Acid−Base Interaction in the Adhesion between Two Solid Surfaces

A study of acid−base interactions in the adhesion between solid surfaces is presented. Adhesion was studied between various OH-functionalized self-assembled monolayer (SAM) surfaces and poly(dimethylsiloxane) (PDMS) cross-linked networks using the contact deformation mechanics method. An increase in adhesion strength was observed in the order of increasing acidity of surface OH protons [Au/S(CH2)11OH < Au/S(C6H4)2OH < Au/S(CH2)15COOH < Au/S(CH2)11PO(OH)2]. Systematic control of surface OH concentration revealed that the strength of adhesion is proportional to the number of surface OH groups but that the relationship is highly nonlinear, probably due to the collective nature of H-bonding between the PDMS chain and surface OH groups. Intermolecular H-bonding at the surface of phosphonic acid (11-mercaptoundecyl phosphonic acid SAMs) results in decreased adhesion.