Changing polymer catechol content to generate adhesives for high versus low energy surfaces

Adhesive bonding is commonly used to replace mechanical fasteners in many applications. However, the surface chemistry of different substrates varies, making adhesion to a variety of materials difficult. Many biological adhesives are adept at sticking to multiple surfaces with a range of surface chemistries. Marine mussels utilize a catechol moiety within their adhesive proteins to bring about surface binding as well as cohesive cross-linking. Mimicking this functionality in synthetic polymers has yielded high strength adhesives that can attach to both high and low surface energy materials, although not equally well. Here, the amount of catechol within a copolymer system was varied for potential tailoring to specific surfaces. Structure-function studies revealed differing trends of optimal catechol content for high energy aluminum versus low energy polytetrafluoroethylene (Teflon^TM) surfaces. Adhesion strengths were optimized with ∼10 mol% catechol for aluminum and ∼41 mol% for Teflon^TM. Varying the catechol incorporation also resulted in changes to wettability, failure modes, and mechanics on these substrates. When considering performance of the entire bulk material, the different surfaces required an altered adhesive-cohesive balance. Tailoring the composition of polymeric adhesives for different surfaces may aid future manufacturing in cases where joining a variety of materials is required.