Fabrication of fluorine-free superhydrophobic coatings via sol-gel method and spray deposition

Superhydrophobic surfaces have marked increased attention in materials science due to their potential applications in self-cleaning, anti-corrosion, water-repellent, and antimicrobial technologies. Conventional coatings often rely on fluorinated compounds, which raise environmental and health concerns due to bioaccumulation. In this study, a sustainable method was developed to produce silicon-based superhydrophobic coatings via an one-step sol-gel process, applied through a spray-deposition technique using non-toxic solvents. The aim is to fabricate environmentally friendly coatings with high water contact angles on various substrates, offering a safer and effective alternative to fluorinated systems. In this study, a one-step sol-gel synthesis was used to prepare a low-viscosity organosilane solution using tetraethyl orthosilicate (TEOS) and hexadecyltrimethoxysilane (HDTMS) as the primary precursors, with ethanol and water as solvents. The solution was stirred at 60 °C to promote hydrolysis and ensure homogeneous mixing, resulting in a stable sol suitable for coating deposition. The coatings were deposited via a spray-deposition technique that is low cost and easily scalable for industrial use. A wide range of substrates—including paper, metals (Ti6Al4V, Al 1050 H14), plastic, cardboard, fabric, and brick—were coated to demonstrate the versatility of the method. Process parameters such as catalyst type and precursor ratios were optimized to ensure uniform deposition and achieve the highest contact angle with low contact angle hysteresis. Surface morphology was examined using scanning electron microscopy (SEM), while Fourier-transform infrared spectroscopy (FTIR) verified the chemical structure. Water contact angles were measured to confirm the superhydrophobic property of the coated surfaces. For Ti6Al4V, the contact angle reached approximately 164°, with contact angle hysteresis below 2°, as further confirmed by self-cleaning tests on the coated surface. Other substrates exhibited contact angles between 151° and 164°, along with effective self-cleaning performance.