Mixed Phase-Incompatible Monolayers: Toward Nanoscale Anti-adhesive Coatings

This article examines the interfacial properties of phase-incompatible self-assembled monolayer (SAM) films derived from the adsorption of mixtures of bidentate alkanedithiols terminated with oligo(ethylene glycol) and perfluorocarbon tailgroups. Precise control of the composition of the surface was achieved by adjusting the mole fraction of the adsorbates in the developing solution, leading to the ability to tune the interfacial composition and properties. The key driving force for the mixing of the phase-incompatible adsorbates is the strong chelate binding of the bidentate headgroup to the surface of gold. To elucidate this phenomenon, SAMs generated from the analogous monodentate adsorbates were studied alongside those generated from the bidentate adsorbates. Characterization of the SAMs generated from the bidentate adsorbates revealed a 1:3 volume ratio of THF:EtOH solution as the optimal solvent for the generation of SAMs in which both sulfur atoms of the bidentate oligo(ethylene glycol) and perfluorocarbon adsorbates were predominantly bound to the surface of gold. All SAMs were characterized by ellipsometry, contact angle goniometry, X-ray photoelectron spectroscopy, and polarization modulation infrared reflection-absorption spectroscopy. These characterizations revealed the ability to generate films with mixed phase-incompatible groups in which the mole fraction of the adsorbates on the surface mirror those present in the developing solutions, opening up an avenue toward the creation of interfaces not found in nature, with potential use as nanoscale anti-adhesive coatings.