Highly Stretchable and Transparent Double-Network Hydrogel Ionic Conductors as Flexible Thermal–Mechanical Dual Sensors and Electroluminescent Devices

Abstract

The latest generation flexible devices feature materials that are conductive, highly stretchable, and transparent to meet the requirements of a reliable performance. However, the existing conductors are mostly electronic conductors, which cannot satisfy these high-performance challenges. A robust hydrogel ionic conductor was rapidly fabricated with a facile one-pot approach by employing bioinspired agar with a physically cross-linked network, polyacrylamide (PAM) with a photoinitiated cross-linked network under appropriate UV intensity, and Li+ as conductive ions. The resulting Li+/agar/PAM ionic double-network hydrogels could be fabricated into various shapes through injection. The unique ionic hydrogel showed a remarkable stretchability with over 1600% extension, high tension/compression strength (0.22 MPa/3.5 MPa), and toughness (2.2 MJ/m3). Furthermore, it was demonstrated to possess dual sensory capabilities through the combination of both temperature and mechanical deformation. This hydrogel ionic conductor exhibited high stretching sensitivity with a gauge factor of 1.8 at strain 1100% and bending sensitivity in a broad angle range of 30–150°, respectively. Such highly optical transparency and elasticity endow the hydrogel-phosphor composites with promising luminescent properties. The multifunctional ionic hydrogel can be used as soft conductors for application in flexible devices such as ionic skin for wearable sensors and luminescence display.

Customization of Conductive Elastomer Based on PVA/PEI for Stretchable Sensors

“…The hydrogen bond networks in the hydrogel provide conductive pathways for ion transport (Li + and Cl − ). [31] (Figure 3a). So far, the PVA 2 PEI 1 -LiCl hydrogel fulfills most of the conditions for fabricating wearable sensors.…”

Highly Stretchable, Elastic, and Sensitive MXene-Based Hydrogel for Flexible Strain and Pressure Sensors

“…However, with limited degree of crosslinking and high viscosity, single-network hydrogels exhibit poor mechanical property and stability [ 8 , 9 ]. This problem can be effectively alleviated by introducing effective energy dissipation domains or constructing a double-network hydrogel [ 10 – 12 ]. Nevertheless, it is still challenging to combine good mechanical property with high sensing performance to design a highly stretchable and sensitive strain sensing hydrogel for wearable electronics.…”

One‐shot radical polymerization of vinyl monomers with different reactivity accompanying spontaneous delay of polymerization for the synthesis of double‐network hydrogels

“…Then, an AAm network is formed by UV irradiation. There are many other reports of one‐pot synthesis of DN gels combining such a network by chemical crosslinking and a network by physical crosslinking 25–29 …”