Bulk toughness and interfacial toughness (surface adhesive property) are the two highly desirable, but different properties of polymer hydrogels. Bulk toughness prevents hydrogel damage from highly mechanical deformation, while interfacial toughness enables strong adhesion of the gels on solid surfaces. However, conventional design wisdom prevents both bulk and interfacial toughness to be presented in the same hydrogel, because the bulk properties of hydrogels are usually different from the interfacial properties of the same hydrogels on solid surfaces. Here, we design and synthesize a fully physically-linked Agar (the 1st network)/poly(N-hydroxyethyl acrylamide) (pHEAA, the 2nd network) where both networks are physically crosslinked via hydrogen bonds. Bulk Agar/pHEAA hydrogels exhibit high mechanical properties (~2.6 MPa tensile stress, 8.0 tensile strain, ~8000 J/m2 tearing energy, ~1.62 MJ/m3 energy dissipation), high self-recovery without any external stimuli (~62%/30% toughness/stiffness recovery), and self-healing property. More impressively, without any surface modification, Agar/pHEAA hydrogels can be easily and physically anchored onto different non-porous solid substrates of glass, titanium, aluminum, and ceramics to produce super adhesive hydrogel-solid interfaces (i.e. high interfacial toughness of ~2000-7000 J/m2). Comparison of as-prepared and swollen gels in water and hydrogen-bond-breaking solvents reveals that strong bulk toughness provides a structural basis for strong interfacial toughness, and both high toughness mainly stem from cooperative hydrogen bonds between and within two networks and between two networks and solid substrates. This work demonstrates a new gel system to achieve super high bulk and interfacial toughness on non-porous solid surfaces.

Super bulk and interfacial toughness of fully physically-crosslinked double-network hydrogels

255th National Meeting (2018)

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