Cooperative Tridentate Hydrogen-Bonding Interactions Enable Strong Underwater Adhesion

Multidentate hydrogen-bonding interactions are a promisingstrategyto improve underwater adhesion. Molecular and macroscale experimentshave revealed an increase in underwater adhesion by incorporatingmultidentate H-bonding groups, but quantitatively relating the macroscaleadhesive strength to cooperative hydrogen-bonding interactions remainschallenging. Here, we investigate whether tridentate alcohol moietiesincorporated in a model epoxy act cooperatively to enhance adhesion.We first demonstrate that incorporation of tridentate alcohol moietiesleads to comparable adhesive strength with mica and aluminum in airand in water. We then show that the presence of tridentate groupsleads to energy release rates that increase with an increase in crackvelocity in air and in water, while materials lacking these groupsdo not display rate-dependent adhesion. We model the rate-dependentadhesion to estimate the activation energy of the interfacial bonds.Based on our data, we estimate the lifetime of these bonds to be between2 ms and 6 s, corresponding to an equilibrium activation energy between23k (B) T and 31k (B) T. These values are consistent withtridentate hydrogen bonding, suggesting that the three alcohol groupsin the Tris moiety bond cooperatively form a robust adhesive interactionunderwater.