Salicylhydroxamic acid as an electro-responsive and switchable adhesive molecule

This study investigated salicylhydroxamic acid (SHAM) as a new electro-responsive, switchable adhesive molecule for wet adhesive contact. A SHAM-containing polymer was synthesized and evaluated using a customized Johnson-Kendall-Roberts (JKR) contact mechanics setup, where a titanium (Ti) hemisphere simultaneously functioned as the contact substrate and cathodic electrode. Application of electrical potential (0.5-2 V) for 30 s or less reduced the work of adhesion by 84%, while subsequent incubation in a pH 5 buffer restored the original work of adhesion value. Unlike the catechol-containing polymer, which underwent irreversible oxidation to quinone, SHAM demonstrated fully reversible switching without the need for a protective group. Cyclic voltammetry and electrochemical impedance spectroscopy confirmed that both SHAM- and catechol-containing polymers exhibited comparable electrical conductivity, ensuring that the observed differences in adhesion behaviors stemmed from their intrinsic molecular properties. The combination of UV-vis, Fourier transform infrared, and X-ray photoelectron spectroscopy experiments confirmed that the switching mechanism arose from protonation and deprotonation of SHAM, which regulated SHAM's ability to bond to the Ti surface. Conversely, catechol irreversibly oxidized to the poorly adhesive quinone form and failed to regain its initial adhesive properties. SHAM exhibited electro-responsive interfacial bonding capability to a metallic surface under wet conditions and is potentially suitable for designing new switchable adhesives.