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

Polymer-derivedceramics are a promising class of high-temperaturematerials. This work uses LAMMPS and reactive force field (ReaxFF)energy potential to first-time quantify the atomic evolution of thepolymer-to-ceramic conversion. Three different polymer structuresare selected based on initial carbon content and molecular structuredifferences. 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 availableotherwise. 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 significantC-C bond formation during C-H bond loss. The end structureshave vastly different Si-O-rich and C-rich domain sizes, whichcannot be observed by any bulk analysis. For the first time, H presenceand cluster separation are shown to be determined by the polymer molecularstructure. The RDF results show that higher pyrolysis temperatureleads to more C-C bond formation. Even at 2100 K, C-Hbonds are still prevalent and there is no long-range ordering. Suchfundamental understanding provides new knowledge about polymer atomicevolution to silicon oxycarbide (SiOC) ceramics.