Skip to content

Harnessing chain mobility via protonation for tough and isotropic hydrogel

Summary

Ultra-tough, isotropic poly(vinyl alcohol) hydrogels are prepared by sequential acidification, freeze-thawing, and salting-out. Reactive MD with a ReaxFF C/H/O/Li/Na/K/Cl/I parametrization (reparameterized from prior reports) probes protonation and hydrogen-bond network evolution for a PVA dimer in water versus HCl solution, alongside DFT (Jaguar) checks on hydrogen-bond strengths in model dimers and experimental mechanics and microstructure.

Methods

Primary source: papers/Shi_Si_Lin_Mao_Hydrogel_Advanced_Materials_2026.pdf.

Experimental. PVA hydrogels processed with controlled HCl in precursor, freeze-thaw (FT) and salting-out (SO) steps; mechanical testing (tensile, fatigue, notch tests), SEM, DSC, SAXS, mercury porosimetry, optical and FLIM imaging, NMR on protonation, and extended protocols in Supporting Information.

Reactive MD. ReaxFF C/H/O/Li/Na/K/Cl/I (reparameterized from cited ReaxFF electrolyte-water and biomolecule work). PVA dimer with 20 OH groups in neutral water versus acidic HCl solution: initial NVT equilibration at 300 K for 2.0 ns; second NVT segment at 253 K for 2.0 ns to capture low-temperature hydrogen-bond network evolution. Three replicate trajectories for hydrogen-bond statistics as stated. Additional dry C3H7OH dimer minimizations compare ReaxFF and DFT hydrogen-bond strengths for defined protonation cases; Mulliken charge analysis on shared protons with increasing explicit water molecules.

DFT. Non-periodic Jaguar DFT calculations on small alcohol dimers for hydrogen-bond energetics in neutral and protonated cases.

Association modeling. Flory-Huggins lattice hydrogen-bond counting (Text S2 in SI) ties acid concentration to PVA-PVA versus PVA-water hydrogen-bond populations.

1 — MD application (atomistic dynamics). LAMMPS ReaxFF molecular dynamics of a PVA dimer (20 OH groups) in H₂O vs HCl (order ~100+ atoms with solvation per PDF); 3D PBC; two 2.0 ns NVT stages at 300 K and 253 K with Berendsen or Nose–Hoover thermostat (per SI); 3 replicate trajectories; fs time step in the PDF (not on this one-line blurb). N/A — NPT barostat for the PVA-dimer line. N/A — static E-field in MD. N/A — replica or metadynamics. Flory-Huggins in Text S2 is lattice (not MD).

2 — Force-field training (application of reparametrized C/H/O/Li/Na/K/Cl/I ReaxFF from cited lines). N/A — this paper reuses/extends a prior ReaxFF with Jaguar DFT spot checks on dimers.

3 — Static QM / DFT (Jaguar dimer H-bond energetics). See DFT paragraph. 4 — Review — N/A.

Findings

  • Reported optimized PVA-SO hydrogel reaches tensile strength 29.5 MPa, stretchability 2683%, and toughness 424 MJ m^-3 among isotropic hydrogels in the article's comparison.
  • MD shows acid-catalyzed proton transfer forming H3O+ and protonated PVA-OH2+, with greater chain curling in acid at 253 K versus neutral water and similar inter-chain hydrogen-bond counts when protonated sites are included, supporting homogenized chain conformations before salting-out fixes dense hydrogen-bonded domains.
  • DFT validates qualitative ReaxFF trends for dimer hydrogen-bond strengths in selected cases; the manuscript notes explicit limits of gas-phase dimer models versus full solvation dynamics.

  • Experiments correlate acidification with reduced premature crystallization during freeze-thaw, higher transparency, and modulated pore and crystallinity signatures before salting-out builds tough networks.

  • Caveat / comparison: DFT dimer gas-phase models vs full solvated MD—see ## Limitations and the manuscript on solvated network mechanics.

Limitations

Residual salt and dehydration sensitivity are noted in the article as practical limits; ReaxFF provides qualitative protonation and HB trends with DFT spot checks.

Relevance to group

Adri van Duin contributes reactive MD and DFT validation of protonation and hydrogen-bond behavior for the PVA processing hypothesis.

Citations and evidence anchors

DOI: 10.1002/adma.202517407.