A series of CF3-terminated n-alkyl xanthic acids (AXAs) possessing chain lengths of the form CF3(CH2)nOCS2H (n = 11-18) were synthesized and used to generate self-assembled monolayers (SAMs) on gold surfaces. The wettability of these terminally fluorinated, progressively alkylated self-assembled monolayers (FSAMs) was examined, with specific attention paid to odd-even effects, using a variety of contacting liquids having a wide range of polarities. The organization and packing of the adsorbates within these unique films were evaluated by ellipsometry, X-ray photoelectron spectroscopy, polarization-modulation infrared reflection-absorption spectroscopy (PM-IRRAS), and density functional theory (DFT). Moreover, these FSAMs were compared to SAMs generated from analogous CH3-terminated AXAs, CH3(CH2)nOCS2H (n = 11-18), and alkanethiols, CH3(CH2)nCH2CH2SH (n = 11-18) in efforts to elucidate the influence of the CF3-tailgroup and OCS2H-headgroup on the interfacial properties of the SAMs. Measurements of wettability as a function of chain length revealed the largest odd-even effects ever reported for monolayer systems (e.g., ± 15°).

Surface dipoles give rise to the largest odd-even effects ever reported: Structure and wettability of CF3-terminated n-alkyl xanthic acid self-assembled monolayers

2019 Fall National Meeting

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