ReaxFF Simulation of Pyrolysis Behaviors of Polysiloxane Precursors with Different Carbon Content

Polymer-derived ceramics are a promising class of high-temperature materials. This work uses LAMMPS and reactive force field (ReaxFF) energy potential to first-time quantify the atomic evolution of the polymer-to-ceramic conversion. Three different polymer structures are selected based on initial carbon content and molecular structure differences. From these simulations, the ceramic composition, yield, atomic structure, bond change, and radial distribution function (RDF) are comprehensively analyzed and provided data that are not available otherwise. The ceramic compositions correlate with the polymer compositions. The C-rich precursor forms C–C bonds through Si–O, Si–C, and C–H bond losses while less C-rich polymers have no significant C–C bond formation during C–H bond loss. The end structures have vastly different Si–O-rich and C-rich domain sizes, which cannot be observed by any bulk analysis. For the first time, H presence and cluster separation are shown to be determined by the polymer molecular structure. The RDF results show that higher pyrolysis temperature leads to more C–C bond formation. Even at 2100 K, C–H bonds are still prevalent and there is no long-range ordering. Such fundamental understanding provides new knowledge about polymer atomic evolution to silicon oxycarbide (SiOC) ceramics.