The stability of polymethylphenylsiloxane varnish modified with SiO2 nanoparticles and exposed to solar spectrum quanta

The article is focused on the effect of modification with silicon dioxide nanoparticles on the stability of polymethylphenylsiloxane varnish exposed to solar spectrum quanta. The modification was carried out within 0.1–10 wt % of SiO₂ by mixing the varnish with toluene and nanopowder and by subsequent application of ultrasonic waves in order to obtain the even distribution of nanoparticles. The irradiation was performed using a xenon arc lamp with the intensity 3 times higher than solar radiation. The analysis included studying the diffuse reflectance spectra within 0.2–2.5 μm; the optical absorption edge; the solar absorptance; FTIR and XRD spectra obtained after modifying and irradiating the samples; the adhesion of the samples to the aluminum-magnesium alloy substrate. Irradiation of the varnish leads to the appearance of integral absorption band from 295 to 700 nm, which is determined by the radicals formed by irradiation upon after breaking of the chemical bonds Si–Si, Si–C, C–C, C–O, CH₂–H, C–H, and Si–O. The results allowed for determining the optimal concentration value for SiO₂ nanoparticles that provides a 1.3-fold increase in the photostability of optical properties. The resulting modified varnishes can be used to develop thermal control coatings for spacecraft and photostable coatings for solar industry.