Sum frequency generation spectroscopy of fluorinated organic material-based interfaces: a tutorial review

Sakunkaewkasem, Siwakorn; Deleon, Daniela; Choi, Yunsoo; Tran, Hung-Vu; Marquez, Maria D.; Baldelli, Steven; Lee, T. Randall

doi:10.1039/d2an02020c

Cited by 3 publications

(2 citation statements)

References 109 publications

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“…In particular, the detection depth of SFG spectroscopy is usually at the nanoscale, − while the definition of interfacial depth in macro-experiments such as zeta potential is ambiguous; (2) more advanced experimental techniques on the atomic scale are yet to be developed. Most experiments aimed at identifying the acid–base nature of interfaces rely on indirect measurements. − ,,, Although the OH dynamics of water molecules at the first interfacial hydration layer can be observed by vibrational SFG spectroscopy, − which helped to probe the interfacial protons of a 1 M HCl solution, the in-operando detection of ionic distribution along the interfacial depth of the neutral water system with the standard surface-science methods is still challenging. − By combining with simulation technologies, deeper atomic-scale perspectives can be achieved. In terms of theoretical computations, the modeling scale of accurate AIMD, which is usually limited to simulations for hundreds of water molecules and hundreds of picoseconds due to the expensive computational cost, is far from the actual interface scale and dynamic time scale, so it is possible that these simulation results were slightly deviated.…”

Section: Introductionmentioning

confidence: 99%

Double-Layer Distribution of Hydronium and Hydroxide Ions in the Air–Water Interface

Zhang,

Feng,

2024

ACS Phys. Chem Au

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The acid−base nature of the aqueous interface has long been controversial. Most macroscopic experiments suggest that the air−water interface is basic based on the detection of negative charges at the interface that indicates the enrichment of hydroxides (OH − ), whereas microscopic studies mostly support the acidic air−water interface with the observation of hydronium (H 3 O + ) accumulation in the top layer of the interface. It is crucial to clarify the interfacial preference of OH − and H 3 O + ions for rationalizing the debate. In this work, we perform deep potential molecular dynamics simulations to investigate the preferential distribution of OH − and H 3 O + ions at the aqueous interfaces. The neural network potential energy surface is trained based on density functional theory calculations with the SCAN functional, which can accurately describe the diffusion of these two ions both in the interface and in the bulk water. In contrast to the previously reported single ion enrichment, we show that both OH − and H 3 O + surprisingly prefer to accumulate in interfaces but at different interfacial depths, rendering a double-layer ionic distribution within ∼1 nm near the Gibbs dividing surface. The H 3 O + preferentially resides in the topmost layer of the interface, but the OH − , which is enriched in the deeper interfacial layer, has a higher equilibrium concentration due to the more negative free energy of interfacial stabilization [−0.90 (OH − ) vs −0.56 (H 3 O + ) kcal/mol]. The present finding of the ionic double-layer distribution may qualitatively offer a self-consistent explanation for the long-term controversy about the acid−base nature of the air−water interface.

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Section: Introductionmentioning

confidence: 99%

Double-Layer Distribution of Hydronium and Hydroxide Ions in the Air–Water Interface

Zhang,

Feng,

2024

ACS Phys. Chem Au

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“…Among the various probing methods, sum frequency generation vibration spectroscopy (SFG-VS) is a second-order nonlinear technique with unique interface sensitivity and selectivity; it can reveal the molecular-level structures and their changes at the interfaces. − For example, Maia and Miranda studied the chain structures of conjugated polymers at the buried interface between polymers and metals and observed different thiophene ring orientations on different metallic substrates or from different film-forming processes . Li et al investigated the buried interface between nylon and modified polyethylene and reported that the interfacial adhesion between nylon and modified polyethylene was enhanced by the formation of a covalent bond via the consumption of N–H groups at the buried interface .…”

Section: Introductionmentioning

confidence: 99%

Revealing Interfacial Structures between Silica and Epoxy Adhesive via Spectroscopy and Morphological and Adhesion Tests

Zhang,

Ding

et al. 2024

J. Phys. Chem. C

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Adhesives and glass are commonly used in electronic packaging. The macroscopic and microscopic (molecular-level) structures at the interface between glass and epoxy adhesives have attracted a great deal of interest in the field of surface analysis. In many previous studies, sum frequency generation vibration spectroscopy (SFG-VS) with a total internal reflection (TIR) silica prism was used to probe these types of interfaces. However, for adhesives with relatively high refractive indexes, the requirement of a TIR geometry is not matched, and the origin of SFG-VS signals from the interface involving the prism and adhesive is complicated. Many efforts have been made to resolve this issue. This study provides an approach to analyze the linear and nonlinear optical transmission and emission in a silica−epoxy adhesive−silica sandwich sample with different adhesive thicknesses (i.e., 1.5, 4.5, and 13.5 μm). The origin of SFG-VS signals and structural information in the adhesive were revealed from spectroscopy, morphological, and adhesion tests. It was observed that an insufficient adhesive thickness leads to void structures in the adhesive layer, generating a relatively high SFG-VS signal at the adhesive−air interface. However, samples with a filled adhesive layer emit much weaker SFG signals. Lap shear tests, energy-dispersive X-ray imaging, scanning electron microscopy, and SFG-VS with the introduction of liquids into the sample were used to confirm conclusions obtained from linear and nonlinear optical measurements. This study provides a straightforward experimental approach to analyze the relatively complicated interfaces involving polymers.

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Extracting the Heterogeneous 3D Structure of Molecular Films Using Higher Dimensional SFG Microscopy

Fellows,

John,

Wolf

et al. 2024

J. Phys. Chem. Lett.

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Ultrathin molecular films are widespread in both natural and industrial settings, where details of the molecular structure such as density, outof-plane tilt angles, and in-plane directionality determine their physicochemical properties. Many of these films possess important molecular-to-macroscopic heterogeneity in these structural parameters, which have traditionally been difficult to characterize. Here, we show how extending sum-frequency generation (SFG) microscopy measurements to higher dimensionality by azimuthal-scanning can extract the spatial variation in the three-dimensional molecular structure at an interface. We extend the commonly applied theoretical assumptions used to analyze SFG signals to the study of systems possessing in-plane anisotropy. This theoretical framework is then applied to a phase-separated mixed lipid monolayer to investigate the variation in molecular density and 3D orientation across the chirally packed lipid domains. The results show little variation in out-of-plane structure but a distinct micron-scale region at the domain boundaries with a reduction in both density and in-plane ordering.

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Sum frequency generation spectroscopy of fluorinated organic material-based interfaces: a tutorial review

Abstract: Molecular interactions at interfaces have a significant effect on the wetting properties of surfaces on a macroscale.

Cited by 3 publications

References 109 publications

Double-Layer Distribution of Hydronium and Hydroxide Ions in the Air–Water Interface

Double-Layer Distribution of Hydronium and Hydroxide Ions in the Air–Water Interface

Revealing Interfacial Structures between Silica and Epoxy Adhesive via Spectroscopy and Morphological and Adhesion Tests

Extracting the Heterogeneous 3D Structure of Molecular Films Using Higher Dimensional SFG Microscopy

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