Salicylhydroxamic Acid as a Novel Switchable Adhesive Molecule.

The feasibility of salicylhydroxamic acid (SHAM) to function as a pH-responsive, switchable adhesive molecule is explored here. Using a custom-built Johnson-Kendall-Roberts contact mechanics test setup, SHAM-containing adhesive demonstrated strong, wet adhesion to various surfaces (glass, titanium, polystyrene and amine-functionalized glass) at pH 5 with adhesive properties that were comparable to those of catechol. Work of adhesion of SHAM decreased by nearly 98% with increasing pH and fully recovered when treated with pH 5. Most impressively, SHAM recovered its adhesive property even after its exposure to pH as high as 11, an indication of superior stability towards base treatment. This result contrasts the case of catechol, which did not recover its initial adhesive property due to irreversible oxidation. Finally, density functional theory calculations was used to confirm that the observed tunable adhesion property was due to the deprotonation of SHAM.