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 (C8C10C12C14-POSS), which incorporates various alkyl groups (C8H17, C10H21, C12H25, and C14H29) into its side chains. Compared with octyl-substituted POSS (C8-POSS), C8C10C12C14-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 × 1020 atoms/cm2 of AO, microbalance measurements showed that the mass loss of C8C10C12C14-POSS was comparable to that of C8-POSS. Additionally, X-ray photoelectron spectroscopy measurements further revealed that the silica layer formed on C8C10C12C14-POSS was thinner than that on C8-POSS, and the composition gradient was more gradual in the depth direction between the silica layer and the underlying C8C10C12C14-POSS layer. Scanning electron microscopy observations confirmed the absence of physical defects on the surface of C8C10C12C14-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.