A novel X-ray diffractometer for studies of liquid–liquid interfaces

Murphy, Bridget; Greve, M.; Runge, Benjamin; Koops, C. T.; Elsen, Annika; Stettner, J.; Seeck, O. H.; Magnussen, Olaf M.

doi:10.1107/s1600577513026192

Cited by 43 publications

(35 citation statements)

References 58 publications

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“…The setup is inspired by concepts employed in our previous high energy X-ray reectivity studies on deeply buried interfaces, 21,23,39 and recent developments in the eld of electrochemical in situ X-ray scattering techniques. 40,41 For visual sample inspection during alignment and measurements in a vacuum or inert Fig. 1 Sketch of the setup for in situ XRR experiments (total height 165 mm).…”

Section: In Situ Setupmentioning

confidence: 99%

Molecular scale structure and dynamics at an ionic liquid/electrode interface

et al. 2018

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After a century of research, the potential-dependent ion distribution at electrode/electrolyte interfaces is still under debate. In particular for solvent-free electrolytes such as room-temperature ionic liquids, classical theories for the electrical double layer are not applicable. Using a combination of in situ high-energy X-ray reflectivity and impedance spectroscopy measurements, we determined this distribution with sub-molecular resolution. We find oscillatory charge density profiles consisting of alternating anion- and cation-enriched layers at both cathodic and anodic potentials. This structure is shown to arise from the same ion-ion correlations dominating the liquid bulk structure. The relaxation dynamics of the interfacial structure upon charging/discharging were studied by impedance spectroscopy and time resolved X-ray reflectivity experiments with sub-millisecond resolution. The analysis revealed three relaxation processes of vastly different characteristic time scales: a 2 ms scale interface-normal ion transport, a 100 ms scale molecular reorientation, and a minute scale lateral ordering within the first layer.

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Section: In Situ Setupmentioning

confidence: 99%

Molecular scale structure and dynamics at an ionic liquid/electrode interface

et al. 2018

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“…x-ray measurements are rather challenging, and require special setups. [29][30][31] In fact, only a single x-ray study of a LC surface phase of an RTIL, [C 22 mim][NTf 2 ], has been published to date, identifying the phase as smectic A, and determining the temperature dependence of the thickness of the LC surface layer. 32 Here we report an x-ray study of the liquid/air surface of another long-chain RTIL,…”

Section: Introductionmentioning

confidence: 99%

Surface Phases and Surface Freezing in an Ionic Liquid

Pontoni

Haddad

Murphy³

et al. 2019

J. Phys. Chem. C

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Room temperature ionic liquids (RTILs), a novel class of liquid salts, are intensively studied for their basic science and numerous emerging applications. When undercooled, RTILs comprising long alkyl chains often exhibit liquid crystal (LC) bulk phases. However, only one molecular-resolution experimental structure study was published for their LC surface phases. We measured the temperature evolution of another LC surface phase, using surface specificÅ-resolution x-ray methods. This phase's existence range, 90 • C, much exceeds the corresponding bulk phase's 3 • C. Its thickness, L, confirms the theory-predicted logarithmic temperature dependence, with an amplitude equalling the bulk correlation length. Surprisingly, at L's divergence temperature, a ∼ 20Å-thick, hexagonally-packed, crystalline monolayer forms at, and fully covers, the sample's surface. It is identified as a surface-frozen Langmuir-Gibbs film, and fundamentally differs from the only reported RTIL surface crystal, a Coulomb-dominated, four-layer, island phase, covering only 5%-15% of the surface.

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“…The measurements were carried out at an x-ray energy of 25 keV at the high-resolution beamline P08 [36] of the PETRA III synchrotron source at DESY (Hamburg, Germany) using the LISA liquid surface diffractometer [37,38]. The special geometry of the diffractometer allows varying the x-ray's incidence angle without moving the sample, thus avoiding movement-associated disturbances to the fragile liquid-liquid interface.…”

Section: B X-ray Measurementsmentioning

confidence: 99%

Temperature- and potential-dependent structure of the mercury-electrolyte interface

Runge¹,

Festersen²,

Koops³

et al. 2016

Phys. Rev. B

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The atomic-scale structure of the mercury-electrolyte (0.01 M NaF) interface was studied as a function of temperature and potential by x-ray reflectivity and x-ray diffuse scattering measurements. The capillary wave contribution is determined and removed from the data, giving access to the intrinsic surface-normal electron density profile at the interface, especially to the surface layering in the Hg phase. A temperature dependent roughness anomaly known from the Hg-air interface is found to persist also at the Hg-electrolyte interface. Additionally, a temperature dependence of the layering period was discovered. The increase in the layer spacing with increasing temperature is approximately four times lager than the increase expected from thermal expansion. Finally, the interface is found to broaden towards the electrolyte side as the potential becomes more negative, in agreement with the Schmickler-Henderson theory. Our results favor a model for the interface structure, which is different to the model formerly used in comparable studies.

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A novel X-ray diffractometer for studies of liquid–liquid interfaces

Cited by 43 publications

References 58 publications

Molecular scale structure and dynamics at an ionic liquid/electrode interface

Molecular scale structure and dynamics at an ionic liquid/electrode interface

Surface Phases and Surface Freezing in an Ionic Liquid

Temperature- and potential-dependent structure of the mercury-electrolyte interface

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