A Review on the Thermo-Mechanical-Chemical Coupling Effects of Water in Different States on Polymer Coatings

Water, with its diverse physical states and strong environmental reactivity, plays a central role in accelerating the failure of polymer coatings. Among all environmental stressors, moisture-induced degradation is particularly detrimental to the long-term reliability of engineered systems, often significantly shortening service life. Polymeric coatings, composed of high-performance resins such as epoxy, polyurethane, or acrylics, are widely used in aerospace, marine, electronic, and structural applications due to their cost-effectiveness and multifunctional barrier properties. However, moisture ingress typically initiates at the coating surface and progressively migrates toward the polymer-substrate interface, inducing blistering, delamination, interfacial corrosion, and mechanical debonding. In addition to its widespread presence, water exhibits high chemical reactivity, capable of dissolving corrosive ions (e.g., O, CO, Cl), altering the thermomechanical behavior of coatings, and participating in hydrolytic chain scission. Furthermore, water rarely acts in isolation; its interaction with thermal, salt, ultraviolet, electric, or mechanical stressors results in complex multi-field coupling that accelerates failure processes.This review provides a comprehensive and structured analysis of the water-induced failure mechanisms in polymeric coatings under real-world environmental conditions. It categorizes water-driven degradation into three main domains: (1) chemical degradation due to water's polarity, hydrogen bonding, and reactivity; (2) mechanical damage from hydrostatic pressure, phase transitions, and impact loading; and (3) thermal deterioration linked to water's role as a heat carrier. The synergistic effects of water under high humidity, temperature cycling, and corrosive atmospheres are emphasized to establish a unified framework for understanding coating failure modes and improving system-level environmental adaptability.