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Carbon chains immobilize water molecules, making a hydrogel elastic across temperatures 

Abstract While in-situ underwater adhesives are highly desirable for marine exploration and underwater robotics, existing underwater adhesives suffer from significantly reduced performance compared to air-cured adhesives, mainly due to difficulties in removing interfacial water molecules. Here, we develop a pressure-sensitive in-situ underwater adhesive featuring superabsorbent particles infused with functional silane and hydrogel precursors. When injected into an underwater crack, the particles quickly absorb water, swell, and fill the crack. Mechanical pressure is applied to improve particle-particle and particle-substrate interactions, while heat is utilized to trigger thermal polymerization of the hydrogel precursors. This process creates porous adhesives via bulk polymerization and forms covalent bonding with the substrate via surface silanization. Our experiments demonstrate that mechanical pressure significantly enhances the adhesive’s stretchability (from 3 to 5), stiffness (from 37 kPa to 78 kPa), fracture toughness (from 1 kJ/m²to 7 kJ/m²), and interfacial toughness with glass substrates (from 45 J/m²to 270 J/m²). 

We report a mechano-diffusion mechanism that harnesses mechanical deformation to control particle diffusion in stretchable hydrogels with a significantly enlarged tuning ratio and highly expanded tuning freedom. 

Elastocaloric polymers, whose performance typically relies on phase transformation between amorphous chains and crystalline domains, offer a promising alternative to traditional refrigeration technologies. While engineering polymer‐network architecture has shown the potential to boost elastocaloric performance, the role of topological defects remains unexplored despite their prevalence in real polymers. This study reports a defect‐engineering approach in end‐linked star polymers (ELSPs) that enables an adiabatic temperature change of up to 8.14 ± 1.76 °C at an ambient temperature above 65 °C, showing an enhancement of 39% compared to ELSPs with negligible defects. This defect‐regulated solid‐state cooling is attributed to two competing effects of dangling‐chain defects on strain‐induced crystallization (SIC) and temperature‐induced crystallization (TIC), synergistically regulating the adiabatic temperature change. Specifically, increasing dangling‐chain defects monotonically lowers ELSPs’ mechanical performance at high temperatures due to suppressed SIC, but nonmonotonically impacts the mechanical performance at low temperatures due to the competition between suppressed SIC and enhanced TIC.