Novel sea cucumber-inspired material based on stiff, strong yet tough elastomer with unique self-healing and recyclable functionalities

Abstract

Constructing ideal sea cucumber-inspired materials (SCIMs), which are able to transform to stiff yet tough materials after exposure to external stimuli, and better resist external impact, is a huge challenge. Herein, inspired by nature, abundant Zn²⁺–imidazole cross-links were distributed into a hydrogen-bonded/Diels–Alder dynamic covalent dual-crosslinked network, resulting in an extraordinary enhancement in mechanical properties and resulted in the synthesis of a stiff, strong yet tough SCIM, which demonstrates excellent impact-resistant characteristics under dry conditions. Taking advantage of the reversible destruction/reformation of its noncovalent cross-links that are influenced by humidity, the SCIM switches from being soft/weak to stiff/tough upon regulation of humidity. The experimental results show that the extent of the soft-stiff switching ability (E_max/E_min) is high, up to ≈107.6 MPa. The stiff SCIM (E ≈ 183 MPa) was able to autonomously restore its mechanical properties during the dry–wet cycle and the healing efficiency was as high as 85.5%. Moreover, the surface scratches were also totally healed without leaving any minor scars. Thanks to the synergistic cooperation of dynamic DA covalent bonds, hydrogen bonds and coordination bonds, the SCIM can also be recycled.