Fabrication and mechanical behaviors of novel supramolecular/polymer hybrid double network hydrogels

Double network hydrogels (DN gels) are one of most extensively investigated high strength hydrogels. However, most of DN gels are concern to macromolecules, low-molecular-weight gelators (LMWG)-based supramolecular hydrogels are rarely reported to fabricate recoverable DN gels. Owing to the low mechanical properties, LMWG-based supramolecular hydrogels are hardly fabricated as conductive materials for human motion monitoring. Herein, we report a general strategy to fabricate strong, tough and conductive cholate-based supramolecular gels with double network (DN) structure (i.e. La-cholate/PAAm DN gels), consisting of La-cholate supramolecular gel as first network and covalent polyacrylamide gel (PAAm gel) as second network, in which La-cholate supramolecular gel was self-assembled by La3+ ions and sodium cholate under sonication via the synergistic effect of hydrogen bonds, hydrophobic interactions and metal-coordination. At optimal condition, La-cholate/PAAm DN gel exhibited high tensile properties (fracture stress of 0.314 MPa, fracture strain of 29.85 mm/mm, elastic modulus of 90 kPa, and work of extension of 5.678 MJ/m3) and high toughness (tearing energy of 1098 J/m2), which are comparable to conventional chemical or hybrid DN gels. Meanwhile, La-cholate/PAAm DN gel also showed rapid self-recovery property (stiffness recovery of 84% and toughness recovery of 46% after resting for 3 min) at room temperature and λ-dependent luminescent property under UV-light. More importantly, cholate-based supramolecular gels with DN structure could be prepared with various metal ions and monomers. Interestingly, our cholate-based DN gels were ionically conductive, which could be used as strain sensor to finely detect the human motions. We hope our design principles, along with the simple method and cholate-based DN gels, can be generally applied to develop a new generation of strong and tough LMWG-based supramolecular hydrogels with various functionalities.