pH Responsive and Oxidation Resistant Wet Adhesivebased on Reversible Catechol–Boronate Complexation

摘要

A smart adhesive capable of binding to a wetted surface was prepared by copolymerizing dopamine methacrylamide (DMA) and 3-acrylamido phenylboronic acid (AAPBA). pH was used to control the oxidation state and the adhesive property of the catechol side chain of DMA and to trigger the catechol–boronate complexation. FTIR spectroscopy confirmed the formation of the complex at pH 9, which was not present at pH 3. The formation of the catechol–boronate complex increased the cross-linking density of the adhesive network. Most notably, the loss modulus values of the adhesive were more than an order of magnitude higher for adhesive incubated at pH 9 when compared to those measured at pH 3. This drastic increase in the viscous dissipation property is attributed to the introduction of reversible complexation into the adhesive network. Based on the Johnson Kendall Roberts (JKR) contact mechanics test, adhesive containing both DMA and AAPBA demonstrated strong interfacial binding properties (work of adhesion (Wadh) = 2000 mJ/m²) to borosilicate glass wetted with an acidic solution (pH 3). When the pH was increased to 9, Wadh values (180 mJ/m²) decreased by more than an order of magnitude. During successive contact cycles,the adhesive demonstrated the capability to transition reversiblybetween its adhesive and nonadhesive states with changing pH. Adhesivecontaining only DMA responded slowly to repeated changes in pH andbecame progressively oxidized without the protection of boronic acid.Although adhesive containing only AAPBA also demonstrated strong wetadhesion (Wadh ∼ 500 mJ/m²), its adhesive properties were not pH responsive. Both DMA and AAPBAare required to fabricate a smart adhesive with tunable and reversibleadhesive properties.