Modification of silicon-polyurethane-based sol–gel coatings through diverse plasma technologies: investigation of impact on surface properties

Abstract

Sol–gel coatings have many benefits in industrial applications, thanks to their simple low-temperature preparation processes and easy-to-alter dimensions. However, they often require curing through heating at elevated temperatures or UV radiation, which can increase manufacturing complexity and energy consumption. To overcome this challenge, we propose an alternative method for curing sol–gel coatings quickly and easily using various atmospheric pressure cold or hot plasma technologies, such as plasma jet, diffuse coplanar surface barrier discharge, and gliding arc technology. Our research involves preparing light-transparent sol–gel coatings on stainless-steel substrates via the spin-coating method, using a unique combination of commercially available organic precursors that could be used as water and corrosion-resistant protective paints. We analyse the efficiency of plasma curing by examining the morphological changes, water adhesion, and chemical changes induced by plasma treatment using a scanning electron microscope, contact angle measurement, X-ray photoelectron spectroscopy, nanoindentation, scratch testing, and Fourier transform infrared spectroscopy. According to these measurements, the choice of plasma technology can affect the modification of surface chemistry and water adhesion. The DCSBD plasma changes the surface the most; the layer becomes hydrophilic, not hydrophobic, as with the other curing methods. In addition, post-curing of the layers treated with agliding arc, plasma jet or hotplate can be seen over time. Post-curing is described by the reaction of Si–O–C to Si–O–Si. This reaction path can be easily measured with XPS and FTIR. This post-curing also affects the adhesion of the coating to the substrate. The adhesion improves for all samples, except for the DCSBD-treated sample. However, the coating hardness was increased by the plasma treatment in all samples.