Nanoclay-Enhanced Self-Healing of Polyurethane-Urea Coatings Enabled by Disulfide Exchange

Abstract

Functional materials that combine mechanical robustness with autonomous self-healing are highly desirable for coatings and structural materials operating in aqueous environments. Here we report amphiphilic polyurethane-urea (PUU) networks incorporating polyethylene glycol (PEG) and polydimethylsiloxane (PDMS) segments together with dynamic urea linkages and aromatic disulfide bonds introduced via 4,4'-diaminodiphenyl disulfide (DPDS), further reinforced with amine-functionalized montmorillonite nanoclay. Density functional theory calculations establish the energetic hierarchy of the relevant dynamic bond reactions in vacuum and water, indicating that urea-related and disulfide pathways are kinetically accessible under moderate conditions, whereas urethane exchange is substantially less favorable. Guided by these insights, PUU networks and nanoclay composites were synthesized and characterized structurally and mechanically. The nanoclay was well dispersed within the amphiphilic matrix and significantly increased the storage modulus of the materials. Remarkably, incorporation of amine-functionalized nanoclay accelerated healing kinetics despite substantially increasing the modulus of the network, mitigating the conventional trade-off between stiffness and self-healing. Tensile healing experiments showed that nanoclay-reinforced PUU-DPDS networks achieved nearly complete mechanical recovery, with toughness reaching 94% in air and 81% under water after 24 h. At elevated temperature, the strength recovered to about 90% after 8 h at 60 °C. These results demonstrate that reactive nanoclay nanoparticles can simultaneously reinforce polyurethane-urea networks and promote dynamic bond exchange, enabling mechanically robust coatings with efficient self-repair in both dry and aqueous environments.