Variation Small-angle Neutron Scattering Research Articles

Detailed Catalyst Layer Structure of Proton Exchange Membrane Fuel Cells from Contrast Variation Small-Angle Neutron Scattering

Detailed Catalyst Layer Structure of Proton Exchange Membrane Fuel Cells from Contrast Variation Small-Angle Neutron Scattering

Ion Atmosphere of Wormlike Micelles Profiled by Contrast Variation Small-Angle Neutron Scattering.

Structural studies of wormlike micelles have so far mostly focused on the conformational properties of surfactant aggregates. The diffuse ionic atmosphere, which has a profound influence on various micellization phenomena such as thermodynamic stability and structural polymorphism, remains largely unexplored experimentally. In this report a strategy of contrast variation small-angle neutron scattering for this crucial structural study is outlined. Underlined by a general criterion established for unbiasedly identifying the length scale relevant to charge association from the spectral evolution, our analytical framework can provide a quantitative description of counterion distribution in a mathematically tractable manner. Our method can be conveniently extended to facilitate structural studies of complex multicomponent systems using contrast variation neutron scattering.

The Multilevel Structure of Sulfonated Syndiotactic-Polystyrene Model Polyelectrolyte Membranes Resolved by Extended Q-Range Contrast Variation SANS.

Membranes based on sulfonated synditoactic polystyrene (s-sPS) were thoroughly characterized by contrast variation small-angle neutron scattering (SANS) over a wide Q-range in dry and hydrated states. Following special sulfonation and treatment procedures, s-sPS is an attractive material for fuel cells and energy storage applications. The film samples were prepared by solid-state sulfonation, resulting in uniform sulfonation of only the amorphous phase while preserving the crystallinity of the membrane. Fullerenes, which improve the resistance to oxidation decomposition, were incorporated in the membranes. The fullerenes seem to be chiefly located in the amorphous regions of the samples, and do not influence the formation and evolution of the morphologies in the polymer films, as no significant differences were observed in the SANS patterns compared to the fullerenes-free s-sPS membranes, which were investigated in a previous study. The use of uniaxially deformed film samples, and neutron contrast variation allowed for the identification and characterization of different structural levels with sizes between nm and μm, which form and evolve in both the dry and hydrated states. The scattering length density of the crystalline regions was varied using the guest exchange procedure between different toluene isotopologues incorporated into the sPS lattice, while the variation of the scattering properties of the hydrated amorphous regions was achieved using different H2O/D2O mixtures. Due to the deformation of the films, the scattering characteristics of different structures can be distinguished on specific detection sectors and at different detection distances after the sample, depending on their size and orientation.

Contrast Variation Small Angle Neutron Scattering Investigation of Micro- and Nano-Sized TATB.

Small angle neutron scattering (SANS) with contrast variation was used to characterize the fractal behavior and embedded porosity of micro/nano-sized 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) crystallites, gauging the effects of particle sizes on the microstructural features. Scattering results reveal that the external surface of micro-sized TATB crystallites are continuous and smooth interfaces and their internal pores display a surface fractal structure (surface fractal dimension 2.15 < DS < 2.25), while the external surface of nano-sized TATB particles exhibit a surface fractal structure (surface fractal dimension 2.36 < DS < 2.55) and their internal pores show a two-level volume fractal structure (large voids consist of small voids). The voids volume fraction of nano-sized TATB particles are found increased distinctively when compared with micro-sized TATB particles on length scale between 1 nm and 100 nm. Specific surface areas are also estimated based on Porod law method, which are coincident with Brunauer-Emmett-Teller (BET) measurements. The contrast variation technique distinguishes the information of internal voids from external surface, suggesting SANS is a powerful tool for determining the microstructural features, which can be used to establish the relationship between microstructures and properties of micro/nano-energetic materials.

Evolution of the Interfacial Structure of a Catalyst Ink with the Quality of the Dispersing Solvent: A Contrast Variation Small-Angle and Ultrasmall-Angle Neutron Scattering Investigation.

