Detailed insights of polydimethylsiloxane (PDMS) degradation mechanism via ReaxFF MD and experiments

Abstract

Polydimethylsiloxane (PDMS) serves as a widely used silicone polymer in ablative thermal protection material. Nevertheless, the intricate degradation mechanism governing PDMS at ultra-high temperatures remains unclear. Herein, PDMS pyrolysis was in-depth investigated by employing a combination of experimental methodologies and ReaxFF molecular dynamics (ReaxFF-MD) simulations. PDMS model was firstly validated by product distribution analysis and kinetics analysis. Molecular reaction tracking unveils that the pyrolysis pathway primarily is triggered by the cleavage of the Si-C bond, leading to cyclization reactions and fractures within the Si-O framework at elevated temperatures. The pathways leading to the formation of gaseous, liquid, and solid products during thermal cracking are systematically unveiled. Drawing from these insights, DFT calculations reveal Si-C bond dissociation energies (BDEs) of 98.8, 102.2, and 108.2 kcal/mol for Si-CH3, Si-C2H3, and Si-C6H5, respectively. MD simulations further indicate that the heightened Si-C BDEs across various silicone rubbers impede their decomposition, thereby augmenting the thermal stability of the material. This study augments our comprehension of the PDMS pyrolysis mechanism and offers theoretical insights for enhancing its thermal stability.