Thermo‐Optical Properties of Polysiloxane Coatings for Aerospace Applications

Polysiloxane coatings are prepared by plasma‐enhanced chemical vapor deposition with different O 2 /hexamethyldisiloxane (HMDSO) flow ratios. Higher O 2 content promotes SiO cross‐linking while reducing CH 3 groups, resulting in compromised flexibility. The solar absorptance is almost unaffected by O 2 content and remains a low constant value. The hemispherical emittance increases in a step‐like growth by more than twofold in value. These observed thermo‐optical properties arise from high transmittance of the polysiloxane coatings within the visible to near‐infrared spectrum, coupled with multiple absorption bands in the mid‐ to far‐infrared regions. Crucially, the intensity of several key absorption bands demonstrates a positive correlation with the concentration of SiO bonds in the coatings. Specific to polysiloxane coatings with good flexibility prepared under low O 2 conditions (O 2 /HMDSO = 0.32), the solar absorptance experiences oscillations caused by optical interference effect as coating thickness increases, and then stabilizes after coating thickness reaches ≈3 μm. Hemispherical emittance rises rapidly with the increase of coating thickness until 3 μm and then creeps up after that. These characteristics demonstrate the potential of polysiloxane coatings for precisely tailoring the emittance of space passive thermal control materials, especially their expanded applications on low Earth orbit spacecraft due to excellent atomic oxygen resistance.