Influence of Charged Site Density on Local Electric Fields and Polar Solvent Organization at Oxide Interfaces

Dadashi, Somaiyeh; Parshotam, Shyam; Mandal, Bijoya; Rehl, Benjamin; Gibbs, Julianne M.; Borguet, Eric

doi:10.1021/acs.jpcc.4c00306

Cited by 3 publications

References 65 publications

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Detecting Centrosymmetric Molecular Ions at an Interface with Vibrational Sum Frequency Generation Spectroscopy

Mandal,

Dadashi,

Kumagai

et al. 2024

J. Phys. Chem. C

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Under the electric dipole approximation, second-order nonlinear optical phenomena, such as vibrational sum frequency generation (vSFG) and second harmonic generation (SHG), are forbidden in centrosymmetric environments, making them surfacespecific processes where the centrosymmetry is inherently broken and suitable for studying interfacial chemistry. Although the underlying theory of vSFG/SHG pertaining to centrosymmetry has been extensively studied, fundamental questions remain to be addressed. For example, what leads to the breaking of centrosymmetry in a centrosymmetric molecule at interfaces? Is the interface capable of perturbing the environment of a centrosymmetric molecule, rendering it vSFG active? At what point does the centrosymmetric molecule lose its centrosymmetry to become vSFG active? In this work, we address such basic questions by studying the vSFG response from the azido stretch of N 3 − , a centrosymmetric molecule, at the α-Al 2 O 3 (0001)/H 2 O interface. We observed the azido asymmetric stretch vSFG response at the aqueous alumina interface. There are several possible mechanisms that render this centrosymmetric molecule vSFG active, including dipole and quadrupole mechanisms. Therefore, we analyzed the possible vSFG mechanisms of the azide signal via electronic structure calculations and AIMD simulations. We show that a uniaxial electric field acting on centrosymmetric azide, whose modes are either IR or Raman active but never both, can make modes simultaneously IR and Raman active, but this turns out not to be enough to explain the sum frequency activity that we observe. The electronic structure calculations revealed that azide has sufficiently large quadrupolar susceptibility, which provides the dominant contribution in the azide vSFG response.

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Detecting Centrosymmetric Molecular Ions at an Interface with Vibrational Sum Frequency Generation Spectroscopy

Mandal,

Dadashi,

Kumagai

et al. 2024

J. Phys. Chem. C

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Second harmonic generation null angle polarization analysis for determining interfacial potential at charged interfaces

Egemba,

Ohno

2024

The Journal of Chemical Physics

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Methods of quantifying the electrostatics of charged interfaces are important in a range of research areas. The surface-selective nonlinear optical technique second harmonic generation (SHG) is a sensitive probe of interfacial electrostatics. Recent work has shown that detection of the SHG phase in addition to its amplitude enables direct quantification of the interfacial potential. However, the experimental challenge of directly detecting the phase interferometrically with sufficient precision and stability has led to the proposal and development of alternative techniques to recover the same information, notably through wavelength scanning or angle scanning, each of which has their own associated experimental challenges. Here, we propose a new polarization-based approach to recover the required phase information, building upon the previously established nonlinear optical null ellipsometry (NONE) technique. Although NONE directly returns only relative phase information between different tensor elements of the second-order susceptibility, it is shown that a symmetry relation that connects the tensor elements of the potential-dependent third-order susceptibility can be used to generate the absolute phase reference required to calculate the interfacial potential. The sensitivity of the technique to potential at varying surface charge densities and ionic strengths is explored by means of simulated data of the silica:water interface. The error associated with the use of the linearized Poisson–Boltzmann approximation is discussed and compared to the error associated with the precision of the measured NONE null angles. Overall, the results suggest that NONE is a promising approach for performing phase-resolved SHG based quantification of interfacial potentials that experimentally requires only the addition of standard polarization optics to the basic single-wavelength, fixed-angle SHG apparatus.

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Ion Adsorption and Hydration Superlubricity

Han,

Zhang,

Luo

2024

Adsorption - Fundamental Mechanisms and Applications [Working Title]

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The surface-water interactions are pivotal in interfacial functions and properties relevant in many natural processes, particularly the lubrication systems of living organisms, like the articular cartilage, oral mucosa, cardiovascular system, muscle, and tendon tissue. The ion adsorption often determines interfacial lubrication performance, especially hydration superlubricity, which depends on the surface charge characteristics and ion types. The hydration superlubricity mechanism has been well understood over the past 30 years, which further promotes the exploration and development of artificial hydration lubrication materials inspired by nature. This review first introduces the basic properties of the solid–liquid interface and the superlubricity system related to hydrated ions. Then, the influencing factors and mechanism of interfacial ion adsorption on hydration superlubricity are presented. Subsequently, negatively charged materials based on overall modification are summarized, including modified PEEK and modified UHMWPE with ultra-low friction coefficient and ultra-low wear rate. Finally, the potential application of such materials in artificial joints and underwater equipment systems are put forward. It is projected that interest in ion adsorption and hydration superlubricity from the basic science and engineering communities will continue to accelerate in the near future, accompanied by the concept of superlubricitive engineering.

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Influence of Charged Site Density on Local Electric Fields and Polar Solvent Organization at Oxide Interfaces

Cited by 3 publications

References 65 publications

Detecting Centrosymmetric Molecular Ions at an Interface with Vibrational Sum Frequency Generation Spectroscopy

Detecting Centrosymmetric Molecular Ions at an Interface with Vibrational Sum Frequency Generation Spectroscopy

Second harmonic generation null angle polarization analysis for determining interfacial potential at charged interfaces

Ion Adsorption and Hydration Superlubricity

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