Simultaneously toughening and stiffening elastomers with octuple hydrogen bonding

Abstract

Current synthetic elastomers suffer from the well-known trade-off between toughness and stiffness. By a combination of multi-scale experiments and atomistic simulations, we demonstrate a transparent unfilled elastomer with simultaneously enhanced toughness and stiffness. The designed elastomer comprises homogeneous networks with ultra-strong, reversible, and sacrificial octuple hydrogen bonds which evenly distribute the stress to each polymer chain during loading, thus enhancing stretchability and delaying fracture. Strong hydrogen bonds and corresponding nanodomains enhance the stiffness by restricting the network mobility, and at the same time improve the toughness by dissipating energy during the transformation between different configurations. In addition, the stiffness mismatch between hard hydrogen bonding domains and the soft polydimethylsiloxane-rich phase promotes the crack deflection and branching, which can further dissipate energy and alleviate local stress. These cooperative mechanisms endow the elastomer with both high fracture toughness (17016 J/m2) and high Young’s modulus (14.7 MPa), circumventing the trade-off between toughness and stiffness. This work is expected to impact many fields of engineering requiring elastomers with unprecedented mechanical performance.