Incorporation of Anionic Monomer to Tune the Reversible Catechol-Boronate Complex for pH-Responsive, Reversible Adhesion.

Up to 30 mol % of acrylic acid (AAc) was incorporated into a pH-responsive smart adhesive consisting of dopamine methacrylamide and 3-acrylamido phenylboronic acid. Fourier transform infrared spectroscopy and rheometry confirmed that the incorporation of AAc shifted the pH of catechol-boronate complexation to a more basic pH. Correspondingly, adhesive formulations with elevated AAc contents demonstrated strong adhesion to quartz substrate at a neutral to mildly basic pH (7.5-8.5) based on Johnson-Kendall-Roberts contact mechanics test. When pH was further increased to 9.0, there was a drastic reduction in the measured work of adhesion (18- and 7-fold reduction compared to values measured at pHs 7.5 and 8.5, respectively) due to the formation of catechol-boronate complex. The complex remained reversible, and the interfacial binding property of the adhesive was successfully tuned with changing pH in successive contact cycles. However, an acidic pH (3.0) was required to break the catechol-boronate complex to recover the elevated adhesive property. Adding AAc enables the smart adhesive to function in physiological or marine pH ranges.