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Moderate hydrophobicity boosts epoxy anticorrosion performance
A new study challenges the assumption that maximum hydrophobicity equals maximum corrosion protection. Researchers show that epoxy coatings achieve optimal anticorrosion performance at a moderate water contact angle of 140°, where the competition between hydrophobic and aerophilic behaviour is balanced.
Hydrophobic coatings have long been associated with improved anticorrosion performance, with development efforts often aimed at maximising water contact angles. A recent investigation, however, demonstrates that this assumption does not hold universally. The researchers prepared a series of epoxy resin coatings with systematically varied hydrophobicity and discovered a non-monotonic relationship between water contact angle and corrosion resistance, with performance first increasing and then declining as hydrophobicity rose.
The optimum corrosion resistance was identified at a water contact angle of 140°, rather than at the highest achievable value. Coatings at this balanced point showed an improvement in corrosion resistance of approximately one order of magnitude over the most hydrophobic samples in the series.
Competition between hydrophobic and aerophilic behaviour
Density functional theory (DFT) calculations revealed the underlying mechanism. Strongly hydrophobic surfaces tend to attract more air, leading to enhanced adsorption of oxygen molecules at the coating–substrate interface, which accelerates corrosive processes. In contrast, moderate water adsorption was found to optimise the repulsion of adsorbed oxygen species, limiting the simultaneous availability of H2O and *O at the substrate and thus suppressing corrosion. The findings highlight that surface wettability and anticorrosion performance are linked through a dynamic equilibrium rather than a simple linear correlation.
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Implications for durable protective coatings
Experimental characterisation confirmed that coatings with moderate hydrophobicity effectively cover microstructural defects, reduce electrolyte penetration pathways and prevent excessive oxygen accumulation. As a result, they exhibit higher resistance values and superior long-term stability in accelerated salt spray ageing tests. The authors conclude that the design of durable anticorrosive coatings should move beyond the pursuit of extreme hydrophobicity and instead target a balanced wettability state. This perspective offers a theoretically grounded route for the development of next-generation epoxy-based protective systems.
Source: Ma, H. et al., Epoxy resin coatings with the competitive relationship of hydrophobic and aerophilic towards anticorrosion application. Progress in Organic Coatings, 110095 (2026).
