Spectroscopic evidence for the origin of odd–even effects in self-assembled monolayers and effects of substrate roughness

Liu, Jian; Tevis, Ian D.; Andino, Richard S.; Miller, Christina M.; Ziegler, L. D.; Chen, Xin; Thuo, Martin M.

doi:10.1039/c6cp07580k

Cited by 24 publications

(76 citation statements)

References 43 publications

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“…20 An analogous observation was recently reported using spectroscopy that supports our inference. 47 As expected, 11,13 there was a gradual increase in values of θ s with increase in molecular length; for HD Δθ s, Au AD = 3.9°and Δθ s, Ag Fe-TS = 4.8°while for DEG Δθ s, Au AD = 4.7°and Δθ s, Ag Fe-TS = 3.7°. Similar to water, the values of Δθ s for HD and DEG are not significantly different between Au AD and Ag Fe-TS suggesting that this could be due to a molecule-dominated phenomenon as opposed to substrate.…”

Section: Iiibii Hydrophobicity Of Sams On Rough Surfaces (R Rms > supporting

confidence: 70%

“…This inference is also supported by spectroscopic evidence communicated in an upcoming paper. 47 Wetting properties of SAMs fabricated on Ag Fe-TS and Au AD were investigated by measuring the contact angle on SAMs using water, HD, and diethylene glycol (DEG) as probe liquids (Figure 6a−f and Table 1).…”

Section: Resultsmentioning

confidence: 99%

“…The inference drawn here is in line with observed changes in the intensity and peak-width of the CH 3asym in sum-frequency generation analysis of SAMs on rough and smooth surfaces. 47 The water contact angles on SAMs formed on Au AD and Ag Fe-TS show a significant difference (Figure 7). Average contact angles derived from the Ag Fe-TS surface are slightly lower than those derived from analogous SAMs on Au AD surfaces (average |θ s-Au − θ s-Ag | ≈ 4.2°).…”

Section: Iiibii Hydrophobicity Of Sams On Rough Surfaces (R Rms > mentioning

confidence: 99%

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Effect of Substrate Morphology on the Odd–Even Effect in Hydrophobicity of Self-Assembled Monolayers

et al. 2016

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Surface roughness, often captured through root-mean-square roughness (R), has been shown to impact the quality of self-assembled monolayers (SAMs) formed on coinage metals. Understanding the effect of roughness on hydrophobicity of SAMs, however, is complicated by the odd-even effect-a zigzag oscillation in contact angles with changes in molecular length. We recently showed that for surfaces with R > 1 nm, the odd-even effect in hydrophobicity cannot be empirically observed. In this report, we compare wetting properties of SAMs on Ag and Au surfaces of different morphologies across the R ∼ 1 nm limit. We prepared surfaces with comparable properties (grain sizes and R) and assessed the wetting properties of resultant SAMs. Substrates with R either below or above the odd-even limit were investigated. With smoother surfaces (lower R), an inverted asymmetric odd-even zigzag oscillation in static contact angles (θ) was observed with change from Au to Ag. Asymmetry in odd-even oscillation in Au was attributed to a larger change in θ from odd to even number of carbons in the n-alkanethiol and vice versa for Ag. For rougher surfaces, no odd-even effect was observed; however, a gradual increase in the static contact angle was observed. Increase in the average grain sizes (>3 times larger) on rough surfaces did not lead to significant difference in the wetting properties, suggesting that surface roughness significantly dominated the nature of the SAMs. We therefore infer that the predicted roughness-dependent limit to the observation of the odd-even effect in wetting properties of n-alkanethiols cannot be overcome by creating surfaces with large grain sizes for surfaces with R > 1 nm. We also observed that the differences between Au and Ag surfaces are dominated by differences in the even-numbered SAMs, but this difference vanishes with shorter molecular chain length (≤C).

