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Joint theoretical and experimental study of stress graphitization in aligned carbon nanotube/carbon matrix composites

Corpus note

The repository contains a galley PDF; cite the version of record using the DOI below for bibliographic permanence. Maintainer catalog entries for SI/galley/proof roles: NON_PRIMARY_ARTICLE_PAPER_SLUGS.md.

Summary

The work combines ReaxFF-based reactive molecular dynamics (RMD) with experiments on aligned carbon nanotube (CNT) / polyacrylonitrile (PAN)-derived carbon matrix composites to explain stress graphitization at CNT–matrix interfaces during high-temperature treatment. The motivation is that graphitic domains around CNTs can strengthen the matrix, but the atomistic drivers of stress-assisted carbonization during pyrolysis are not obvious from continuum descriptions alone. Adri C. T. van Duin is a corresponding author on the computational line of the study. The abstract contrasts CNT-free versus CNT-reinforced models and reports that simulations at 1500 K reproduce a stress concentration pattern that promotes nitrile orientation, dehydrogenation, and carbon six-membered ring formation near CNT surfaces, paralleling TEM-visible graphitic layers in processed films.

Methods

Corpus note: The checked-in file is a galley PDF; DOI 10.1021/acsami.3c03209 is the bibliographic anchor for pagination-sensitive citations.

1 — MD application (ReaxFF in LAMMPS, CNT / oxidized-PAN, stress graphitization)

  • Engine / code: ReaxFF RMD in LAMMPS; VMD for snapshots (ACS Appl. Mater. Interfaces Methods).
  • Ensemble, timestep, PBC, thermostat: NPT and NVT stages use 3D PBC; time step 0.25 fs; Nose–Hoover-style coupling (article reports 100 fs temperature/pressure coupling constants for the NPT preequilibration of the orthorhombic box); bond order 0.3 for chemistry parsing in the RMD setups (see the AMI Methods in the corpus galley PDF).
  • Heating / graphitization: Three CNT-loading cases (0, 20, 80 wt% in the abstract-level narrative) with 1D aligned tubes; from separate preequilibrated NPT snapshots the authors take three independent seeds each and heat/carbonize at 1500 K in NVT for 5 ns to study stress-driven local graphitization (Methods; align to the galley for all stage lengths and NPT T).

  • Analysis: Local stress (von Mises-type, as defined in-text) and chemical order parameters tie higher CNT loading to larger peripheral stress and faster dehydrogenation/ring-formation in the PAN-derived carbon (see main text + SI for all definitions). N/A in this short note for a reprint of every NPT stage not shown above—see the VOR + SI when galley line wrap differs.

  • Barostat, electric field, rare-event sampling: NPT preequilibration and NVT 1500 K carbonization as quoted; N/A for E-field; N/A for metadynamics; N/A for a separate NPT barostat during the 5 ns NVT 1500 K carbonize (constant-T MD in NVT).

2 — Experiments (CNT array / PAN, mechanical testing, TEM)

CNTs (multiwall, ~2–3 walls, 4–7 nm diameters, per Methods), PAN precursor, film infiltration/pyrolysis routes as reported; tensile tests (82%/144% gains in tensile strength/Young’s modulus vs a control in the abstract); TEM of graphitic layers on CNTs (see AMI for sample history).

Findings

The simulations relate higher CNT loading to stronger stress concentration near CNT surfaces, which biases nitrile alignment and accelerates local carbonization/graphitization pathways relative to lower-loading or CNT-free models in the same thermal window. Experimental films show additional graphitic layers forming from the PAN-derived matrix around CNTs, with large improvements in tensile strength and Young’s modulus (reported at 82% and 144%, respectively, in the abstract relative to the chosen baseline). Together, the computational and laboratory results support a stress-mediated graphitization mechanism for engineering CNT/carbon-matrix interfaces in high-temperature processing.

Limitations

Process details (exact reactor schedules, full mechanical test statistics, and all imaging conditions) should be taken from the full PDF/SI beyond the first-page extract.

Relevance to group

Demonstrates ReaxFF applied to polymer-derived carbon and nanocarbon composite processing with experimental validation, consistent with the group’s reactive carbonization portfolio.

Citations and evidence anchors

  • DOI: 10.1021/acsami.3c03209