General Strategy To Fabricate Strong and Tough Low-Molecular-Weight Gelator-Based Supramolecular Hydrogels with Double Network Structure

Abstract

Low-molecular-weight gelator (LMWG)-based supramolecular hydrogels, self-assembled by small molecules via noncovalent interactions, have recently attracted great attention due to their unique structure–property relationship and potential applications spanning from functional materials to biomedical devices. Unfortunately, many LMWG-based supramolecular hydrogels are mechanically weak and can not even be handled by conventional tensile and tearing tests. Here, we propose several design principles to fabricate new LMWG-based hydrogels with a true double-network structure (G4·K+/PDMAAm DN gels), consisting of the supramolecular self-assembly of guanosine, B(OH)3 and KOH as the first, physical G4·K+ network and the covalently cross-linked poly(N,N′-dimethyacrylamide) (PDMAAm) as the second, chemical network. Different from those LMWG-based supramolecular hydrogels, G4·K+/PDMAAm DN gels exhibit high tensile properties (elastic modulus = 0.307 MPa, tensile stress = 0.273 MPa, tensile strain = 17.62 mm/mm, and work of extension = 3.23 MJ/m3) and high toughness (tearing energies = 1640 J/m2). Meanwhile, the dynamic, noncovalent bonds in the G4·K+ network can reorganize and reform after being broken, resulting in rapid self-recovery property and excellent fatigue resistance. The stiffness/toughness of G4·K+/PDMAAm DN gels can be recovered by 65%/58% with 1 min resting at room temperature, and the recovery rates are further improved with the increase of temperatures and resting times. Interestingly, G4·K+/PDMAAm DN gels also exhibit UV-triggered luminescence due to the unique G4-quartet structure in the G4·K+ supramolecular first network. A new toughening mechanism is proposed to interpret the high strength and toughness of G4·K+/PDMAAm DN gels. We believe that our design principles, along with new G4·K+/PDMAAm DN gel system, will provide a new viewpoint for realizing the tough and strong LMWG-based gels.