Strain-Sensitive Performance of a Tough and Ink-Writable Polyacrylic Acid Ionic Gel Crosslinked by Carboxymethyl Cellulose.

A tough polyacrylic acid ionic gel is obtained using carboxymethyl cellulose as a crosslinker and KCl as a conductive ions donor. The polymerization process is initiated by ceric ammonium nitrate and triggered by visible light, which can be employed as a facile 3D printing process to fabricate arbitrary gel architectures. Curling macromolecular crosslinker and plentiful hydrogen bonds among polymers endow the ionic gel with superior mechanical performance including high tensile strength (≈1.33 MPa), large elongation (>8 times), high toughness (≈5.11 MJ m-3 ), and good self-recovery property. Importantly, the ionic gel can be assembled into a flexible strain sensor to precisely monitor the diverse human body motions in real time, that is, joints bending and muscle contraction, by recording the capacitance variation. This strain-sensitive performance, which can recover even after 1000 successive cycles, should enable the detection of body action and provide a potential application in health-care monitoring or human-computer user interfaces.

Multi-Sacrificial Bonds Enhanced Double Network Hydrogel with High Toughness, Resilience, Damping, and Notch-Insensitivity.

The engineering applications of hydrogels are generally limited by the common problem of their softness and brittlness. In this study, a composite double network ionic hydrogel (CDN-gel) was obtained by the facile visible light triggered polymerization of acrylic acid (AA), polyvinyl alcohol (PVA), and hydrolyzed triethoxyvinylsilane (TEVS) and subsequent salt impregnation. The resulting CDN-gels exhibited high toughness, recovery ability, and notch-insensitivity. The tensile strength, fracture elongation, Young's modulus, and toughness of the CDN-gels reached up to ~21 MPa, ~700%, ~3.5 MPa, and ~48 M/m3, respectively. The residual strain at a strain of 200% was only ~25% after stretch-release of 1000 cycles. These properties will enable greater application of these hydrogel materials, especially for the fatigue resistance of tough hydrogels, as well as broaden their applications in damping.