Strong Tough Poly Acrylic‐co‐acrylamide Hydrogels via a Synergistic Effect of Fiber and Metal‐Ligand Bonds as Flexible Strain Sensors

Abstract

Developing conductive hydrogel‐incorporated strain sensors with high gauge factor (GF) and toughness for wearable applications is challenging. Herein, a facile strategy to fabricate strong, tough polyacrylamide‐co‐acrylic acid [P(AAm‐co‐AAc)] hydrogels via the synergy of fiber and metal‐ligand bonds is proposed. Through the secondary equilibrium approach, the pristine P(AAm‐co‐AAc) gel network is reconstructed with fiber and carboxyl–Zr4+ (Zirconium ion) coordination bonds intertwined over the entire gel matrix, generating a synergistic reinforcement in mechanical properties. The resultant hydrogels display a maximum tensile strength of 8.50 MPa and a fracture energy of 2.75 kJ m−2, which is 1–2 orders of magnitude greater than the original P(AAm‐co‐AAc) gels. It is also experimentally approved that by selecting different natural fibers, multivalent metal ions, and synthetic macromolecules containing carboxyl groups, the proposed approach is effective and can be generalized to fabricate strong, tough gels. Additionally, the electrical properties of obtained gel are evaluated by fabricating it into a stretchable strain sensor for object identification or human motion detection. The results reveal a high GF of 5.07 under a strain smaller 55%. These hydrogels are expected to enable numerous applications in soft robotics or wearable healthcare.

A responsive supramolecular hydrogel with robust mechanical properties for actuator and strain sensor

“…The peak of 532.1 eV was assigned to C-O-Zr (20.55 at%), proving the formation of carboxyl-Zr 4+ coordination bonds. 21 The two peaks with bending energies of 182.8 eV and 185.3 eV in the deconvoluted Zr3d orbit spectrum were belonging to Zr3d 5/2 and Zr3d 3/2 (Figure 2d), 21,23,28 respectively. The XPS analysis of the PAA-Zr 4+ hydrogel also obtained similar O1s and Zr3d orbital spectra (Supporting Information S2 b, c).…”

Tough Ion-Conductive Hydrogel with Anti-Dehydration as a Stretchable Strain Sensor for Gesture Recognition

“…Recent advancements in the development of ion-conductive hydrogels have predominantly relied on the incorporation of salt ions directly into the networks. Unfortunately, these hydrogels are prone to dehydration, which restricts their practical utilizations. − Except for its excellent anti-dehydration discussed above, the DRY-PA-Fe 3+ gel demonstrated an increased conductivity of 3.25 S m –1 , compared to that of 1.12 S m –1 of the ASP-PA gel (Figure S11). This enhancement could be attributed to a large number of positive or negative free ions in the network for DRY-PA-Fe 3+ gels.…”

Polymer Complex Fiber: Property, Functionality, and Applications

“…In addition, the brittle and stiff PCFs can gain elasticity by addition of a low glass transition temperature polymer during the fabrication. For example, the ALG/Ca fiber exhibited ultralow elongation because of the rigid structure of ALG and the “egg-box” structure of ALG/Ca complexes, and its elastic property can be improved using polyacrylamide as an additive. − Wu et al fabricated a high-performance ALG/Ca/polyacrylamide fiber with ultrastretchability. The incorporated polyacrylamide not only contributed to the high elasticity but also endowed the fiber with a double network and introduced effective energy dissipation, leading to a 1400% elongation of the fiber without breaking …”