Novel hydrophobic self-healing urushiol-PDMS/MWCNT composite coatings: Experimental and molecular dynamics investigations

Abstract

Easy-clean polymer coatings with self-healing capabilities exhibit significant industrial relevance, yet achieving a balance between exceptional self-healing performance and mechanical robustness remains a challenge. In this study, a furan-functionalized urushiol derivative (urushiol-FA) was synthesized using natural urushiol as the starting material. To enhance chain mobility and impart inherent hydrophobicity, flexible poly (dimethylsiloxane) (PDMS) segments were integrated into the bis-maleimide (BMI) framework. Subsequently, a self-healing urushiol-based coating was developed by reversible crosslinking of urushiol-FA with PDMS-BMI via Diels-Alder cycloaddition. To further improve mechanical robustness, multi-walled carbon nanotubes (MWCNTs) were uniformly dispersed within the polymer network as reinforcing components. The surface properties, including surface energy, binding energy, and water contact angle (WCA) were preliminarily evaluated through molecular dynamics (MD) simulation. Subsequent experimental analyses of filler dispersion and WCA demonstrated excellent agreement with computational predictions. Despite a reduction in hydrophobicity resulting from elevated surface energy and non-bonded interactions with water molecules upon MWCNT incorporation, the composite coating containing 2.5 wt% MWCNT still achieved a WCA of 121.6°, attributed to increased surface roughness. Furthermore, MWCNT integration improved the thermal stability, self-healing efficiency, and mechanical properties of the coating. Notably, the composite coatings displayed effective healing performance at both moderate temperature (120 °C) and low temperature (60 °C). After three consecutive damage-healing cycles, the composite coating with 1.5 wt% MWCNT still maintained a healing efficiency of 93.42 % at 60 °C. The facile fabrication process and synergistic performance of the urushiol-PDMS/MWCNT composite coatings highlight their promising applicability in advanced self-healing and easy-clean protective systems.