Degradation mechanism of hydrophobicity in gamma-irradiated Sol-Gel silica films

In laser-driven inertial confinement fusion (ICF) facities, sol-gel derived silica antireflective films have been widely prepared on optical components to improve the laser transmission performance. Current researches indicate that long-term exposure of final optical assemblies in high-power laser systems can lead to the degradation of anti-pollution performance, directly affecting the high-flux output of the laser facities. However, the underlying mechanisms remain unclear. Therefore, we conducted a multiscale investigation combining macroscopic wettability analysis with nanoscale structural characterization. Contact angle measurements demonstrated a systematic hydrophilicity shift ( Δ θ > 50 ° ) accompanied by a 139 % increase in surface free energy following gamma irradiation. High-resolution surface metrology via white light interferometry (WLI) confirmed roughness stability across irradiation doses up to 1000 kGy , while scanning electron microscopy (SEM) imaging revealed stochastic crack formation. Crucially, controlled experiments on geometrically ideal substrates established that such nanoscale topographical defects contribute minimally to wettability alterations, decisively shifting focus to chemical modification mechanisms. X-ray photoelectron spectroscopy (XPS) analysis revealed a notable decrease in relative carbon content from 18.96 % to 14.85 % as radiation dose increased from 0 kGy to 1000 kGy . Combined with the observation that hydrophobicity in non-irradiated samples primarily originates from surface-grafted hydrophobic groups (-CH 3 ), this confirms radiation-induced degradation of hydrophobic moieties as the key mechanism driving the hydrophobic-to-hydrophilic transition. This work elucidates the physicochemical mechanisms of surface contamination of the optical components in high-power laser systems, providing theoretical foundations for optimizing radiation resistance in antireflective films.