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Water transport in highly cross-linked coatings: pore-to-pore exchange as the governing mechanism
A new simulation study shows that water diffusion in tightly cross-linked polymer networks is governed primarily by the exchange of water between pore clusters, rather than by free volume or network polarity.
Understanding water behaviour in highly cross-linked coatings is essential for durable outdoor performance. Water uptake and release affect swelling, adhesion, corrosion resistance and mechanical stability. This study investigates water dynamics in dense polymer networks and identifies a key parameter: the ability of water molecules to move between connected pore volumes.
Using a multi-scale methodology combining molecular dynamics simulations with experimental validation, the researchers analysed water–polymer interactions, hydrogen-bonding dynamics and the geometry of water clusters. Contrary to common assumptions, free volume and polarity play a secondary role; instead, diffusion is controlled by the connectivity of water clusters.
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Controlling moisture behaviour through molecular design
The findings highlight that the shape, size and continuity of water clusters vary across networks, and that water transport is facilitated by interconnected pore structures. Hydrogen-bond dynamics between water and network components are central to this behaviour. By tailoring polymer architecture, water absorption, trapping and desorption can be adjusted – a promising approach for melamine-curable or other highly cross-linked systems.
The study offers new insights for improving moisture resistance in protective coatings, particularly for outdoor applications requiring long-term barrier performance.
Source: Mousavifard, S. M., Mohseni, M., Yahyaei, H. & Makki, H., Water exchangeability between pore volumes: a key mechanism governing water diffusion in highly cross-linked polymer coatings. Progress in Organic Coatings 207, 109405 (2025).
