Relative adsorption excess of ions in binary solvents determined by grazing-incidence X-ray fluorescence

Witala, Monika; Konovalov, Oleg; Nygård, Kim

doi:10.1016/j.jcis.2016.09.005

Cited by 3 publications

(3 citation statements)

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“…The signal strengths suggest that, near the surface, there are more cations than anions. Similar relations hold true for KCl in a critical binary mixture of water and 2,6-dimethylpyridine: , the interfacial concentration of ions is diminished near the surface, and close to the surface plane the cation produces higher relative signal than the anion.…”

Section: Introductionsupporting

confidence: 56%

Interactions between Small Inorganic Ions and Uncharged Monolayers on the Water/Air Interface

Peychev

Slavchov

2023

J. Phys. Chem. B

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The interaction of several simple electrolytes with uncharged insoluble monolayers is studied on the basis of tensiometric and potentiometric data for the surface electrolyte solution|air. The induced adsorption of electrolyte on the monolayer is determined via a combination of data for equilibrium spreading pressure and surface pressure versus area isotherms. We show that the monolayer-induced adsorption of electrolyte is not only strongly ionspecific but also surfactant-specific. The comparison between the ionspecific effects on a carboxylic acid monolayer at low pH and an ester monolayer shows that the anion series follows the same order while the cation series reverses. The effect of the electrolyte on the chemical potential of the monolayer shows attraction between the surfactant and the ions at low monolayer densities, but at high surface densities, repulsion seems to come into play. In nearly all investigated cases, a maximum of monolayer-induced electrolyte adsorption is observed at intermediate monolayer densities. This suggests specific interactions between the surfactant headgroup and the ions. The Volta potential data for the monolayers are analyzed on the basis of the equations of quadrupolar electrostatics. The analysis suggests that the ion-specific effect on the Volta potential is due to the ion-specific decrement of the bulk dielectric constant of the electrolyte solution. Moreover, we present evidence that in most cases the effect of the electrolyte on the orientation of the adsorbed dipoles cannot be neglected. Instead, the change in the ion distribution in the electric double layer seems to have a small effect on the Volta potential.

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Section: Introductionsupporting

confidence: 56%

Interactions between Small Inorganic Ions and Uncharged Monolayers on the Water/Air Interface

Peychev

Slavchov

2023

J. Phys. Chem. B

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“…In principle, measurements with D 2 O as well as H 2 O might provide this information but the characteristic signal is expected to be at larger momentum transfer, Q, than can be measured with a significant signal above background. Future work may need to use spectroscopic methods such as X-ray photoelectron spectroscopy (XPS) or the fluorescence method that could be developed for particular ions as described by Witala et al 15 to locate and quantify the metal ions.…”

Section: Introductionmentioning

confidence: 99%

Molecular Organization of an Adsorbed Layer: A Zwitterionic, pH-Sensitive Surfactant at the Air/Water Interface

et al. 2016

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Neutron and X-ray reflection measurements have been used to study the structure of the adsorbed layer of a chelating surfactant at the air/liquid interface. The chelating surfactant 2-dodecyldiethylenetriaminepentaacetic acid (C12-DTPA) has a large head group containing eight donor atoms that can participate in the coordination of metal ions. The donor atoms are also titrating, resulting in an amphoteric surfactant that can adopt a number of differently charged species depending on the pH. Very strong coordination complexes are formed with metal ions, where the metal ion can be considered as part of the surfactant structure, in contrast to monovalent cations that act as regular counter-ions to the negative net charge. Adsorption was investigated over a large concentration interval, from well below the critical micelle concentration (cmc) to five times the cmc. The most striking result is the maximum in the surface excess found around the cmc, which is consistent with previous indications from surface tension measurements. Adding divalent metal ions has a limited effect on the adsorption at the air/liquid interface. The reason is the coordination of the metal ion, resulting in compensating deprotonation of the complex. Small variations in the head group area of different metal complexes are found, correlating to the conditional stability constants. Adding sodium chloride has a significant effect on the adsorption behavior and the results indicate that the protonation equilibrium is more important than the ionic strength effects. From combined fits of the neutron and X-ray data, a model that consists of a thick head group region and a relatively thin dehydrated tail region is found, and it indicates that the tails are not fully extended and that the limiting area per molecule is determined by the bulky head group.

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“…The GIXF in combination with XRR can resolve the distribution of individual elements. This enabled to reveal the unequal partitioning of hydrophilic cations and anions at the liquid-vapor interface in a critical binary mixture of water and 2,6-dimethylpyridine containing KCl below its lower critical temperature [187,188]. The results with a resolution of one excess ion per 200 nm 2 or better provided an unambiguous experimental evidence for microscopic segregation of hydrophilic ions in aqueous critical binary mixtures.…”

Section: Liquid Interfacesmentioning

confidence: 95%

Synchrotron Scattering Methods for Nanomaterials and Soft Matter Research

Narayanan

Konovalov

2020

Materials

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This article aims to provide an overview of broad range of applications of synchrotron scattering methods in the investigation of nanoscale materials. These scattering techniques allow the elucidation of the structure and dynamics of nanomaterials from sub-nm to micron size scales and down to sub-millisecond time ranges both in bulk and at interfaces. A major advantage of scattering methods is that they provide the ensemble averaged information under in situ and operando conditions. As a result, they are complementary to various imaging techniques which reveal more local information. Scattering methods are particularly suitable for probing buried structures that are difficult to image. Although, many qualitative features can be directly extracted from scattering data, derivation of detailed structural and dynamical information requires quantitative modeling. The fourth-generation synchrotron sources open new possibilities for investigating these complex systems by exploiting the enhanced brightness and coherence properties of X-rays.

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Relative adsorption excess of ions in binary solvents determined by grazing-incidence X-ray fluorescence

Cited by 3 publications

References 24 publications

Interactions between Small Inorganic Ions and Uncharged Monolayers on the Water/Air Interface

Interactions between Small Inorganic Ions and Uncharged Monolayers on the Water/Air Interface

Molecular Organization of an Adsorbed Layer: A Zwitterionic, pH-Sensitive Surfactant at the Air/Water Interface

Synchrotron Scattering Methods for Nanomaterials and Soft Matter Research

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