Atomistic Scale Analysis of the Carbonization Process for C/H/O/N-Based Polymers with the ReaxFF Reactive Force Field
Summary¶
Carbonization converts polymer precursors into carbon fibers; graphitic domains that emerge during heating strongly influence mechanical properties. The J. Phys. Chem. B article reports an improved ReaxFF parameterization for C/H/O/N chemistry trained against density functional theory data, with particular focus on N\(_2\) formation kinetics and interactions of N\(_2\) with polymer-associated radicals formed during carbonization—extending prior C/H/N-only ladder PAN models that could not treat oxygen-containing precursors. Reactive molecular dynamics then probes initial-stage carbonization for three precursors: idealized ladder polyacrylonitrile (PAN), a modeled oxidized PAN, and poly(\(p\)-phenylene-2,6-benzobisoxazole) (PBO). The abstract emphasizes resolving molecular pathways for low-molecular-weight gas species and all-carbon six-membered ring formation, plus alignment tendencies of ring clusters as prerequisites for further graphitic evolution. The corpus PDF filename indicates a proof; verify pagination against the version of record at the DOI. Maintainer catalog: docs/corpus/NON_PRIMARY_ARTICLE_PAPER_SLUGS.md.
Methods¶
ReaxFF training (A)¶
CHON-2019 improves C/H/O/N ReaxFF using DFT training data, emphasizing N\(_2\) formation kinetics and N\(_2\) interactions with polymer-associated radicals—extending C/H/N-only ladder PAN models that cannot treat oxygenated precursors. Full training reaction lists and optimization workflow: JPCB article + Supporting Information.
Reactive MD protocols (B)¶
RMD (B): Initial-stage carbonization of ladder PAN, oxidized PAN, and PBO; PBC; Berendsen thermostat; 0.25 fs timestep; 10 K/ps ramp to 2800 K; 900 ps NVT; bond-order cutoff 0.3 (authoritative tables on 2019kowalik-j-phys-chem-atomistic-scale and JPCB VOR). System size (atoms): see SI/PDF. Barostat: N/A — NVT after heat-up. Pressure / stress / hydrostatic GPa targets: N/A — not used (constant-volume NVT). Electric field / umbrella / metadynamics / replica exchange: N/A — not used.
Note on this corpus PDF (D)¶
Proof in corpus; use 2019kowalik-j-phys-chem-atomistic-scale for pagination-stable locators.
Findings¶
Mechanisms¶
The refined field enables oxidized PAN within the same C/H/O/N framework as ladder PAN. Trajectories resolve low-molecular-weight gas pathways (including N\(_2\) channels) and six-membered carbon ring formation with cluster alignment trends tied to early graphitic ordering. Precursor-dependent differences among PAN variants and PBO are explicit in the ring/gas statistics.
Limitations¶
Proof PDF; verify VOR for final figure numbering. Shock temperatures exceed typical furnace ramps—mechanistic insight, not direct process kinetics mapping.
Limitations¶
Proof-stage PDF in corpus; verify final pagination and any editorial changes against the version-of-record DOI. High-temperature MD provides mechanistic insight but does not replace continuum furnace models for industrial carbonization schedules.
Relevance to group¶
Develops group ReaxFF capability for realistic C/H/O/N polymer carbonization beyond C/H/N-only ladder PAN models and connects to carbon-fiber precursor chemistry.