Hydrophobic deep eutectic solvent‐based ionic conductive gels with highly stretchable, fatigue‐resistant and adhesive performances for reliable flexible strain sensors

Abstract

Owing to the advantages of temperature resistance, low cost, and biocompatibility, deep eutectic solvent (DES)‐based ionic conductive gels have attracted increasing research interest for flexible devices in recent years. However, current DES gels are all based on hydrophilic DES, which tend to absorb a large amount of environmental moisture, resulting in gel softening and adversely affecting the durability of the device. In this work, we highlight for the first time that N,N‐dimethylacrylamide monomer, and the obtained polymer can form hydrogen‐bonding networks with hydrophobic DES, methyl trioctyl ammonium chloride/ethyl 4‐hydroxybenzoate (1:2), thereby obtaining a hydrophobic DES‐based gel through photo‐polymerization. The resultant DES gel displays high stretchability (~900%), toughness (341.14 kJ m−3), anti‐fatigue property (recovery after 500 compression cycles), desirable conductivity (0.12 mS cm−1), adhesiveness and high transparency (>90% visible light transmittance). Notably, the hydrophobic DES‐based gel absorbs only 2 wt% water but exhibits significant water‐induced stiffening after exposing in ambient air for 1 week. These properties lead to the successful realization of the DES gels as wearable sensors to precisely monitor human motion. This work may open new avenues for the development of hydrophobic DES‐based gel ionotronics with functional performance.

Deep eutectic solvents towards green polymeric materials

“…6b). 119 Here, the traditional ChCl was not used as the HBA to facilitate the conductivity, instead methyltrioctylammonium chloride : ethyl 4-hydroxybenzoate (1 : 2) was chosen to enhance the hydrophobicity. A stretchability of 900%, toughness of 341.14 kJ m −3 , and tensile strength of 97.58 kPa were achieved owing to the reversible hydrogen-bond interactions between the DES and the polymer in the gel with 30 wt% polymer scaffolds.…”

Tough and Stretchable Phenolic‐Reinforced Double Network Deep Eutectic Solvent gels for Multifunctional Sensors with Environmental Adaptability

“…[12] The responsiveness to external forces makes DES gels promising as flexible sensors for human movement and health assessment. [13,14] For example, researchers have prepared a wearable strain sensor by poly(N-hydroxyethylacrylamide) (PHEAA) in choline chloride-ethylene glycol (ChCl-EG) DES to detect large and microscopic movements. [15] Similarly, the researchers used (R)-12-hydroxystearic acid hydrazide (HSAH) co-assembled with PHEAA in various DES to prepare low molecular weight super polymer double network (SP-DN) gels for application in wearable self-adhesive strain sensors.…”

Extremely Tough and Stretchable Hydrophobic Deep Eutectic Solvent-Based Gels with Strong Adhesion and Moisture Resistance for Wearable Strain Sensors

“…While these hydrophobic DES-based gels exhibited high stretchability, they lacked mechanical strength, toughness, and adhesive properties, restricting their practical applications. 35 To address these limitations, we aim to develop hydrophobic DES gels with exceptional toughness, high stretchability, strong adhesion, self-healing, and self-recovery properties.…”

“…However, hydrophilic DESs are sensitive to moisture, affecting the mechanical and electrical properties of resulting gels, as well as their adhesive properties. − Hydrophobic DES, on the other hand, offers stability in moist environments, − but there are limited reports on polymeric DES gels incorporating hydrophobic DES, especially those with conductive properties. − Our previous research developed ionic conductive gels by in situ photopolymerization of dimethylacrylamide in a hydrophobic DES, methyltrioctylammonium chloride/ethyl 4-hydroxybenzoate. While these hydrophobic DES-based gels exhibited high stretchability, they lacked mechanical strength, toughness, and adhesive properties, restricting their practical applications . To address these limitations, we aim to develop hydrophobic DES gels with exceptional toughness, high stretchability, strong adhesion, self-healing, and self-recovery properties.…”