(552a) Cooperative Hydrogen Bonding in Underwater Adhesion

Developing resilient underwater adhesives can be challenging, especially if contact between interacting surfaces needs to be made in water. For example, epoxy polymeric adhesives have found a variety of uses due to their exceptional adhesive strength, toughness, and applicability to many types of substrates.¹ However, they suffer from a great reduction in adhesion when applied in wet environments, severely limiting their applications.² Previous work has compared the effect of various surface treatments on the adhesive strength of DGEBA epoxy adhesives to aluminum panels in dry and hot/wet conditions. Surfaces treated with the tris buffer (tris(hydroxymethyl)aminomethane) outperformed untreated and silane/DOPA treated surfaces in both dry and wet lap shear tests. Cooperative hydrogen bonding was hypothesized as the possible mechanism for enhanced adhesion.³

In this presentation we report on our experiments characterizing the contribution of cooperative hydrogen bonding on underwater adhesion. We characterized adhesion between oligomers modified with a trivalent hydrogen bond group (tris, or tris(hydroxymethyl)aminomethane) in their backbones. We found that underwater adhesion of these oligomer was comparable to adhesion in air. We hypothesize that the strong underwater adhesion is due to the presence of the tris group and that the underlying mechanism for the strong adhesion is cooperative hydrogen-bonding. To validate this hypothesis, we varied the detachment rate during the detachment of 100 nm oligomer from mica (or aluminum). Beyond adhesion measurements we also monitored the contact radius and crack velocity. By varying the rate of crack propagation during detachment the lifetime of interfacial bonds can be determined, allowing us to characterize the kinetics of adhesive bonds in situ. We then relate rate-dependent adhesion to a model⁴ for cooperative hydrogen bonding suggesting that through cooperation, polymer hydrogen bonds can compete with interfacial water to maintain adhesive interactions under water. Beyond demonstrating strong underwater adhesion, these results also provide a methodology to connect intermolecular interactions to macroscale surface forces measurements that can be extended to adhesives with different chemistry.

(1) Schmidt, R. G.; Bell, J. P. Epoxy Adhesion to Metals. In Epoxy Resins and Composites II; Dušek, K., Ed.; Springer-Verlag: Berlin/Heidelberg, 1986; Vol. 75, pp 33–71. https://doi.org/10.1007/BFb0017914.

(2) Kerr, C.; Macdonald, N. C.; Orman, S. Effect of Certain Hostile Environments on Adhesive Joints. Journal of Applied Chemistry 2007, 17 (3), 62–65. https://doi.org/10.1002/jctb.5010170301.

(3) Tran, N. T.; Flanagan, D. P.; Orlicki, J. A.; Lenhart, J. L.; Proctor, K. L.; Knorr, D. B. Polydopamine and Polydopamine–Silane Hybrid Surface Treatments in Structural Adhesive Applications. Langmuir 2018, 34 (4), 1274–1286. https://doi.org/10.1021/acs.langmuir.7b03178.

(4) Chaudhury, M. K. Rate-Dependent Fracture at Adhesive Interface. J. Phys. Chem. B 1999, 103 (31), 6562–6566. https://doi.org/10.1021/jp9906482.