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Section: Iiibii Hydrophobicity Of Sams On Rough Surfaces (R Rms > supporting

confidence: 70%

Section: Resultsmentioning

confidence: 99%

Section: Iiibii Hydrophobicity Of Sams On Rough Surfaces (R Rms > mentioning

confidence: 99%

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Effect of Substrate Morphology on the Odd–Even Effect in Hydrophobicity of Self-Assembled Monolayers

et al. 2016

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“…From SFG spectroscopic studies, it has been shown that the intensity of asymmetric stretching of the terminal CH 3 group increases generally with the chain length, which is mostly due to a decreasing density of the gauche defect. 29,44…”

Section: Resultsmentioning

confidence: 99%

Quantifying Gauche Defects and Phase Evolution in Self-Assembled Monolayers through Sessile Drops

et al. 2017

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Self-assembled monolayers (SAMs) are widely used in surface modifications, specifically in tuning the surface chemistry of materials. The structure and properties of SAMs have been extensively studied often with sophisticated tools, even for the simplest n -alkanethiolate SAMs. In SAMs, especially in linear n -alkanethiolates, the properties are dependent on the chain length, which is best manifested in the so-called odd–even effect, a simple yet not fully understood phenomenon. One main challenge is fully delineating the origin of length-dependent properties, which can be due to the structure (ideal SAMs), defect evolution, or substrate-molecule effects. This study demonstrates that utilizing the wetting behavior of polar (water) and nonpolar (hexadecane (HD)) solvents on n -alkanethiolate SAMs formed on ultraflat gold and silver surfaces, the evolution of chain-length-dependent gauche defects can be revealed and parameterized through a newly defined dimensionless number (χ). The observation of the odd–even effect in hydrophobicity, however, depends on the thiol chain length, and it was only observed on longer-chain (>C 8 ) molecules. The trend in this odd–even effect demonstrates that there are three main transitions in the nature of wetting, hence structure, across n -alkanethiols. From wetting with HD, the role of dispersive components in wetting reveal that the SAMs are dynamic, which we attribute to rotations associated with previously reported evolution in gauche defects and changes in packing density. Therefore, from re-expression of the Young–Dupre equation, we define a new dimensionless number associated with molecular conformations, whose periodicity mirrors the energetics of Goodman’s conformations of n -alkanes in unbound states and associated four- or two-twist turns. Therefore, we infer that the evolution in surface energy is largely due to molecular conformations and associated relaxations of the bound thiolates.

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“…Figure 1d) that significantly alters the properties of the material ranging from work function, [19][20][21] tribology/wettability, 17,[22][23][24][25] conductivity, 15,[26][27][28][29] plasmonic activity [30][31] among others. 14,16,18,[32][33][34] This material system has been extensively studied since its first introduction in 1946, 35 whereas the passivating oxide has not garnered similar attention. The SAM can be formed via a thermodynamic driven selfassembly process, resulting in a very ordered structure.…”

Section: Liquid Metal Particlementioning

confidence: 99%

Complexity and Opportunities in Liquid Metal Surface Oxides

Martin

Chang

et al. 2020

Chem. Mater.

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The ability of metal alloys to rapidly oxidize in ambient condition presents both a challenge and an opportunity. Herein, we focus on opportunities buried in the passivating oxide of liquid metal particles. Recently described sub-surface complexity and order present an opportunity to frustrate homogeneous nucleation hence enhanced undercooling. Plasticity of the underlying liquid metal surface offers an autonomously repairing sub-surface hence the lowest E0 component dominates the surface unless stoichiometrically limited. This plasticity provides an opportunity to synthesize organometallic polymers that in situ self-assemble to high aspect ratio nanomaterials. An induced surface speciation implies that under the appropriate oxidant tension, the oxide thickness and composition can be tuned, leading to temperature-dependent composition inversion and so-called chameleon metals. The uniqueness of demonstrated capabilities points to the need for more exploration in this small but rather complex part of a metal alloy.

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Spectroscopic evidence for the origin of odd–even effects in self-assembled monolayers and effects of substrate roughness

Cited by 24 publications

References 43 publications

Effect of Substrate Morphology on the Odd–Even Effect in Hydrophobicity of Self-Assembled Monolayers

Effect of Substrate Morphology on the Odd–Even Effect in Hydrophobicity of Self-Assembled Monolayers

Quantifying Gauche Defects and Phase Evolution in Self-Assembled Monolayers through Sessile Drops

Complexity and Opportunities in Liquid Metal Surface Oxides

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