Synergistic Hydrophobic and Hofmeister Effects Drive Recyclable, Tough, and Antiswelling Hydrogels for Underwater...

The development of high-performance hydrogels for underwater flexible electronics is hindered by a long-standing, seemingly irreconcilable trade-off among antiswelling capability, mechanical robustness, and recyclability. Here, we report a synergistic hydrophobic and Hofmeister effect (SHHE) strategy to fabricate recyclable, tough, and antiswelling hydrogels (RTASH). By incorporating salts (e.g., CO₃^2-, SO₄^2-) into a hydrophobically modified polymer network, RTASH achieves exceptional antiswelling performance (swelling ratio < 5% after 60 days), high toughness (fracture toughness: 1.9 MJ m^-3), and stable ionic conductivity (0.35 S m^-1). The dynamic physical cross-links enable full recyclability, with the material retaining over 80% of its mechanical strength after three reprocessing cycles. When applied as an underwater strain sensor, RTASH exhibits high sensitivity (GF = 0.6), fast response (0.3 s), and long-term stability over 60 days of continuous operation. Leveraging its tunable electromechanical properties, we demonstrate real-time Morse code communication underwater including the reliable transmission of SOS distress signals. This work presents a straightforward and sustainable material fabrication strategy to advance the development of environmentally adaptive underwater communication systems.