The electrocatalyst layer (ECL) of the proton-exchange membrane fuel cell (PEMFC) is commonly fabricated from colloidal catalyst ink containing carbon-supported catalyst nanoparticles (NPs), ionomer stabilizer, and dispersion medium (DM). The structure, stability, and aggregate size distribution of fuel cell catalyst ink are critically dependent on the quality of DM. However, understanding of the influence of the quality of DM on the hierarchical structure of the ECL is lacking. This work presents a systematic investigation of the effects of reducing alcohol content in isopropyl alcohol/water (IPA/H2O) binary mixtures as DM on the structural evolution of water-rich (green) catalyst ink using contrast-variation small-angle and ultrasmall-angle neutron scattering techniques. Both qualitative and quantitative information are extracted from the data to obtain information about the size, structure, and organization of the catalyst ink using different model functions fit to the experimental data. The catalyst ink prepared using 70% IPA (commonly employed in industry and extensively reported in the literature) is shown to consist of randomly distributed globular carbon aggregates (mean radius of gyration of ∼178.9 nm) stabilized by an ionomer mass fractal shell (thickness of ∼13.0 nm), which is dispersed in the matrix of rodlike (∼1.3 nm radius and ∼35.0 nm length) negatively surface-charged ionomer NPs. These well characterized baseline data are then compared and contrasted with DM formulations of lower IPA content. A sequential reduction in IPA content of DM shows a progressive increase in the ionomer NP radius and electrostatic repulsion, concomitantly with the decrease in the carbon aggregate size and ionomer shell thickness of the catalyst ink. Therefore, the changes in the interfacial structure via adjustments of the DM composition can be used as a controlling parameter to tailor the hierarchical structure of the colloidal fuel cell catalyst ink and to further optimize the performance of the ECL.

Mesoscopic Investigation of an “Immiscible” Cyclohexane and Water Micro-mixture in Carbon Micropores by Contrast Variation Small-angle Neutron Scattering

Microspaces can simultaneously capture “immiscible” molecules such as cyclohexane and water due to fluid-surface interactions. We investigated the mesoscopic structure of cyclohexane and water co-adsorbed in carbon micropores using contrast variation small-angle neutron scattering (CV-SANS). The results show that cyclohexane tends to adsorb near the carbon surface and that both molecules form relatively small domains (<1 nm).

Deuterium Labeling Together with Contrast Variation Small-Angle Neutron Scattering Suggests How Skp Captures and Releases Unfolded Outer Membrane Proteins.

In Gram-negative bacteria, the chaperone protein Skp forms specific and stable complexes with membrane proteins while they are transported across the periplasm to the outer membrane. The jellyfish-like architecture of Skp is similar to the eukaryotic and archaeal prefoldins and the mitochondrial Tim chaperones, that is the α-helical "tentacles" extend from a β-strand "body" to create an internal cavity. Contrast variation small-angle neutron scattering (SANS) experiments on Skp alone in solution and bound in two different complexes to unfolded outer membrane proteins (uOMPs), OmpA and OmpW, demonstrate that the helical tentacles of Skp bind their substrate in a clamp-like mechanism in a conformation similar to that previously observed in the apo crystal structure of Skp. Deuteration of the uOMP component combined with contrast variation analysis allowed the shapes of Skp and uOMP as well as the location of uOMP with respect to Skp to be determined in both complexes. This represents unique information that could not be obtained without deuterium labeling of the uOMPs. The data yield the first direct structural evidence that the α-helical Skp tentacles move closer together on binding its substrate and that the structure of Skp is different when binding different uOMPs. This work presents, by example, a tutorial on performing SANS experiments using both deuterium labeling and contrast variation, including SANS theory, sample preparation, data collection, sample quality validation, data analysis, and structure modeling.

