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

Deep eutectic solvent (DES) gels show significant potential for flexible device applications due to their advantageous properties, including excellent ionic conductivity, stability, biocompatibility, and cost-effectiveness. However, hydrophilic DES gels face challenges related to their mechanical strength, adhesion, and moisture sensitivity. In this study, we exploited a moderate polarity mismatch between PMAA and a hydrophobic DES, formed from methyltrioctylammonium chloride and ethylene glycol (1:2), to enhance interpolymer hydrogen bonding through solvent effects. This approach successfully produced highly stretchable, transparent, strongly adhesive (8.05 MPa), and extremely tough hydrophobic DES gels (toughness 11.50 MJ m–3 at 30 wt % polymer content) through the in situ polymerization of methacrylic acid within the hydrophobic DES. These gels also exhibited remarkable self-recovery (96%) and self-healing capabilities due to abundant noncovalent hydrogen bonding interactions within the polymer network. Furthermore, these DES gels displayed outstanding ionic conductivity (0.69 mS cm–1 at room temperature) and sensing capabilities, making them suitable as strain sensors to detect human motion. They also demonstrated excellent freeze resistance, thermal stability, and superior moisture resistance. The strategies to suppress microphase separation caused by excessive hydrogen bonding self-interaction between polymers to produce stiff and tough hydrophobic DES gels at a high polymer content were also proposed. This study introduces an innovative approach to develop robust DES gels with tailored functionality by leveraging solvent effects to fine-tune the gel network structure.