- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Quantifying Double-Layer Potentials at Liquid–Gas Interfaces from Vibrational Sum-Frequency Generation
摘要： Vibrational sum-frequency generation (SFG) spectroscopy is demonstrated as a fast method to quantify variations of the electric double-layer potential ?0 at liquid?gas interfaces. For this, mixed solutions of nonionic tetraethyleneglycol-monodecylether (C10E4) and cationic hexadecyltrimethylammonium bromide (C16TAB) surfactants were investigated using SFG spectroscopy and a thin-film pressure balance (TFPB). Derjaguin?Landau?Verwey?Overbeek analysis of disjoining pressure isotherms obtained with the TFPB technique provides complementary information on ?0, which we apply to validate the results from SFG spectroscopy. By using a single ?0 value, we can disentangle χ(2) and χ(3) contributions to the O?H stretching modes of interfacial water molecules in the SFG spectra. Having established the latter, we show that unknown double-layer potentials at the liquid?gas interface from solutions with different C16TAB/C10E4 mixing ratios can be obtained from an analysis of SFG spectra and are in excellent agreement with the complementary results from the TFPB technique.
关键词： disjoining pressure,Vibrational sum-frequency generation,electric double-layer potential,thin-film pressure balance,liquid?gas interfaces,surfactants
更新于2025-09-23 15:22:29
-
Bulk-or-interface assignment of heterodyne-detected chiral vibrational sum frequency generation signal by its polarization dependence
摘要： Polarization dependence of heterodyne-detected chiral vibrational sum frequency generation (VSFG) was examined for thin films of polylactic acids and neat limonene liquid far from electronic resonance. The enantiomers of polylactic acid films on silica substrates were successfully distinguished, and their chiral VSFG signals were ascribed not to bulk but to the interfaces by comparing chiral signals observed in reflection in the S-polarized VSFG, P-polarized visible, and P-polarized infrared and P-polarized VSFG, S-polarized visible, and P-polarized infrared polarization combinations with theoretical model calculations. In the same way, the chiral VSFG signal of neat limonene was assigned to bulk, which is consistent with the previous assignment. The method employed for assigning the source of chiral signals to the bulk or the interface may be useful for organic films on substrates with low refractive indices and thick samples.
关键词： limonene,chiral vibrational sum frequency generation,polarization dependence,bulk-or-interface assignment,heterodyne detection,polylactic acid
更新于2025-09-23 15:22:29
-
Broadband models and their consequences on line shape analysis in vibrational sum-frequency spectroscopy
摘要： Vibrational sum-frequency generation (SFG) spectroscopy can provide valuable qualitative and quantitative information about molecular species at surface and buried interfaces. For example, the resonance frequency of a particular chemical function group is revealing of the surface environment, especially when compared to what is observed in bulk IR absorption or Raman scattering spectra. Furthermore, the amplitude of the mode can be related to the molecular orientation, providing a detailed quantitative account of the surface structure. Each of these attributes, however, requires fitting the spectra to some vibrationally resonant line shape. This is particularly challenging when the modes of interest co-exist with broad resonance features, such as water O–H stretching. In this perspective, we examine the merits and consequences of different approaches to fitting homodyne SFG data. We illustrate that, while any model can provide a useful description of the data, no model can accurately and consistently provide even the relative phase deeply encoded in homodyne data without the use of additional information.
关键词： Vibrational sum-frequency generation,homodyne data,surface structure,molecular orientation,line shape analysis,SFG spectroscopy
更新于2025-09-23 15:21:01
-
Hydrogen Bonds and Molecular Orientations of Supramolecular Structure between Barbituric Acid and Melamine Derivative at the Air/Water Interface Revealed by Heterodyne-Detected Vibrational Sum Frequency Generation Spectroscopy
摘要： We studied the supramolecular structure between barbituric acid (pyrimidine-2,4,6(1H,3H,5H)-trione, BA) and an amphiphilic melamine derivative at the air/water interface by heterodyne-detected vibrational sum frequency generation (HD-VSFG) spectroscopy. HD-VSFG measurements in situ showed a positive broad band from 2300 to 2950 cm?1. By comparing the experimental results with ab initio molecular dynamics (AIMD) simulations, we assigned the broad band to the NH stretching modes of BA strongly hydrogen-bonded to the melamine derivative. In addition, we report in situ HD-VSFG spectra of the interfacial supramolecular structure in the CO stretching region. Two CO stretching bands were identified. On the basis of the signs of the C=O bands, we uniquely determined the orientation of BA. The strong hydrogen bonds and the molecular orientations are direct evidence for the supramolecular structure based on complementary hydrogen bonds at the air/water interface.
关键词： Supramolecular Structure,Molecular Orientations,Barbituric Acid,Melamine Derivative,Hydrogen Bonds,Air/Water Interface,Heterodyne-Detected Vibrational Sum Frequency Generation Spectroscopy
更新于2025-09-19 17:13:59