Contrast Variation Small Angle Neutron Scattering by Dynamic Nuclear Polarization: A Case of Time-of-Flight Method in J-PARC

Contrast Variation Small Angle Neutron Scattering by Dynamic Nuclear Polarization: A Case of Time-of-Flight Method in J-PARC

Correlating Structure and Photocurrent for Composite Semiconducting Nanoparticles with Contrast Variation Small-Angle Neutron Scattering and Photoconductive Atomic Force Microscopy

Aqueous dispersions of semiconducting nanoparticles have shown promise as a robust and scalable platform for the production of efficient polymer/fullerene active layers in organic photovoltaic applications. Semiconducting nanoparticles are a composite of both an n-type and p-type semiconductor contained within a single nanoparticle. In order to realize efficient organic solar cells from these materials, there is a need to understand how the size and internal distribution of materials within each nanoparticle contributes to photocurrent generation in a nanoparticle-derived device. Therefore, characterizing the internal distribution of conjugated polymer and fullerene within the dispersion is the first step to improving performance. To date, study of polymer/fullerene structure within these nanoparticles has been limited to microscopy techniques of deposited nanoparticles. In this work, we use contrast variation with small-angle neutron scattering to determine the internal distribution of poly(3-hexylthiophene) and [6,6]phenyl-C61-butyric acid methyl ester inside the composite nanoparticles as a function of formulation while in dispersion. On the basis of these measurements, we connect the formulation of these nanoparticles with their internal structure. Using electrostatic deposited monolayers of these nanoparticles, we characterize intrinsic charge generation using photoconductive atomic force microscopy and correlate this with structures determined from small-angle neutron scattering measurements. These techniques combined show that the best performing composite nanoparticles are those that have a uniform distribution of conjugated polymer and fullerene throughout the nanoparticle volume such that electrons and holes are easily transported out of the particle.

STRUCTURE ANALYSES OF SWOLLEN RUBBER–CARBON BLACK SYSTEMS BY USING CONTRAST VARIATION SMALL-ANGLE NEUTRON SCATTERING

Abstract In a previous study [Takenaka et al., Macromolecules 42, 308 (2009)], we have investigated the polymer layers absorbed on silica (Si) particles in rubber–Si systems with the contrast variation small-angle neutron scattering (SANS) method. We have investigated the polymer layers absorbed on carbon black (CB) particles in rubber–CB systems with contrast variation SANS method. The scattering intensities of specimens swollen by the solvents having various scattering length densities were measured. The contrast variation SANS for the specimens yielded partial scattering functions: the scattering function for polymer–polymer correlation SPP(q), the scattering function for CB–CB correlation SCC(q), and the scattering function for polymer–CB correlation SPC(q). The analyses of SCC(q) explored the structures of the aggregates formed by CB particles. The analyses of SPC(q) and SCC(q) clarified the existence of dense polymer layers around CB aggregates. Several characteristic parameters are estimated from the analyses, such as the size of aggregates, the thickness of layers, and the volume fractions of polymer layers and matrix. We found that the adsorption layer around CB aggregates is thicker than that around Si aggregates in rubber–Si systems.

Contrast Variation SANS Study of DNA Packaging in Bacteriophage λ

The elegant physical structure of viruses has attracted wide-spread interests from structural biologists, biophysicists, and mathematicians. While the protein capsids of viruses posses the nearly universal quasi-equivalence of icosahedral symmetry, the configuration of viral DNA/RNA genome appears less structured and is still poorly understood. Here we report a contrast variation small angle neutron scattering (SANS) study of bacteriophage λ to probe the spatial organization of its dsDNA genome. Contrast variation SANS takes advantage of the different scattering lengths of protein and DNA, and can experimentally match the protein contrast so as to measure the DNA structure alone. Together with the known structure of the protein capsid, SANS data at different H/D ratios offer the opportunity for extensive structural modeling. Furthermore, knowledge of DNA configuration in bacteriophage λ impinges directly on the physics of pressurized DNA packaging known to drive the initial DNA ejection when infecting bacteria. Multivalent cations were used to modulate the internal DNA pressure, and the induced structural changes were measured by contrast variation SANS. We compare the various DNA packaging models proposed in the literature and discuss their consistencies and discrepancies with experimental data.

