Study on Moisture Diffusion Characteristics and Influencing Factors of Organic Coatings Based on Langmuir‐Type Diffusion Model

Water serves as a primary corrosive medium in the service of protective coatings. To understand the mechanisms and factors controlling water transport in organic coatings, polyurethane coatings with varied microstructures were prepared by adjusting diluent content. These coatings were subjected to immersion tests, and the water transport process was analyzed using the Langmuir diffusion model. Molecular dynamics simulations were employed to explore the transport mechanisms. Low‐field nuclear magnetic resonance (LF‐NMR) was employed to semi‐quantitatively evaluate the distribution state of water during each immersion stage. Gray relational analysis was used to evaluate the correlation of microstructural indicators with water transport parameters. The study found that water absorption increased rapidly within the first 48 h of immersion, then decreased, reaching saturation at 336 h. Water within the coatings existed primarily as bound water at all stages. The Langmuir model effectively describes the dynamic diffusion of free and bound water phases, with results showing high consistency with LF‐NMR data. Water diffusion rates and distribution states are synergistically regulated by the coupling of polar functional groups and microscopic pores. Notably, within the scope of the formulations tested, polar functional groups show a stronger statistical correlation with diffusion behavior than microscopic pores.