Neutron reflectivity

Cousin, Fabrice; Menelle, A.

doi:10.1051/epjconf/201510401005

Cited by 10 publications

(7 citation statements)

References 15 publications

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“…Pure roughness (i.e., a sharp but geometrically nonflat transition between materials) and interdiffusion (nonsharp but flat transition region) are not distinguishable in specular reflectometry, thus also not in this study, and can both be described by the error function mentioned above (cf. ref ). The fitting procedure consisted of finding the numerical values of the thickness and roughness parameters that best explained the experimentally measured reflectivity, with the relative contribution of pure roughness and interdiffusion (if both are present) being unknown.…”

Section: Methodsmentioning

confidence: 99%

Interactions between Asphaltenes and a Model Demulsifier in Bulk and at an Interface Studied by Small-Angle Neutron Scattering (SANS) and Neutron Reflectometry

et al. 2020

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This article describes neutron reflectometry to probe the structure of the asphaltene layer adsorbed onto a hydrophilic silicon surface and the interactions between asphaltenes and a model demulsifier (pluronic). To start with, asphaltene nanoaggregation is studied in bulk by small-angle neutron scattering (SANS). In pure toluene, asphaltenes form nanoaggregates with sizes that are found to moderately increase when heptane is added. Then, the structure of the asphaltene layer onto a silicon surface is determined by neutron reflectometry. It is first shown that conclusive results on the structure of the adsorbed asphaltene layer can only be determined by varying the scattering length density of the solvent, i.e., by measuring reflectivity curves in various mixtures of D- and H-toluene and by simultaneously fitting all the data sets. The asphaltene layer can be successfully modeled using a single layer; a two-layer model always converges with the second layer having zero thickness. This layer has a thickness of 51 Å, with a low solvation close to the silicon surface (estimated ≈29%). The solvation increases with distance from the silicon oxide layer, reaching finally a value of 91%. Small-angle neutron scattering data indicate that the thickness is close to twice the radius of gyration of asphaltene nanoaggregates in solution. This result indicates that the extent of the asphaltene layer is linked to its self-associative properties in bulk. Finally, using the results obtained by contrast matching to constrain the fitting, the influence of a model demulsifier (pluronic PE 8100) on the asphaltene layer is investigated. In the presence of pluronic, the layer does not protrude as far into the bulk (thickness is reduced) and becomes rougher due to the partial incorporation of pluronic.

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Section: Methodsmentioning

confidence: 99%

Interactions between Asphaltenes and a Model Demulsifier in Bulk and at an Interface Studied by Small-Angle Neutron Scattering (SANS) and Neutron Reflectometry

et al. 2020

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“…Solid lines indicate the simulated reflectivity curves according to the bestmatching parameters of the common volume fraction profile model (see Materials and Methods). The relevant features in the D 2 O contrast are highlighted in the plot by dividing the experimental and simulated reflectivity curves by the Fresnel reflectivity R F of an ideal air-D 2 O interface (48). The reflectivity oscillations around 0.02 Å -1 <q z < 0.06 Å -1 in both neutron contrasts are mainly due to the SLD variations associated with the hydrated extended saccharide layers.…”

Section: Lps Layers At Air-water Interfacesmentioning

confidence: 99%

Structure and Conformation of Wild-Type Bacterial Lipopolysaccharide Layers at Air-Water Interfaces

Micciulla

Gerelli

Schneck

2019

Biophysical Journal

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The outer membrane of Gram-negative bacteria is of great scientific interest because it mediates the action of antimicrobial agents. The membrane surface is composed of lipopolysaccharide (LPS) molecules with negatively charged oligosaccharide headgroups. To a certain fraction, LPSs additionally display linear polysaccharides termed O-side chains (OSCs). Structural studies on bacterial outer surfaces models, based on LPS monolayers at air-water interfaces, have so far dealt only with rough mutant LPSs lacking these OSCs. Here, we characterize monolayers of wild-type LPS from Escherichia coli O55:B5 featuring strain-specific OSCs in the presence of defined concentrations of monovalent and divalent ions. Pressure-area isotherms yield insight into in-plane molecular interactions and monolayer elastic moduli. Structural investigations by x-ray and neutron reflectometry reveal the saccharide conformation and allow quantifying the area per molecule and the fraction of LPS molecules carrying OSCs. The OSC conformation is satisfactorily described by the self-consistent field theory for endgrafted polymer brushes. The monolayers exhibit a significant structural response to divalent cations, which goes beyond generic electrostatic screening.

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“…[48] but can be summarized by understanding that the higher scattering length density (SLD) provided by D 2 O versus H 2 O allows for greater accuracy in bulk water uptake, at the cost of more easily identifying water distribution within the film. [ 49,50 ] The NR measurements of a 30 nm electron‐beam patterned Nafion film (Figures S11 and S12, Supporting Information) were performed on the Platypus instrument [ 51 ] at the OPAL reactor at the Australian Nuclear Science and Technology Organisation (ANSTO). At ANSTO, water activity control was achieved using a modified Hiden Isochema XCS system.…”

Section: Resultsmentioning

confidence: 99%

The Effect of Direct Electron Beam Patterning on the Water Uptake and Ionic Conductivity of Nafion Thin Films

Nguyen

Gluschke

Mostert

et al. 2023

Adv Elect Materials

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The effect of electron‐beam patterning on the water uptake and ionic conductivity of Nafion films using a combination of X‐ray photoelectron spectroscopy, quartz crystal microbalance studies, neutron reflectometry, and impedance spectroscopy is reported. The aim is to further characterize the nanoscale patterned Nafion structures recently used as a key element in novel ion‐to‐electron transducers by Gluschke et al. To enable this, the electron beam patterning process is developed for large areas, achieving patterning speeds approaching 1 cm2 h−1, and patterned areas as large as 7 cm2 for the neutron reflectometry studies. It is ultimately shown that electron‐beam patterning affects both the water uptake and the ionic conductivity, depending on film thickness. Type‐II adsorption isotherm behavior is seen for all films. For thick films (≈230 nm), a strong reduction in water uptake with electron‐beam patterning is found. In contrast, for thin films (≈30 nm), electron‐beam patterning enhances water uptake. Notably, for either thickness, the reduction in ionic conductivity arising from electron‐beam patterning is kept to less than an order of magnitude. Mechanisms are proposed for the observed behavior based on the known complex morphology of Nafion films to motivate future studies of electron‐beam processed Nafion.

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Neutron reflectivity

Cited by 10 publications

References 15 publications

Interactions between Asphaltenes and a Model Demulsifier in Bulk and at an Interface Studied by Small-Angle Neutron Scattering (SANS) and Neutron Reflectometry

Interactions between Asphaltenes and a Model Demulsifier in Bulk and at an Interface Studied by Small-Angle Neutron Scattering (SANS) and Neutron Reflectometry

Structure and Conformation of Wild-Type Bacterial Lipopolysaccharide Layers at Air-Water Interfaces

The Effect of Direct Electron Beam Patterning on the Water Uptake and Ionic Conductivity of Nafion Thin Films

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