Two Are Better than One: Bidentate Adsorbates Offer Precise Control of Interfacial Composition and Properties

Mixed self-assembled monolayers (SAMs) generated from perfluoro-, n -alkyl-, and oligo(ethylene glycol)-terminated alkanedithiols were utilized to prepare two-dimensional interfaces with precise composition and wettability. Interfacial control was afforded simply by adjusting the mole fraction of the adsorbates present in the development solutions and was modulated by the dual contributions of the tailgroups of the bidentate thiols. In contrast, the composition and wettability of mixed SAMs generated from traditional monodentate thiols bearing analogous tailgroups failed to track systematically with the mole fractions of the adsorbates in the development solutions, reflecting a greater dependence on solvent/adsorbate interactions. All of the SAMs were thoroughly characterized by contact angle goniometry, ellipsometry, X-ray photoelectron spectroscopy (XPS), and polarization modulation infrared reflection–absorption spectroscopy (PM-IRRAS). Furthermore, solution-phase displacement tests performed to evaluate the stability of the adsorbates as a function of the adsorbate composition of the mixed alkanedithiolate films, provided evidence of the markedly enhanced stability associated with mixed SAMs formed from bidentate adsorbates.