Characterization of gas barrier silica coatings prepared from perhydropolysilazane films by vacuum ultraviolet irradiation

Abstract

Gas barrier silica coatings were prepared from perhydropolysilazane (PHPS) by vacuum ultraviolet (VUV) irradiation under several irradiation conditions to investigate the relationship between their water vapor transmission rate (WVTR) and the irradiation conditions. PET substrates were coated with PHPS using its xylene solution, and the coatings were irradiated with VUV light (172 nm). The oxygen concentrations and irradiation distances were varied. The sample irradiated under conditions of lower oxygen concentration (less than 5%) and shorter irradiation distance (2.6 mm) showed the lowest WVTR (0.721 g m² d⁻¹). The sample irradiated under conditions of higher oxygen concentration (19%) and longer irradiation distance (13.4 mm), on the other hand, showed the highest WVTR (2.738 g m² d⁻¹). These results suggest that VUV irradiation improves the gas barrier properties by Si–N bond cleavage rather than by oxidative reactions caused by O(¹D) and O₃.