Abstract
Self-healing polymer coatings are increasingly explored as a strategy to extend the service life of materials exposed to fluctuating environmental conditions. However, achieving reliable healing without compromising mechanical stability remains a significant challenge. In moisture-activated systems, the benefits of dynamic bond exchange must be balanced against the risk of humidity-driven softening and degradation. In this work, we first investigate how environmental factors govern autonomous healing by examining the interplay between temperature, humidity, and chain mobility in boronic ester–based epoxy coatings under realistic ambient conditions. Healing behaviour was assessed under four representative environments (i.35 °C/85 % RH, ii.35 °C/50 % RH, iii.25 °C/85 % RH, and iv.25 °C/50 % RH) using quantitative scratch recovery, supported by mechanical, thermal, and moisture-response characterisation. The results show that healing efficiency is governed by the cooperative action of temperature and humidity: elevated humidity facilitates bond exchange, while increased temperature enhances molecular mobility. When the glass transition temperature approaches or exceeds the service temperature, humidity partially compensates for restricted chain motion, enabling healing even under limited mobility.
To address material deterioration observed under prolonged humidity exposure, a second set of networks was designed incorporating both dynamic and static crosslinks to balance healing capability with structural stability. These hybrid networks exhibited rapid humidity-assisted healing while retaining load-bearing capacity and suppressing moisture-induced plasticisation, in contrast to highly dynamic systems. Overall, this study demonstrates that effective self-healing under realistic environmental conditions requires not only responsive dynamic bonds but also deliberate control of network architecture to mitigate long-term moisture damage. The findings provide practical design guidance for developing durable self-healing epoxy coatings suited for real-world service environments.
Keywords: Self-healing, epoxy coatings, boronic ester, dynamic covalent bonds, ambient environmental conditions.