Changes in surface properties of PI/WO2 сoatings after vacuum ultraviolet irradiation

Abstract This paper presents the results of a study on the effects of deep vacuum and vacuum ultraviolet (VUV) irradiation on polymer сoatings based on thermoplastic polyimide (PI) and tungsten oxide (WO2). Samples from pure PI (without filling) and polymer сoatings with 65 wt% WO2 (PI/WO2) were studied. The VUV irradiation occurred at 125 °C for 24 h, with no more than 10−5 Pa pressure. The VUV radiation intensity was 0.5 W/m2, and the wavelength was 90–115 nm. The total mass loss after VUV treatment for PI was 1.29 wt%, and for PI/WO2 сoating it was 0.63 wt%. The changes in the structure of PI and PI/WO2, established by IR spectroscopy, lead to loosening of the structure of the materials’ surface layers. A decrease in surface microhardness was measured after 24 VUV treatments for PI (12.17 %) and for PI/WO2 сoating (3.68 %), compared to the initial microhardness. It was found that VUV treatment of PI/WO2 сoating lead to an increase in surface roughness, while smoothing (decrease in roughness) of the surface was observed for pure PI.