Effect of Conductivity on In Situ Deactivation of Catechol-Boronate Complexation-Based Reversible Smart Adhesive.

To reduce the need for elevated electrical potential to deactivate catechol-based smart adhesive and preserve its reversibility, conductive 1-pyrenemethyl methacrylate (PyMA) was incorporated into a catechol and phenylboronic acid-containing adhesive coating immobilized on aluminum (Al) discs. Electrochemical impedance spectroscopy (EIS) indicated that incorporation of 26 mol % of PyMA reduced ionic resistance (Rs) and charge-transfer resistance (Rc) of the coating from over 22 Ω/mm2 to 5.9 and 1.2 Ω/mm2, respectively. A custom-built Johnson-Kendall-Roberts (JKR) contact mechanics test setup was used to evaluate the adhesive property of the coating with in situ applied electricity using a titanium (Ti) sphere both as a test substrate as well as the cathode for application of electricity and the Al disc as the anode. The adhesive coating demonstrated over 95% reduction in the adhesive property when electricity (1-2 V) was applied while the adhesive was in direct contact with the Ti surface. The addition of PyMA enables the deactivation of the adhesive using a voltage as low as 1 V. Both cyclic voltammetry (CV) and attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectra confirmed the formation of catechol-boronate complexation through electrochemical stimulation. Breaking the complex with an acidic buffer (pH 3) recovered the catechol for strong wet adhesion and the coating could be repeatedly deactivated and reactivated using low electrical potential for up to five cycles. Incorporation of both conductive PyMA and boronic acid as the temporary protecting group was required to achieve rapidly switchable adhesive that could be deactivated with low applied voltage.