A molecularly impermeable polymer from two-dimensional polyaramids
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Article Date: 2025-11-12
Article URL: https://www.nature.com/articles/s41586-025-09674-9
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Summary
This paper reports the synthesis, characterisation and gas-barrier performance of a two-dimensional polyaramid (2DPA-1). The authors produce powders and thin films (down to a few nm thick) and apply an array of techniques — NMR, TEM, ATR‑FTIR, Raman, gas adsorption, bulge tests (AFM and an optical interferometric method), TGA‑MS, DFT/MD simulations, Monte Carlo and kinetic protection tests on perovskite films — to show that stacked 2DPA-1 platelets form mechanically robust films with exceptionally low molecular permeability. Key experimental observations include long-lived pressurised bulges (days to months), extremely low derived permeabilities for O2/H2O from perovskite-degradation experiments (~3.3×10−8 Barrer), chemical stability to protic solvents and humidity, and DFT/MD evidence for large translocation energy barriers that depend on interlayer offset.
Key Points
- 2DPA-1 synthesis: a solution-phase condensation of TMC and melamine in NMP/TFA followed by purification yields yellow–orange platelets; stirring time controls the platelet size parameter r.
- Characterisation: NMR (in TFA), TEM, ATR‑FTIR and Raman confirm amide linkages and triazine motifs; simulated spectra from ab initio MD match experiments and help assign vibrational bands.
- Physical properties: powder BET ≈ 74 ± 10 m2 g−1 with mesopores (~11 nm) attributed to interparticle gaps; platelet density estimated at 1.14 ± 0.09 g cm−3.
- Chemical stability: no notable transamidation after 9 h in TFA; negligible hygroscopic chemical change after ~539 days in water; thermal degradation yields water (amide cleavage) only at high T (300–450 °C).
- Gas impermeability: suspended 2DPA-1 films (4–35 nm) form persistent bulges that can remain inflated for days to months, inconsistent with Knudsen- or effusion-based leak pathways and indicating extremely low permeability through the unit-cell pores.
- Quantified barrier performance: analysis of perovskite (MAPbI3) degradation under ambient conditions with and without 60 nm 2DPA-1 protection yields a 2DPA-1 diffusivity for reactive gases of ≈2.93×10−20 m2 s−1 and permeability ≈3.3×10−8 Barrer (O2/H2O proxy).
- Mechanism (modelling): DFT and umbrella-sampling MD show large translocation energy barriers for CO2, N2 and Ar across bilayers; Monte Carlo geometric models indicate pore overlap and interlayer offset control permeation pathways.
- Measurement advances: the team developed an optical interference/RGB method to extract bulge deflection in environmental chambers (complements AFM) and validated it against AFM and theoretical models.
- Practical demonstration: 2DPA-1 coatings slow MAPbI3 perovskite degradation, showing potential as ultrathin barrier layers for sensitive optoelectronic devices.
Content summary
The authors describe a robust workflow from synthesis to application. They synthesise 2DPA-1 via irreversible amide formation, purify platelets and form thin films supported on polystyrene for transfer. Comprehensive spectroscopic and microscopic characterisation confirms the 2D polymeric structure and orientational ordering in thin films. Gas sorption shows meso/macroporosity is largely interparticle. AFM bulge tests — and a novel optical fringe/RGB approach — measure deflection decay and resonance while carefully accounting for rim-seal leakage. The persistence of bulges and the lack of thickness dependence in deflation rates argue against macroscopic leak pathways; instead, transport is dominated (and effectively blocked) by the polymer unit-cell architecture. DFT/MD energy profiles and umbrella-sampling PMFs reveal high barriers for gas translocation that depend on layer offsets; Monte Carlo and confined-diffusion analyses support steric exclusion when platelets stack with modest misalignment. Finally, coating MAPbI3 perovskites with 2DPA-1 dramatically slows the XRD-evidenced formation of PbI2, enabling an experimental estimate of gas diffusivity and permeability through the film.
Context and relevance
Gas-impermeable, atomically thin or molecularly-tight polymer films are a major target for flexible electronics, packaging and encapsulation of air-/moisture-sensitive devices (for example perovskite photovoltaics). This work demonstrates a chemically robust 2D polymer that combines irreversible amide chemistry with platelet stacking to achieve practical, ultrathin barrier films. The combination of rigorous experiment, advanced optical/AFM measurement, kinetics on real devices and multiscale modelling makes the case compelling: 2DPA-1 is a promising route to molecular-level impermeability that is compatible with solution processing and thin-film device fabrication.
Why should I read this?
Short and frank: if you care about making ultrathin barriers that actually stop oxygen/water getting into stuff — batteries, perovskites, sensors — this paper is gold. The authors not only show a new 2D polyaramid that stays chemical and mechanically stable, they also prove it slows down real device degradation and give you the numbers and models to understand why. Nice blend of hands-on experiments and simulations — saves you a lot of head-scratching.
Author style
Punchy — the paper pairs solid experimental demonstrations with multiscale theory; for researchers and engineers working on encapsulation, membranes or 2D polymers this work is highly relevant and worth reading in detail to replicate or adapt the methods (especially the bulge/optical measurement and the perovskite-protection protocol).