Helical, Disordered, and What that Means: Structural Characterization of a New Series of Methyl 1-Thiaoligo(ethylene Oxide) Self-Assembled Monolayers

Self-assembled monolayers SAMs of a series of linear thiols containing a 1 thiaoligoethylene oxide TOEO moiety, i.e., HSCH2CH2OxCH3, where x 3 - 6, were prepared on polycrystalline gold Au and characterized by reflection absorption infrared spectroscopy RAIRS and spectroscopic ellipsometry SE. For x 5 and 6, the RAIRS data show that the TOEO segment, oriented normal to the substrate, adopts the highly ordered 72 helical structure of the folded-chain crystal polymorph of polyethylene oxide. For x 3 and 4, the RAIRS and SE data indicate disordered, amorphous SAMs with essentially no evidence of the helical conformation in the TOEO segment. These data suggest that, for SAMs with TOEO segments, a minimum of five ethylene oxide units is required to adopt a helical conformation.