° with a 5° sliding angle. The change in morphology with annealing showed a significant influence on wettability, adhesion, and electrochemical corrosion. The contact angles decreased slightly with annealing temperature while still in the superhydrophobic regime. The adhesion of the coatings with the water droplet increased from ~2 μN to 7.3 μN with the increase in annealing temperatures while still being less than that of the lotus leaf (18 μN). The electrochemical corrosion resistance of the coatings showed significant improvement after annealing, which is related to the change in microporosity and formation of stable oxides as verified by x-ray photoelectron spectroscopy (XPS). The current density decreased from 0.48 μA/cm2 to 0.06 μA/cm2 due to stable passive layer formation. The coatings showed increased durability against abrasion, and impacting droplets due to improved inter-lamellar cohesion and increased adhesion with the substrate. The present work provide a low cost and facile solution for the development of superhydrophobic coatings for various applications.