A Universal Interfacial Strategy Imparting Hydrophobicity to Hydrophilic Eutectogels for Robust Adaptation to Extreme Aqueous Environments

Eutectogels and DES-based elastomers offer eco-friendly, cost-effective solutions for wearable devices but face limitations in underwater applications due to their high hygroscopicity. In this study, we present a strategy for developing a core–shell elastomer (CSE) based on deep eutectic solvents (DESs) that remains stable and functions effectively underwater. The hydrophobic shell (HS) is composed of a natural DES of thymol and camphor, while the printable conductive core (CC) is based on a polymerizable DES of acrylic acid and choline chloride. By employing an interfacial polymerization approach, the core–shell interface is reinforced with strong covalent bonds rather than weak physical interactions, enhancing the structural integrity. The CSE demonstrates excellent mechanical properties, including a tensile strength of 548 kPa and a stretchability of up to 680% strain. Additionally, it exhibits hydrophobicity with a water contact angle of 91° and remains stable underwater and in harsh environments such as pH 1, pH 14, and saline water. As a result, the CSE serves as a reliable underwater strain sensor and enables Morse code communication. Furthermore, with the printability of CC, various structures can be fabricated, expanding its potential for developing advanced core–shell materials for underwater applications.