Atmospheric pressure plasma jet polymerization of silicon-based coatings for the protection of glass from atmospheric alteration

Alternative methods to sol-gel coatings have gained considerable research attention in recent decades. Among these, plasma-polymerised coatings have proven to be effective in enhancing homogeneity, thinness and adhesion to treated surfaces. Due to these advantages, plasma technologies have also emerged as promising tools in the conservation field, particularly for treating fragile and specialised materials like glass. This study investigates the application of an atmospheric pressure plasma jet for depositing two silica-based coating on glass using two distinct precursors - the inorganic silane TEOS and the organo-silane HMDSO. In this context, plasma polymerisation refers to the plasma-induced fragmentation and recombination of precursor molecules, resulting in the formation of cross-linked inorganic or hybrid films. The relationship between plasma deposition parameters and coating properties was analysed to achieve precise control over film thickness and morphology. The barrier properties and the stability of the coatings were further evaluated under artificial ageing conditions, involving 70 ◦C and cycling relative humidity between 10 % and 90 %. Results revealed that while inorganic plasmapolymerised films provide some degree of protection by preventing precipitate formation on glass surface, their performance is limited by densification process that occurs during ageing. In contrast, hybrid plasmapolymerised coatings exhibited superior protective properties, attributed to the incorporation of organic groups that enhanced barrier performance and effectively prevented calcium leaching.