Epitaxial transfer through end-group coordination modulates the odd–even effect in an alkanethiol monolayer assembly

Yimer, Yeneneh; Jha, Kshitij C.; Tsige, Mesfin

doi:10.1039/c3nr05671f

Cited by 8 publications

(7 citation statements)

References 54 publications

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“…Self-assembled monolayers (SAMs) are widely used to fabricate surfaces and interfaces with defined compositions, structures, and thicknesses. − Due to their ability to control interfacial structure at molecular scales, SAMs have significant implications in fundamental and technological studies. ,− Interestingly, properties of n -alkanethiolate SAMs depend on whether the molecule has odd or even number of methylene units (carbons in the n -alkanethiols). ,,,,− This odd–even effect manifests as zigzag alternations in chemical, physical, and interface properties in areas like electronic properties, friction behavior, hydrophobicity, and electrochemical properties. ,,− We, ,, and others, ,, are interested in understanding odd–even effect in wetting properties of n -alkanethiolate SAMs to further inform applications of these foundational platform/technologies. This work is part of a series ,− aimed at informing design and developments in SAM-based technologies like molecular tunneling junctions, field-effect transistors, molecular diodes, bioanalytical devices, and surface coating, among many others. ,,,,,− As previously discussed and for simplicity, brevity, and clarity, we utilize static contact anglesa representation of the equilibrium state between the surface and wetting liquid that avoids complexity that may arise from other measurements like advancing ...…”

Section: Introductionmentioning

confidence: 99%

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: Introductionmentioning

confidence: 99%

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

et al. 2016

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“…The criteria for computing hydrogen bonds are based on our previous work on wetting of chemically modified surfaces. 75 Since the hydrogen bond participation rates are higher for water molecules, as expected, inside the amorphous P3HT matrix, a breakdown of the type of hydrogen bond over the course of the simulation is needed to further elucidate the aggregation behavior under confinement.…”

Section: ■ Results and Discussionmentioning

confidence: 93%

“…This is in fact true (Supporting Information, Figure S1), where the hydrogen bond participation rate saturates to 98% for amorphous P3HT (only 3 free water molecules out of 200 at the end), compared to 90% for crystalline P3HT. The criteria for computing hydrogen bonds are based on our previous work on wetting of chemically modified surfaces …”

Section: Resultsmentioning

confidence: 99%

Soft Templating of Water Aggregates Disrupts π–π Stacking in Crystalline Poly(3-hexylthiophene)

et al. 2017

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The π–π stacking robustness of the photoactive layer is key to maintaining efficiency of organic photovoltaics (OPVs). We show local disruption more than 2 Å on average in the π–π stack of crystalline poly(3-hexylthiophene) (P3HT), one of the most common materials used in OPVs, through formation of a chainlike water structure with limited growth and mostly pentameric cluster ends. In contrast, a 3D aggregated water cluster with constant growth is observed in amorphous P3HT. Dynamics of water molecules that form the largest aggregates in crystalline P3HT show the effect of limited mobility, when compared to amorphous P3HT, due to dual confinement from both alkyl side groups and thiophene backbone. We term this dual confinement soft templating and quantify its effect on nature, size, and hydrogen bond participation of water aggregates in crystalline and amorphous P3HT using all-atom molecular dynamics with in-house developed potentials that were previously shown to represent the interfacial and wetting behavior of P3HT systems in good agreement with experiments. Examination of disruption behavior presented for P3HT would allow smart molecular design of photoactive layers.

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“…This was expected because packing densities in this regime have not been found to produce well-ordered SAMs. 21 In the last column of Table 2, we report the standard deviation of the individual headgroups to illustrate the pseudoroughness of each surface.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Chain Flexibility in Self-Assembled Monolayers Affects Protein Adsorption and Surface Hydration: A Molecular Dynamics Study

Beckner

Pfaendtner

2016

J. Phys. Chem. B

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Recent developments in the antifouling properties of Self-Assembled Monolayers (SAMs) have largely focused on increasing the enthalpic association of a hydration layer along the interface of those surfaces with water. However, an entropic penalty due to chain restriction also disfavors biomolecule-surface adsorption. To isolate the effect of this entropic penalty amid changing packing densities, molecular dynamics simulations of explicitly solvated systems of lysozyme and seven monomer length oligo (ethylene glycol) (OEG) SAMs were performed. SAM surfaces were constructed at 100%, 74%, and 53% of a maximum packing (MP) density of 4.97 Å interchain spacing and the effect of chain flexibility was isolated by selectively freezing chain monomers. The rate of protein adsorption as well as the conformation and orientation of the protein upon adsorption were examined. It was found that chain spacing was a strong determinant in adsorption properties while chain flexibility played a secondary role. Of the three packing densities, 74% of MP was the most antifouling with increased antifouling behavior at moderate chain flexibility, i.e. two to four free monomer groups.

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Epitaxial transfer through end-group coordination modulates the odd–even effect in an alkanethiol monolayer assembly

Cited by 8 publications

References 54 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

Soft Templating of Water Aggregates Disrupts π–π Stacking in Crystalline Poly(3-hexylthiophene)

Chain Flexibility in Self-Assembled Monolayers Affects Protein Adsorption and Surface Hydration: A Molecular Dynamics Study

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