Modulation of the photothermal degradation of epoxy upon ultraviolet irradiation by polyhedral oligomeric silsesquioxane: a multiscale simulation study

Abstract

Polyhedral oligomeric silsesquioxane (POSS) nanocomposites that improve the ultraviolet (UV) resistance without affecting the transmittance and mechanical properties of the crosslinked epoxy are in the spotlight. In this study, the structural role of POSS nanofillers in the UV resistance of epoxy was theoretically examined using multiscale analysis that integrates classical molecular dynamics and density functional theory. Under deep-UV irradiation, POSS contributes to the energy dissipation of photothermally excited vibrations rather than its role as a photochemical UV absorber. The intrachain energy transfer modulated by POSS suppresses network chain scission and reduces the rate of fragmentation events. In particular, the unique molecular network structure constructed by POSS inhibits fragment aggregation and prevents the morphological collapse of nanocomposites, such as pore growth and phase separation. The proposed mechanism elucidates the fundamental principle of UV resistance improvement owing to POSS insertion in terms of photothermal reaction-induced thermodynamics.