Randomly Alkylated POSS as Atomic Oxygen-Protective Coating Materials for Low Earth Orbit Satellites

Atomic oxygen (AO), a predominant species in the residual atmosphere of low Earth orbit (LEO), poses a significant threat to satellites due to its high chemical reactivity. Although polyhedral oligomeric silsesquioxane (POSS) derivatives have been utilized as AO-protective coating materials, the fabrication of uniform and crack-free films remains challenging. To improve film-forming properties, we designed and synthesized a randomly alkylated POSS molecule (C 8 C 10 C 12 C 14 -POSS), which incorporates various alkyl groups (C 8 H 17, C 10 H 21, C 12 H 25, and C 14 H 29 ) into its side chains. Compared with octyl-substituted POSS (C 8 -POSS), C 8 C 10 C 12 C 14 -POSS exhibited superior film uniformity when applied via spin-coating. The AO resistance of these films was evaluated using a laser-detonation AO beam. After exposure of 7 × 10 20 atoms/cm 2 of AO, microbalance measurements showed that the mass loss of C 8 C 10 C 12 C 14 -POSS was comparable to that of C 8 -POSS. Additionally, X-ray photoelectron spectroscopy measurements further revealed that the silica layer formed on C 8 C 10 C 12 C 14 -POSS was thinner than that on C 8 -POSS, and the composition gradient was more gradual in the depth direction between the silica layer and the underlying C 8 C 10 C 12 C 14 -POSS layer. Scanning electron microscopy observations confirmed the absence of physical defects on the surface of C 8 C 10 C 12 C 14 -POSS after AO exposure. These findings demonstrate that using POSS to incorporate randomly distributed alkyl groups is an effective molecular design strategy for developing AO-protective coating materials, enabling nanoscale control of silica layer formation and suppressing microscale crack generation. This approach can enhance the long-term durability and reliable operation of satellites in LEO and very LEO environments.