Abstract
Polymers are widely utilized as protective coatings to prevent metal surfaces from wear, corrosion, or bio-fouling. Yet, stability and adhesive properties of polymer to metal bondings are not fully understood at the molecular level. Here, we measured the interaction forces between a gold electrode surface and amine-functionalized polymers (PEG) using a novel electrochemical surface forces apparatus. We examined the potential dependence of specific amine-gold interactions and measured that the binding strength of amine-gold bonds can range from 0.5 to 40k(B)T per binding site, depending on the applied electrochemical potential. Notably, this interaction exhibits a pronounced minimum around the potential of zero charge, where the polymer-gold adhesion is dominated by non-specific interactions between the polymer backbone and electrode surface, consistent with the adhesion of PEG polymers with gold surfaces in the absence of amine functionalization. Further, repulsive hydration interactions were observed to be stronger for amine-terminated PEG compared to non-functionalized PEG, due to increased hydration and presence of counterions in the case of amine-terminated PEG. Our results provide molecular-scale insight into design and optimization of polymer coatings for numerous applications requiring strong, specific binding interactions between polymers and metals (or their native oxides), for example passivating layers in biomedical implants and electronic devices.