Molecular dynamics interpretation of hydrogen bonds for colorless, water-resistant, tough, and self-healable elastomers

Abstract

Transparent, self-healing elastomers play a vital role as protective coatings, particularly in display applications. However, mechanical toughness and efficient self-restoration are often mutually exclusive. A performance equilibrium can be achieved through the molecular design of reversible bonds. However, aromatic disulfide-based dynamic covalent bonds produce an unattractive coloration owing to electron chromophores. In addition, H-bond moieties induce unintended adhesion to the substrates and are limited by hydration-induced weakening. In this study, the molecular design of aliphatic disulfides is presented for colorless, non-tacky, and water-resistant elastomers that rapidly self-heal at ambient temperatures. By employing molecular dynamics simulations, we demonstrate that an excess of H-bond acceptors promotes shorter bond exchange durations while maintaining a higher quantity of cohesive H-bonds, surpassing the performance of equivalent donor/acceptor systems at identical donor concentrations. In addition, dynamic H-bond exchange enables effective healing, whereas the increased H-bond cross-linking density ensures both waterproofness and an impressive tensile strength of 45 MPa. Furthermore, the absence of aromatic groups grants the elastomers a remarkable transmittance of 99%. The optimized properties achieved in this study using the proposed strategic molecular designs will further the commercialization of self-healing thermoplastic polyurethanes as intelligent protective coatings.