Atomistic-Scale Simulations of the High-Temperature Chemistry of Si/C/O/H-Based Polymers and Their Conversion to Si/C Solid Materials

This study investigates the pyrolysis behavior of polydimethylsiloxane and its modified analogs─PolyTrimethylSiloxane (PTMS), PolyEthylTriMethoxySilane (PETMS), and PolyDimEthylTriMethoxySilane─through molecular dynamics simulations utilizing the ReaxFF reactive force field. The research aims to understand how variations in carbon and oxygen contents influence the decomposition pathways and material properties essential for synthesizing silicon carbide (SiC), a material of growing technological importance. Our simulations conducted at temperatures ranging from 2000 to 3000 K revealed the formation of SiC nanoparticles and silica nanoclusters, alongside various small-molecule byproducts, including hydrocarbons, aldehydes, and carbon monoxide (CO). The ratio of the total mass of large silicon (Si) clusters to small molecules was higher at a lower temperature of 2000 K than at 3000 K. PTMS at 2000 K achieved a maximum mass ratio of 5.4. An 8-fold larger PETMS system was simulated to further explore these findings, confirming similar patterns in small molecule formation and cluster distribution. Radial distribution function analysis of the large clusters indicated amorphous solids composed of Si/C/H/O, with no signs of crystallization upon cooling from 3000 K. The results suggest that these clusters remain in a high-viscosity, glass-like state, with limited crystallization observed. Overall, this research enhances our understanding of decomposition mechanisms in polymer precursors and emphasizes the potential of these materials for advanced manufacturing applications, particularly in the production of high-temperature SiC ceramics. These insights pave the way for the design of novel polymer precursors with improved properties and inform future experimental endeavors in silicon-based ceramics for additive manufacturing.