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Thermodynamic exclusion of alkaline ionic crystals from polymers and interfacial-controlled subcritical water degradation
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Z
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J
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DOI：10.1016/j.ces.2026.123853.png)
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Abstract
En 中文
Alkaline subcritical water is a promising medium for depolymerizing condensation polymers, yet kinetic interpretations remain conflicted because the spatial distribution of alkaline catalysts at polymer-water interfaces has been largely assumed rather than resolved. Here molecular dynamics simulations and free-energy analyses show that alkaline ionic species, exemplified by KOH, are thermodynamically excluded from polymer bulk phases, including both crosslinked epoxy networks and molten linear polyesters and polyamides. Water, in contrast, permeates polymers to an extent governed by functionality and topology, producing a universal microscopic asymmetry of water uptake coupled with alkali exclusion. Solvation and transfer free energies quantify a strong driving force for ion expulsion into the aqueous phase, while transport analyses indicate that any ions initially trapped within polymers exhibit sluggish escape. Incorporating these constraints into kinetic simulations demonstrates that exogenous-base-activated depolymerization must be interfacial and is captured by shrinking-core or reaction-shell models, whereas systems dominated by water autoionization can approach pseudo-homogeneous kinetics. This framework unifies disparate kinetic observations and provides a physically grounded basis for designing hydrothermal recycling processes by coupling catalyst speciation and interfacial accessibility.
Keywords:
Alkaline subcritical water
Chemical recycling
Thermoset depolymerization
Thermodynamic exclusion
Molecular dynamics
Shrinking-core kinetics
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