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

Abstract

which could be conveniently constructed according to a model designed in advance.Macromolecular crosslinking hydrogel [15] and double-network hydrogel [16] fabricated by introducing the energy dissipation mechanism exhibit distinguished comprehensive mechanical properties: high strength, large strain, and high toughness. [16] The toughness is attributed to the cooperation of the crack bridging of chemical crosslinking with the unzipping of physical network based on hydrogen bonds. [17] Crack bridging of chemical crosslinking results in a ductile network, and physical crosslinking forms a reversible brittle network. [17,18] When the gel is stretched, the chemical crosslink bonds remain intact, while the hydrogen bonds break and dissipate energy. The hydrogen bonds could recover during a definite time interval after removing the stress. Recently, Zhu et al. have reported a stretchable and tough hydrogel synthesized by incorporating two types of crosslinking interactions. [19] A radical polymerization of acrylic acid (AA) was triggered by visible light radiating, curling carboxymethyl cellulose (CMC) was exploited as a crosslinker and co-initiator. Herein, we employed the facile, one-pot, visible-light-triggered poly merization to re-engineer a double crosslinked network of polyacrylic acid (PAA; denoted as PAA-CMC@KCl ionic gel, containing 1.2903 mol L −1 KCl), exploiting CMC as a crosslinker and KCl as a conductive ion donor. In which, the hydrogen bond and the micro-aggregates of CMC chains were applied to form the secondary crosslinking, endowing the ionic gel with an efficient energy dissipation structure. Figure 1A shows that a strip of PAA-CMC@KCl ionic gel with a width of 4.30 mm and a thickness of 1.85 mm can lift up and shift a steel block with a weight of 1.5 kg without failure, indicating its excellent mechanical performance. Figure 1B is the typical stress-stretch curve of PAA-CMC@KCl ionic gel. It is found that the tensile strength reaches 1.33 MPa, the rupture strain is 816.4%, and the toughness calculated from the area under the stress-strain curve [8] is 5.11 MJ m −3 . These mechanical performances are comparable with that of the hydroxypropyl cellulose/polyvinyl alcohol composite hydrogel, [20] and higher than that of the hydrogel (PAA/CMC) without KCl (fracture strength was 850 kPa, elongation at break was 700%). [19] This improvement may be attributed to the denser hydrogen bond among polymers due to the addition of mineral salt, Strain SensorsA 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...

Visible-Light Transparent, Ultrastretchable, and Self-Healable Semicrystalline Fluorinated Ionogels for Underwater Strain Sensing

“…The X-ray diffraction (XRD) patterns of PAA–PEO–ILs and SFIG showed a remarkable diffraction peak of 2θ at ∼20° (Figure e), which belongs to the crystalline domain of C–O–C segments from PEO. , For the SFIG samples, there is only a single typical and wide diffraction peak, indicating that there is no obvious phase separation within the PEO, P­(AA- co -HFBA), and [BMIM]­[BF 4 ] . Besides, the calculated crystallinity of SFIG (4.8%) is much lower than that of PAA–PEO–ILs (15.9%).…”

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

“…Visible light is a safe, low cost, and easily acquired trigger that has attracted attention in synthesis of polymers via radical-initiated polymerization in recent years [ 22 , 23 ]. Figure 1 presents the preparation process and interactions of the CDN-gel.…”

Advances in Materials for Soft Stretchable Conductors and Their Behavior under Mechanical Deformation

“…Ionic conductors are not confined to hydrogels and can also be formed as ionogels—ionic liquid-based gel systems—and also elastomers that include ions or ionic liquids. Ionogels are a new class of soft materials with ionic conductivity and thermal stability, and unlike most hydrogels, do not dry out in open air, offering a promising option for soft stretchable conductors [ 13 , 120 , 128 , 129 , 130 , 131 , 132 ]. Figure 5 depicts examples of transparent ionogels ( Figure 5 a,b) along with a representative demonstration of mechanical strain ( Figure 5 b).…”