Bioinspired surface activators for wet/dry environments through greener epoxy-catechol amine chemistry

Specific chemical interactions found in marine mussels led to a sprout in synthetic surfaces modification approaches especially for wet environment adhesiveness albeit often resulting in poor mechanical robustness. In this contribution, with a view towards robust mechanical adhesion, we present a superior, greener, low cost adhesion "promoter" concept at the interface of aluminium (Al) and epoxy adhesive suitable for both wet and dry conditions by mimicking mussel's adhesion chemistry. Catechol functionalized polymers were realized by the reaction of 3,4 dihydroxyphenylethylamine (DA) with epoxy monomers in 1:1 and 2:1 ratio which upon crosslinking in alkaline medium produced the adhesion promoter primers P1 and P2. P1 under dry condition showed adhesion strength of 9 MPa which is 2-fold and 9-fold higher than uncoated and DA-coated Al specimens respectively. As a highlight, the underwater adhesion strength obtained using P1 is in the range of 7-7.5 MPa, the highest reported fill date. P1 substantially surpassed the adhesive strength offered by commercial primers and conventional etching methods, thanks to the effective interface interactions (binding energy 111.5 kcal/mol) revealed by computational studies. The advantages of this mussel-inspired greener priming approach are manifold for a wide range of applications involving interfaces/load-bearing materials under wet/dry conditions.