Researchers Achieve Strong Adhesion Underwater

Researchers Achieve Strong Underwater Adhesion An interfacial water layer prevents the formation of interfacial contacts and intermolecular interactions between the adhesive and substrate, so in nearly all underwater adhesion cases, water molecules typically act as a disruptive agent, resulting in weak bonding. For this reason, removal of interfacial water from substrate surfaces is necessary for the formation of super-strong underwater adhesion. Despite various singular physical interventions such as absorption, hydrophobic repulsion and extrusion, complete elimination of the interfacial water contradiction is difficult due to the inevitable presence of bound water at the interface. Therefore, conceptually novel material design in physical-chemical bonding and a multiscale approach with an unconventional dehydration mechanism are required for deep removal of water at the contact interface and self-adaptive cohesion enhancement to create strong underwater adhesives. In a study published in PNAS, a group led by Zhou Feng from the Lanzhou Institute of Chemical Physics (LICP) of the Chinese Academy of Sciences developed a self-strengthening liquid underwater adhesive (SLU adhesive) and achieved rapid and robust underwater bonding through deep water removal at the contact interface and self-adaptive cohesion development. To develop the SLU adhesive, researchers employed a multiscale dehydration mechanism based on physical-chemical bonding. The adhesion mechanism for interfacial water removal comprises three steps of multiscale dehydration: physical displacement of surface water on the substrate at the mm scale by SLU adhesive due to superior wettability, physical removal of water at the μm scale by generation of carbon dioxide bubbles from the chemical reaction between isocyanate groups and water at the interface, and simultaneous chemical consumption of surface-bound water at the molecular scale.   Academic Reference: Chenxi Qin et al, Water-assisted strong underwater adhesion via interfacial water removal and self-adaptive gelation, Proceedings of the National Academy of Sciences (2023). DOI: 10.1073/pnas.2301364120   Source