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Investigating structure–property relations of poly(p-phenylene terephthalamide) fibers via reactive molecular dynamics

Summary

Reactive MD with ReaxFF is applied to poly(p-phenylene terephthalamide) (PPTA, Kevlar-class) fiber models with varying radius, crystallinity, and core–shell arrangements, motivated by aramid fibers’ high specific stiffness and the need to connect atomic texture to macroscopic modulus. Quasi-static tensile deformation up to ~15% strain extracts Young’s moduli and follows how crystalline versus disordered fractions and domain boundaries control failure initiation. The manuscript introduces an order parameter based on the cross-sectional area fraction of crystalline domains to rationalize modulus trends in core–shell geometries where skin and core order differ by construction.

Methods

MD application (ReaxFF, quasi-static tension): Reactive MD with ReaxFF pulls PPTA fiber supercells in quasi-static tension to ~15% strain along the fiber axis; step size and relaxation between strain increments are specified in papers/ReaxFF_others/dyilmaz.pdf. Stress–strain curves give Young’s modulus at small strain and mark bond-scission. Crystalline and disordered domains are labeled so a cross-sectional area fraction of ordered material can define an order parameter for core–shell geometries. Engine / timestep / thermostat / total trajectory time: N/A — not recoverable from the short corpus text available here (read the PDF for LAMMPS or other engine keywords and control parameters). Ensemble label during tension ramps: N/A — not stated in the indexed extract (likely quasi-static energy relaxation between strain steps rather than long NVT production segments; confirm in PDF). Barostat / hydrostatic pressure control: N/A — not used for the quasi-static uniaxial protocol summarized here. Imposed pressure (GPa/MPa): N/A — tensile load along fiber axis, not a pressure-driven study. Electric field / enhanced sampling: N/A — not used.

Target temperature (K) during tension / relaxation segments: N/A — not stated in the indexed extract; confirm whether runs are 0 K energy minimization steps vs finite-T MD in papers/ReaxFF_others/dyilmaz.pdf.

Force-field training: N/A — applies an existing organics-capable ReaxFF cited in the manuscript rather than reporting a new fit.

Static QM / DFT: N/A — not the primary method in the summarized framing.

PBC / supercell: 3D PBC fiber supercells as in standard bulk fiber models; cell vectors and equilibration/production durations: N/A — see PDF if not tabulated in your local extract.

Findings

The abstract reports Young’s moduli of about 226 GPa (disordered chains) versus 311 GPa (crystalline chains) for the illustrated models, attributing the gap to order. For core–shell fibers where core and shell swap crystalline vs underordered assignments, effective moduli scale approximately linearly with the cross-sectional area fraction of the crystalline section; the authors introduce an order parameter to capture this trend. Failure initiates at domain boundaries between ordered regions rather than through uniform bulk chain rupture, so strain up to ~15% probes how texture concentrates load. Bibliography: this corpus copy is a dated manuscript PDF without a recorded DOI; reconcile with any journal version before citing pagination. ReaxFF organics models may not reproduce macroscopic Kevlar tests quantitatively—use the PDF for tables and failure sequences.

Limitations

  • DOI not recorded in normalized metadata; treat bibliographic details as manuscript-stage until reconciled with a published version.
  • Strain rate, system size, and ReaxFF organics parameter scope imply qualitative trends for ultimate properties more than quantitative agreement with macroscopic fiber tests.

Relevance to group

Demonstrates ReaxFF uptake in aramid fiber mechanics adjacent to the group’s broader reactive polymer / composite interests (even though Penn State authors are not listed on this PDF). Operators curating PPTA should cross-check any future DOI assignment against the published record if this manuscript PDF is superseded by a journal version with identical science.

Citations and evidence anchors

  • Abstract and introduction in papers/ReaxFF_others/dyilmaz.pdf (dated Feb 3, 2016 in the extract).