Cooperative Multivalent Weak and Strong Interfacial Interactions Enhance the Adhesion of Mussel-Inspired Adhesives

Abstract

Inspired by the strong adhesion of mussel byssal threads to surfaces, the incorporation of 3,4-dihydroxyphenylalanine (DOPA) in polymer architecture has become a popular strategy to improve the adhesion of the polymers. There are numerous literature reports of this bioinspired method to improve the adhesion performance of polymers. However, the mechanism behind the success of DOPA-based adhesion continues to be a puzzle as decoupling the contribution of interfacial adhesion to the alteration in chemistry is experimentally challenging. Herein, we designed mussel-inspired elastomers with four different functionalities to test the importance of aromatic and hydroxyl groups in determining the adhesion performance. With a combination of adhesion measurements, surface-sensitive spectroscopy, and molecular dynamics simulations, we show that the aromatic groups form weak multivalent acid–base interactions with the surface hydroxyl groups on sapphire. Also, the interaction of both phenyl (weak acid–base interaction) and −OH groups (strong acid–base interaction) of DOPA with sapphire −OH groups increases the adhesion of DOPA-based polymers compared to polymer analogs functionalized with either phenylalanine (only aromatic), serine (only hydroxyl), or tyrosine (aromatic and one hydroxyl) groups. Thus, this study illustrates the importance of both strong and weak acid–base interactions in enhancing adhesion.