Simple and Rapid Way to a Multifunctionally Conductive Hydrogel for Wearable Strain Sensors

Abstract

Conductive hydrogels have gained increasing attention in the field of wearable smart devices. However, it remains a big challenge to develop a multifunctionally conductive hydrogel in a rapid and facile way. Herein, a conductive tannic acid–iron/poly (acrylic acid) hydrogel was synthesized within 30 s at ambient temperature by the tannic acid–iron (TA@Fe3+)-mediated dynamic catalytic system. The TA@Fe3+ dynamic redox autocatalytic pair could efficiently activate the ammonium persulfate to initiate the free-radical polymerization, allowing the gelation to occur easily and rapidly. The resulting hydrogel exhibited enhanced stretchability (3560%), conductivity (33.58 S/m), and strain sensitivity (gauge factor = 2.11). When damaged, it could be self-healed through the dynamic and reversible coordination bonds between the Fe3+ and COO– groups in the hydrogel network. Interestingly, the resulting hydrogel could act as a strain sensor to monitor various human motions including the huge movement of deformations (knuckle, wrist) and subtle motions (smiling, breathing) in real time due to its enhanced self-adhesion, good conductivity, and improved strain sensitivity. Also, the obtained hydrogel exhibited efficient electromagnetic interference (EMI) shielding performance with an EMI shielding effectiveness value of 24.5 dB in the X-band (8.2–12.4 GHz). Additionally, it displayed antibacterial properties, with the help of the activity of TA.

Janus Hydrogel with Both Sticky Adhesion and Slippery Antifouling Properties for Strain Sensing

“…The voltage was set to 0.05 V. The conductivity of the TA@ PVA/PSBMA hydrogel was calculated as follows: σ = L × 100/( R × A ), where L is the distance between probes (cm), R is the resistance of hydrogel (Ω), and A is the cross-sectional area (cm 2 ) in the vertical current direction. In addition, the relative resistance was calculated as follows: Δ R / R 0 (%) = 100 × ( R – R 0 )/ R 0 , where R is the resistance of the hydrogel and R 0 is the resistance of the hydrogel after strain is applied …”

“…In addition, the relative resistance was calculated as follows: ΔR/R 0 (%) = 100 × (R − R 0 )/ R 0 , where R is the resistance of the hydrogel and R 0 is the resistance of the hydrogel after strain is applied. 27 Characterizations. The values of the contact angle (CA) and sliding angle (SA) were measured by a Kruss DSA 100 (Kruss Company, Ltd.) device at room temperature.…”

Transparent and Environmentally Adaptive Semi-interpenetrating Network Hydrogels for Electromagnetic Interference Shielding

“…Nowadays, the harm of electromagnetic waves (EMW) to human health and electronic equipment operation is increasing, and designing green EMI shielding materials with low reflectivity is the current trend. − As we know, after water is polarized, electromagnetic waves (EMW) in the GHz and THz bands could be dissipated or attenuated by water. − If enough water is loaded in a material with suitable conductivity, effective absorption of the incident electromagnetic waves could be achieved with low reflection . Hydrogels contain a large amount of water, which is supposed to be crucial in electromagnetic interference (EMI) shielding materials. − Hence, the preparation of hydrogels exhibiting exceptional electromagnetic shielding can guarantee the normal operation of soft electronics …”