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Interfacial Inversion, Interference, and IR Absorption in Vibrational Sum Frequency Scattering Experiments

Sylvie Roke, Saranya Pullanchery Sankara Narayanan, Lei Zhang, Sergey Kulik
2023
Journal paper
Abstract

Molecular interfacial structure greatly determines thepropertiesof nano- and microscale systems. Vibrational sum frequency scattering(SFS) spectroscopy is a unique interface-selective tool to measurethe interfacial vibrational spectrum of sub-micron to micron-scaleobjects dispersed in liquid and solid media. The interfacial structureis extracted from the interfacial susceptibility, a physical propertyderived from the intensity. Here, we describe the effect of infraredabsorption that occurs in a bulk medium that is spectroscopicallycomplex and use the results to investigate the effects of interfacialinversion, interfacial interference, and interfacial interferencecombined with absorption. We use the same three chemicals to do so,hexadecane oil, water, and a neutral Span80 surfactant. For all cases,the effective surface susceptibility can be retrieved from the intensity.We further find that inverting the phases results in different interfacialstructures, even though they are composed of the same three chemicals,and explain this in terms of the different interactions that are necessaryto stabilize the drops: steric stabilization for water drops in oilvs. charge stabilization for oil drops in water. Interfacial interferencecan be used to estimate the surface density of different compounds.

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Ontological neighbourhood
Chemistry
Related concepts (23)
Infrared spectroscopy
Infrared spectroscopy (IR spectroscopy or vibrational spectroscopy) is the measurement of the interaction of infrared radiation with matter by absorption, emission, or reflection. It is used to study and identify chemical substances or functional groups in solid, liquid, or gaseous forms. It can be used to characterize new materials or identify and verify known and unknown samples. The method or technique of infrared spectroscopy is conducted with an instrument called an infrared spectrometer (or spectrophotometer) which produces an infrared spectrum.
Absorption spectroscopy
Absorption spectroscopy refers to spectroscopic techniques that measure the absorption of electromagnetic radiation, as a function of frequency or wavelength, due to its interaction with a sample. The sample absorbs energy, i.e., photons, from the radiating field. The intensity of the absorption varies as a function of frequency, and this variation is the absorption spectrum. Absorption spectroscopy is performed across the electromagnetic spectrum.
Fourier-transform infrared spectroscopy
Fourier-transform infrared spectroscopy (FTIR) is a technique used to obtain an infrared spectrum of absorption or emission of a solid, liquid, or gas. An FTIR spectrometer simultaneously collects high-resolution spectral data over a wide spectral range. This confers a significant advantage over a dispersive spectrometer, which measures intensity over a narrow range of wavelengths at a time. The term Fourier-transform infrared spectroscopy originates from the fact that a Fourier transform (a mathematical process) is required to convert the raw data into the actual spectrum.
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