Covalently bound self-passivating silica layer enhances polyetherimide stability in harsh space conditions

The rapid expansion of human space exploration highlights the need for advanced materials capable of enduring the severe conditions of extraterrestrial environments. Polymeric materials, such as polyetherimide (PEI), are extensively used in aerospace applications due to their low density, mechanical versatility, and partial shielding capacity against radiation. Nevertheless, prolonged exposure to hostile factors such as galactic cosmic rays, solar energetic particles, solar wind ions, atomic oxygen, and electromagnetic radiation results in progressive structural degradation manifested as erosion, mass loss, and deterioration of mechanical, thermal, and optical properties. To mitigate these effects, inorganic protective layers, particularly metal oxides, have been investigated because of their high hardness, chemical stability, and erosion resistance. Despite these advantages, issues related to interfacial adhesion and long-term stability of such protective layers remain significant challenges. The present study reports a novel covalent silica-based passivation approach for PEI, achieved through a multi-step chemical functionalization of the polymer surface. The process involves: i) the partial hydrolysis of imidic ring on PEI film surface, forming polyamic acid (PAA) layer; ii) chemical reduction of the carboxylic acid of PAA to benzylic alcohol groups; iii) grafting tetraethyl orthosilicate to benzyl alcohol moieties. The procedures were monitored using ATR-FT-IR, DSR-UV-Vis, contact angle, and SEM-EDX analyses. To evaluate the shielding efficacy of the obtained system, both pristine PEI and silica-coated PEI samples were exposed to simulated fast solar ions flux. The experimental results confirm the increased resistance to erosion of the silica shielded material compared to that of untreated PEI. Finally, to assess the applicability of the material in real-scenarios, a computer simulation was performed to estimate the energy dose for the proposed material as a function of the radius for different space orbits.