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Isostructural Self-Assembled Monolayers, Part 2. Methyl-1-(3-Mercaptopropyl)-Oligo(Ethylene Oxide)s

Published

Author(s)

David J. Vanderah, T Parr, Vitalii I. Silin, Curtis W. Meuse, Richard S. Gates, H La, Gintaras Valincius

Abstract

The structural order and, for some, the ordering conditions of the self-assembled monolayers (SAMs) of HSCH2CH2CH2O(EO)xCH3, where EO = CH2CH2O, and x = 3 to 9, on polycrystalline gold (Au) were determined by reflection absorption infrared spectroscopy (RAIRS), spectroscopic ellipsometry (SE), and electrochemical impedance spectroscopy (EIS). For x = 5 to 7, RAIRS and SE data show that the oligo(ethylene oxide) [OEO] segments adopt the near single phase, 7/2 helical conformation of the folded-chain crystal polymorph of crystalline poly(ethylene oxide), oriented normal to the substrate, and are the first examples of OEO-SAMs to attain this highly ordered, helical conformation where the OEO segment is separated from the Au-sulfur headgroup by a polymethylene chain. For x = 4, 8 and 9, the SAMs are largely helical but show evidence of non-helical conformations and establish the upper and lower limits of the isostructural set. For x = 3, the SAMs are largely disordered containing some all-trans conformation. SAM order as a function of immersion time from 100% water and 95% ethanol indicate that the HSCH2CH2CH2O(EO)5 7CH3 SAMs, which have three carbons separating the sulfur from the first oxygen atom, order faster and under a wider range of conditions than -alkyl 1-thiaolio(ethylene oxide)s [HSEOxR] SAMs, reported earlier (R = CH3: Vanderah, D.J., et al. Langmuir 2002, 18, 4674 and Vanderah, D.J., et al. Langmuir 2003, 19, 2612; R = C18H37: Vanderah, D.J., et al. Langmuir 2003, 19, 2612), which have two carbons between the sulfur and the first oxygen atom.
Citation
Langmuir
Volume
20
Issue
4

Keywords

isostructural series, oligo(ethylene oxide)s, self-assembled monolayers

Citation

Ross, D. , Parr, T. , Silin, V. , Meuse, C. , Gates, R. , La, H. and Valincius, G. (2004), Isostructural Self-Assembled Monolayers, Part 2. Methyl-1-(3-Mercaptopropyl)-Oligo(Ethylene Oxide)s, Langmuir (Accessed April 23, 2024)
Created February 17, 2004, Updated February 17, 2017