Hierarchically Structured Stretchable Conductive Hydrogels for High-Performance Wearable Strain Sensors and Supercapacitors

Abstract

A strategy of creating stretchable conducting hydrogels for emerging soft electronics is reported. With ice-templated low-temperature polymerization (ITLP), the conducting gel exhibited a hierarchical dendritic microstructure with mitigated nanoaggregation and significantly enhanced electrical conductivity and toughness. Using such gels, strain sensors presented a broad sensing range and high sensitivity for health monitoring. Stretchable solid-state supercapacitors demonstrated remarkable capacitance and flexibility as wearable energy-storage devices. Such a general ITLP method may create diverse soft-electronic materials for energy, healthcare, and robotic applications.

Hydrogels and Their Role in Biosensing Applications

“…The applications of wearable devices range from the detection of human movements to force sensing to detection of small molecules. [117][118][119][120] For example, a wearable device on skin, a flexible silk fibroin patch with encapsulated enzyme served as substrate for a conducting polymer, which was photocrosslinked on top. This flexible and biodegradable skin like patch served as a free-standing electronic device.…”

Tough‐Hydrogel Reinforced Low‐Tortuosity Conductive Networks for Stretchable and High‐Performance Supercapacitors

“…[ 15,16 ] The nonconductive elastic hydrogel scaffolds are often functionalized with conducting polymers like polypyrrole, polyaniline, poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), and graphene for electrical conductivity, [ 17 ] using methods like infiltration by liquid‐/vapor‐phase and in situ polymerization. [ 18–27 ] However, the mass loading of conducting polymers by infiltration methods is relatively low (<10 mg cm −2 ), as monomers are barricaded by the semicontinuous pores to diffuse into the hydrogel. [ 18–22 ] Therefore, only thin hydrogel electrodes are best compatible with this method to gain sufficient conductivity and electroactive material.…”

“…[ 18–22 ] Therefore, only thin hydrogel electrodes are best compatible with this method to gain sufficient conductivity and electroactive material. The alternative in situ polymerization method can yield higher mass loadings; [ 23–27 ] however in particular cases, the solubility cap limits the maximum content of conducting polymers (e.g., pyrrole in water, PEDOT:PSS in water) in the aqueous solvent to stably coexist with the hydrogel monomers and the structure may vary significantly upon slight changes in the composition ratio. [ 23 ] “All‐conducting‐polymer” hydrogel electrodes have also been fabricated to show both flexibility and good conductivity.…”

“…[ 28–32 ] However, these polymers may face embrittlement under stretching (strain <10%) and direct polymerization of the less soluble conducting polymers produces stacked spherical aggregates with poor electrical interconnection. [ 27 ] Successful methods involve using 2D conducting fillers [ 31 ] that are intrinsically robust and do not aggregate into spheres, synthesizing 1D conducting polymer fibers using special crosslinkers [ 30 ] and adding plasticizer agents. [ 33 ]…”

Visualizing thermal distribution through hydrogel confined ionic system

“…However, the mixture of ionic liquid and solvent is hardly freestanding, making it scarcely possible to attach to the surface of an object ( Matsumoto and Endo, 2008 ; Gao et al., 2019 ; Wang, 2020 ; Zhou et al., 2019 ). An encapsulating container is essentially needed to confine the mixture of IL and solvent in a specific region which goes against rapid thermal transmission and also meets the leakage problem ( Chen et al., 2018 ; Yang et al., 2018b ; Lu et al., 2019 ; Zhao et al., 2020a , 2020b ).…”