Numerical and Experimental Investigation on Photothermal Performance of Polyimide/High-Electrical-Performance-Coating Composite Films Considering Surface Roughness

Polyimide (PI) films are the common and important components on spacecraft for thermal control. Their parameter design accuracy has an important impact on the spacecraft thermal balance but there are few studies focusing on the effect of film surface defects. In the present study, photothermal properties of composite films made of PI films and germanium/indium tin oxide/aluminum coatings are obtained by UV-VIS-NIR spectrophotometer. The film surface morphology of composite films is obtained by the atomic force microscope. The present study creatively introduces surface roughness into modeling from the perspective of finite-difference time-domain (FDTD) model. The FDTD method considering surface roughness is used to present a comprehensive investigation on the coating effect on the photothermal properties including transmittance and reflectance of composite films. Based on the random rough surface generated by root-mean-square (RMS) roughness and correlation length, the FDTD method is applied to characterize the electromagnetic field of composite films. It has been found that the numerical accuracy is greatly improved and the numerical results agree well with the experimental data when surface roughness is considered. The results also show that coating material and thickness have remarkable impacts on photothermal properties of the composite films.