Hydrophobic association and ionic coordination dual crossed‐linked conductive hydrogels with self‐adhesive and self‐healing virtues for conformal strain sensors

Abstract

As a promising functional material, conductive hydrogel has attracted extensive attention, especially in flexible sensor field. Despite the recent developments, current hydrogels still experience several issues, such as limited stretchability, lack of self‐recovery and self‐healing capability, and insufficient self‐adhesion. Herein, dual cross‐linked (DC) poly (AA‐co‐LMA)SDS/Fe3+ hydrogels are fabricated subtly on the basis of ionic coordination interactions and the poly (AA‐co‐LMA)SDS hydrophobic association networks, which may provide one plausible routine to compensate the mentioned drawback of hydrogels. The hydrophobic association and ionic coordination networks work synergistically to endow the hydrogels remarkable stretchability (>1200%), high‐fracture strength (≈ 820 kPa), and excellent self‐healing capability. In addition, the DC hydrogel‐based strain sensors displayed a broad sensing range (0 ∼ 900%), conspicuous sensitivity (strain 0% ∼ 200%, gauge factor = 0.53; strain 200% ∼ 500%, gauge factor = 1.23; strain 500% ∼ 900%, gauge factor = 2.09), and pronounced durability. What's more, the self‐adhesive feature ensures the strain sensor always forming a good conformal contact with the skin during human movements and displaying remarkable bidirectional detection capability.

Tough, Anti-Swelling Supramolecular Hydrogels Mediated by Surfactant–Polymer Interactions for Underwater Sensors

“…Hence, the PAA gel seriously deformed after soaking in deionized water for 30 min. The P­(AA- co -LMA) SDS hydrogel also swelled rapidly in deionized water, and the swelling ratio reached 25 times after soaking for 24 h. The hydrophobic interactions between LMA hydrophobic sequences with the SDS alkyl tails can serve as cross-linking sites, which prevent the P­(AA- co -LMA) SDS hydrogel from dissolving in water . Compared with the P­(AA- co -LMA) SDS hydrogel, there is another important interaction in the P­(AA- co -LMA) CTAB hydrogel, that is, the electrostatic interaction between the N + of CTAB with the COO – on polymer chains.…”

“…The polymerization process of the P­(AA- co -LMA) CTAB hydrogel was recorded by attenuated total reflection accessory (ATR-FTIR) according to ref . The hydrogels were also tested with ATR-FTIR after 7 and 30 days of immersion in deionized water.…”

“…All the tensile property tests and cyclic tensile tests were performed according to the procedure described in ref .…”

“…Lap-shear adhesion tests of the hydrogels to various adhesion substrates were performed following the procedure described in ref . The method for sample preparation is illustrated in Figure S1, Supporting Information.…”

“…The ionic conductivity of the P­(AA- co -LMA) CTAB hydrogel and the sensing properties of the hydrogel-based sensor were investigated following the procedure described in ref . For the underwater sensing measurements, copper wires immersed in water were all tightly sealed with a waterproof tape to avoid short circuit.…”