Relationship between photofixed condensate, effluent and bulk composition of several common RTV materials

Raman spectroscopy and Fourier Transform Infrared (FTIR) spectroscopy are employed to analyze the bulk compositions of five kinds of Room Temperature Vulcanized (RTV) silicones (CV2568, RTV566, DC93-500, SCV2590 and SCV2590-2) that are commonly employed in orbiting spacecraft. It is found that polydimethylsiloxane (PDMS), silicon dioxide, Tetra-n-propylsilicate (NPS), silicic acid, tetraethyl orthosilicate, and trimethylsilanol are contained in all of them. The outgassing products from those silicones are characterized by FTIR. By comparing the position of the peaks, it is found that the outgassing products of each material are PDMS and NPS which are consistent with the compositions of samples determined with Raman and FTIR respectively. These results indicate that the composition analysis of bulk or thin film silicones with Raman and FTIR could be used as the guideline to predict the outgassing products of silicones. This in turn can lead to a more global approach for determining photofixing issues associated with outgassing. In support of this, the photofixed films from pure PDMS, NPS, and their mixtures were analyzed by spectroscopic ellipsometry and their optical constants were determined