danieldelgadouriarte.comresearch summary

Research summary · polymers and molecular simulation · Published

H₂/CH₄ transport in polyethylene, and building polymer models for molecular dynamics

Daniel Delgado Uriarte’s first-author paper with A. López in ACS Applied Polymer Materials (2026): how hydrogen and methane diffuse through amorphous polyethylene, and how much the answer depends on the simulation ensemble.

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Oblique view of five polyethylene chains, each in its own colour, inside a periodic simulation box
Figure. POLYMER-FLOW quick test, final snapshot: five polyethylene chains, 200 united-atom sites, one colour per chain, inside the periodic box (dashed). Bonds that cross the box boundary are not drawn. A visualization of an archived prototype run, not a validated material model.

In plain language

Molecular dynamics follows every molecule in a small box of material to see how gases move through it. For hydrogen and methane in amorphous polyethylene, the study compares temperatures and simulation ensembles and checks the results statistically.

The result in the title: the diffusivity selectivity between H₂ and CH₄ depends on the ensemble chosen for the simulation. The study began as the bachelor’s thesis at Universidad de Deusto and UPV/EHU.

What is new

  • A statistically validated molecular dynamics study of H₂/CH₄ transport in amorphous polyethylene, comparing temperature and simulation ensembles.
  • Published with its code: github.com/danieldelgadouriarte/pe-h2-ch4-md.
  • POLYMER-FLOW: every molecular-dynamics study of a polymer starts by building and equilibrating the material again. POLYMER-FLOW turns that into one declarative specification (polymer, chain length, number of chains, force field, temperature, pressure and acceptance criteria). It grows and packs the chains, compresses and anneals them, checks density, stationarity and bonds, and returns a LAMMPS data file ready to simulate.

Data used

  • Molecular dynamics of amorphous polyethylene with H₂ and CH₄; the code is public in the repository above.
  • POLYMER-FLOW quick test shown in the figure: five polyethylene chains, 200 united-atom sites.

Status

Published. Delgado-Uriarte, D., & López, A. (2026), ACS Applied Polymer Materials. POLYMER-FLOW is a prototype, polyethylene only so far; more polymers and validation against experimental densities are pending. Related studies in progress: asphaltene-reinforced nanocomposites (manuscript under revision) and gas barriers in nanocomposites.

How to cite

Delgado-Uriarte, D., & López, A. (2026). Ensemble-dependent diffusivity selectivity in amorphous polyethylene: a statistically validated molecular dynamics study of H₂/CH₄ transport. ACS Applied Polymer Materials. https://doi.org/10.1021/acsapm.6c00287

Volume, issue and page numbers: see the DOI link, which always points to the publisher’s current record.

Work on this together

If you work on gas transport in polymers, polymer liners or membranes, or need equilibrated polymer models for LAMMPS, propose a joint study or try POLYMER-FLOW on your polymer.

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