Molecular Dynamics Simulations of Proton Diffusion in the Short-Side-Chain Perfluorosulfonic Acid Ionomer
Bibliographic record
Abstract
This computational study seeks to understand why low equivalent weight short-side-chain (SSC) perfluorosulfonic acid membranes exhibit higher proton conductivities than Nafion when hydrated at similar water contents. The diffusion of protons in the SSC ionomer at water contents of 3, 6, and 13 H2O/SO3H were investigated through classical molecular dynamics simulations. We developed a unique force field set based on torsion profiles derived from extensive electronic structure calculations of a two side chain fragment of the SSC ionomer and simulated a system consisting of a single 40 repeat unit of the polymer (F3C-{[CF2-CF(OCF2CF2SO3H)]-(CF2CF2)3}40-CF3) corresponding to an equivalent weight of 578 at each of the three water contents. After an equilibration time of approximately 450 ps at 300 K where the density was fixed at 1.67 g/cm3, structural information was collected from 2 ns production runs at 315C. We calculated proton (as a hydronium ion) diffusion coefficients of 2.83×10-7, 1.37×10-6, and 3.87×10-6 cm2/s at the three water contents which show excellent agreement to experimentally measured diffusion coefficients at the lower water content only.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.002 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".