Evidence for water ridges at oil–water interfaces: implications for ion transport

Wen, Boyao; Sun, Chengzhen; Zheng, Wenxiu; Bai, Bo; Lichtfouse, Éric

doi:10.1039/c9sm01791g

Cited by 13 publications

(13 citation statements)

References 65 publications

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“…[43][44][45] It was hypothesized from X-ray scattering measurements that the extraction of divalent cations is accomplished via the budding of a micelle at the interface. 35 Analogous work, using a combination of theory and experiment have shown evidence of the presence of water 'fingers', 39 channels, 72 'ridges', 73 and micellar precursors 74 at a range of interfaces. The SFG measurements presented here support this physical picture by demonstrating the existence of molecular aggregates at the neat interface.…”

Section: Resultsmentioning

confidence: 97%

Hydrogen-Bond-Driven Chemical Separations: Elucidating the Interfacial Steps of Self-Assembly in Solvent Extraction

Chowdhury

Doughty

2020

ACS Appl. Mater. Interfaces

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Chemical separations, particularly liquid extractions, are pervasive in academic and industrial laboratories, yet a mechanistic understanding of the events governing their function are obscured by interfacial phenomena that are notoriously difficult to measure. In this work, we investigate the fundamental steps of ligand self-assembly as driven by changes in the interfacial H-bonding network using vibrational sum frequency generation. Our results show how the bulk pH modulates the interfacial structure of extractants at the buried oil/aqueous interface via the formation of unique H-bonding networks that order and bridge ligands to produce self-assembled aggregates. These extended H-bonded structures are key to the subsequent extraction of Co 2+ from the aqueous phase in promoting micelle formation and subsequent ejection of said micelle into the oil phase. The combination of static and time resolved measurements reveals the mechanisms underlying complexities of liquid extractions at high [Co 2+ ]:[DEHPA] ratios by showing an evolution of interfacially assembled structures that are readily tuned on a chemical basis by altering the compositions of the aqueous phase. The results of this work point to new mechanistic principles to design separations through the manipulation of surface charge, electrostatic screening, and the associated H-bonding networks that arise at the interface to facilitate organization and subsequent extraction File list (2)download file view on ChemRxiv DEHPA_pH_MS_submitted.pdf (1.11 MiB) download file view on ChemRxiv Supporting Information_DEHPA_submitted.pdf (384.42 KiB)

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Section: Resultsmentioning

confidence: 97%

Hydrogen-Bond-Driven Chemical Separations: Elucidating the Interfacial Steps of Self-Assembly in Solvent Extraction

Chowdhury

Doughty

2020

ACS Appl. Mater. Interfaces

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“…Dynamic structures forming at the liquid-liquid interface, such as water fingers, water ridges, and chemical "hinges" have been reported as some of the driving mechanisms for interfacial transport. [41][42][43][44][45] Self-assembly of extractant-ion aggregates at the interface can also play a dynamic role in the interfacial ion transport. 21 The ion-specific formation of inverted bilayer with Lu 3+ reported here indicates a possible difference in dynamics of ion transfer with lighter and heavier lanthanides.…”

Section: Discussionmentioning

confidence: 99%

Spontaneous and Ion-Specific Formation of Inverted Bilayers at Air/Aqueous Interface

Nayak

Kumal

Uysal

2021

Preprint

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Amphiphilic lipid-ion interactions at aqueous interfaces drive the assisted ion transport in various biological and industrial systems. In chemical separations of heavy elements, lipids coordinate metal ions and solubilize them in an organic phase. Direct observation of lipid-metal interactions is highly difficult at the buried oil/water interface, and is accessible with limited experiments. Here, we demonstrate that inverted bilayer structures previously observed at oil/aqueous interfaces can also be formed at the air/aqueous interface. This facilitates the easier study of lipid-ion interactions over a wide range of parameters with multiple probes, including synchrotron X-ray reflectivity (XR), X-ray fluorescence near total reflection (XFNTR), and vibrational sum-frequency generation spectroscopy (VSFG). The formation of bilayers is highly sensitive to the metal ion charge density. While Lu 3+ (115 C/mm 3 ) lead to bilayer formation, Nd 3+ (82 C/mm 3 ) and Sr 2+ (33 C/mm 3 ) lead to monolayers. By introducing Lu 3+ ions to preformed lipid monolayers, we extract kinetic parameters corresponding to monolayer to inverted bilayer conversion. Temperature-dependent studies show Arrhenius behavior with an energy barrier of 40 kcal/mol. The kinetics of monolayer to inverted bilayer conversion is also affected by the presence of background salts where thiocyanate accelerates the conversion more than nitrate does. Our results show the outsized importance of ion-specific effects on interfacial structure and kinetics, pointing to their role in chemical separation methods. Finally, this model system can be used to study a wide variety of lipid-ion interactions, opening a new avenue in molecular-scale understanding of these important systems.

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Section: Discussionmentioning

confidence: 99%

Spontaneous and Ion-Specific Formation of Inverted Bilayers at Air/Aqueous Interface

Nayak

Kumal

Uysal

2021

Preprint

View full text Add to dashboard Cite

Amphiphilic lipid-ion interactions at aqueous interfaces drive the assisted ion transport in various biological and industrial systems. In chemical separations of heavy elements, lipids coordinate metal ions and solubilize them in an organic phase. Direct observation of lipid-metal interactions is highly difficult at the buried oil/water interface, and is accessible with limited experiments. Here, we demonstrate that inverted bilayer structures previously observed at oil/aqueous interfaces can also be formed at the air/aqueous interface. This facilitates the easier study of lipid-ion interactions over a wide range of parameters with multiple probes, including synchrotron X-ray reflectivity (XR), X-ray fluorescence near total reflection (XFNTR), and vibrational sum-frequency generation spectroscopy (VSFG). The formation of bilayers is highly sensitive to the metal ion charge density. While Lu3+ (115 C/mm3) lead to bilayer formation, Nd3+ (82 C/mm3) and Sr2+ (33 C/mm3) lead to monolayers. By introducing Lu3+ ions to preformed lipid monolayers, we extract kinetic parameters corresponding to monolayer to inverted bilayer conversion. Temperature-dependent studies show Arrhenius behavior with an energy barrier of 40 kcal/mol. The kinetics of monolayer to inverted bilayer conversion is also affected by the presence of background salts where thiocyanate accelerates the conversion more than nitrate does. Our results show the outsized importance of ion-specific effects on interfacial structure and kinetics, pointing to their role in chemical separation methods. Finally, this model system can be used to study a wide variety of lipid-ion interactions, opening a new avenue in molecular-scale understanding of these important systems.

show abstract

Evidence for water ridges at oil–water interfaces: implications for ion transport

Abstract: We identified a new mode of ion transport across oil–water interfaces, involving a water ridge at low ionic concentrations.

Cited by 13 publications

References 65 publications

Hydrogen-Bond-Driven Chemical Separations: Elucidating the Interfacial Steps of Self-Assembly in Solvent Extraction

Hydrogen-Bond-Driven Chemical Separations: Elucidating the Interfacial Steps of Self-Assembly in Solvent Extraction

Spontaneous and Ion-Specific Formation of Inverted Bilayers at Air/Aqueous Interface

Spontaneous and Ion-Specific Formation of Inverted Bilayers at Air/Aqueous Interface

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