Hybrid copper(II)acrylate/silazane thin coatings with hydrophobic and germicidal properties

Thousands of deaths related to infectious diseases caused by bacteria are reported yearly within the EU. The spread of such microorganisms is often associated with the personal contact with infected surfaces, which can be avoided by the deposition of coatings with self-cleaning or germicidal properties. Therefore, the hydrophobic character of the oligosilazane Durazane 1800 was combined with the germicidal properties of copper(II)acrylate in a hybrid organic/inorganic coating. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) of the hybrid coatings on AISI 304 steel confirmed the homogeneous distribution of Cu and Si in a molar ratio of 0.3 (Cu:Si) within a dense and well-adherent 4 μm thick layer after annealing at 135 °C for 24 h in air. The good adhesion (GT 2) and scratch tolerance (20 N) of the coatings were respectively attributed to the formation of Si-O-Fe bonds between the silazane and the substrate and to the polymeric character of the hybrid system. The exposure of -CH3 and -CH=CH2 hydrophobic groups of the silazane to the surface of the coating system was responsible for its hydrophobic character, resulting in a contact angle of 99.8° with water. Its germicidal potential was comparable to pure copper as confirmed by live/dead assay tests, where the number of living bacteria was reduced over 99%, which can be correlated to the release of Cu2+ ions from the coating. A direct cell count technique was used to measure the influence on bacterial colonization. Furthermore, the material exhibited an enhanced chemical resistance during exposure to isopropanol and concentrated H2O2 (30 wt%) for 24 h, leading only to minimal signs of degradation.