Fatigue-resistant hydrogels controlled by sulfanilic acid cross-linker at molecular level

Most hydrogels (gels) suffer from fatigue under long-time loads, since these gels primarily pay attention to optimizing dissipated energy mechanisms but often ignore that whether topological structures is homogeneous or not. The stress concentrations in inhomogeneous topological networks will accelerate fatigue damage. Fatigue is considered as a molecular disease. Thus, we expected to endow gels with excellent anti-fatigue property beginning from cross-linker in the view of molecular engineering. Herein, sulfanilic acid (SA) was reported as high-functional cross-linker to improve mechanical performance of gels. On the one hand, SA with advantages of small molecule and water-soluble can overcome heterogeneity of cross-links in topological structures of gels; On the other hand, multiple hydrogen bonds can be established between SA and poly(acrylamide) (PAM) chains, endowing PAM/SA gel with distinct energy dissipation mode. Thereby, the deformed network of PAM/SA gel can re-construct efficiently after the release of loads. PAM/SA gel displayed a good self-recoverability (67% dissipate energy, 98% elastic modulus and 99% stretching stress recovery within 3 min), and a remarkable fatigue resistance even after 50 tensile loading-unloading cycles at 500% strain. This work opens a new horizon to develop fatigue-resistant gels at molecular level under the support of SA as novel cross-linker.