コントラスト変調小角中性子散乱法によるカーボンブラック充てん系の構造解析

The polymer layers adsorbed on carbon black (CB) aggregates in rubber/CB systems have been investigated with contrast variation small-angle neutron scattering (SANS) method. Specimens were swollen by toluene/deuterated toluene solvents having various scattering length densities and their scattering intensities were measured with SANS. The contrast variation SANS for the specimens yielded partial scattering functions: the scattering function for polymer-polymer correlation Spp(q), the scattering function for CB- CB correlation Scc(q), and the scattering function for polymer- CB correlation Spc(q). The analyses of the partial scattering functions explored the existence of dense polymer layers around CB aggregates. Several characteristic parameters are estimated from the analyses, such as the size of aggregates, the thickness of layers, and the volume fractions of polymer of layers and matrix.

Mechanically Interlocked Structure of Polyrotaxane Investigated by Contrast Variation Small-Angle Neutron Scattering

ADVERTISEMENT RETURN TO ISSUEPREVNoteNEXTMechanically Interlocked Structure of Polyrotaxane Investigated by Contrast Variation Small-Angle Neutron ScatteringKoichi Mayumi†*, Hitoshi Endo‡*, Noboru Osaka‡, Hideaki Yokoyama†, Michihiro Nagao§⊥, Mitsuhiro Shibayama‡, and Kohzo Ito†View Author Information† Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan‡ Institute for Solid State Physics, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan§ NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-6102⊥ Cyclotron Facility, Indiana University, Bloomington, Indiana 47408-1398*Corresponding authors. E-mail: [email protected] (H.E.); [email protected] (K.M.).Cite this: Macromolecules 2009, 42, 16, 6327–6329Publication Date (Web):July 7, 2009Publication History Received12 May 2009Revised17 June 2009Published online7 July 2009Published inissue 25 August 2009https://doi.org/10.1021/ma9010318Copyright © 2009 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views927Altmetric-Citations23LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (1 MB) Get e-AlertsSUBJECTS:Cadmium sulfide,Molecular structure,Organic reactions,Polymers,Scattering Get e-Alerts

Structure Analyses of Swollen Rubber-Filler Systems by Using Contrast Variation SANS

The polymer layers adsorbed on silica particles in rubber−silica systems have been investigated with the contrast variation small-angle neutron scattering (SANS) method. The scattering intensities of specimens swollen by solvents with various scattering length densities were measured. The contrast variation SANS for the specimens yielded partial scattering functions: the scattering function for polymer−polymer correlation SPP(q), the scattering function for silica−silica correlation SSS(q), and the scattering function for polymer−silica correlation SPS(q). The analyses of SSS(q) explored the hierarchical structures formed by silica particles. The analyses of SPS(q) and SSS(q) clarified the existence of dense polymer layers around silica aggregates. Several characteristic parameters are estimated from the analyses, such as the size of aggregates, the thickness of layers, the volume fractions of polymer of layers and matrix, and the correlation length of the matrix network. The contrast variation SANS is found to be a powerful tool for the analyses of the structures of the rubber-filler systems.

Structure of Nanocomposite Hydrogel Investigated by Means of Contrast Variation Small-Angle Neutron Scattering

The structure of poly(N-isopropylacrylamide)−clay nanocomposite gels (NC gel) is investigated. The sophisticated contrast variation small-angle neutron scattering technique leads to obtain the partial scattering functions of each component quantitatively. The extracted partial scattering functions of clay, polymer, and the polymer−clay cross-term are analyzed in detail, and the selective interaction between clay and polymer is revealed. On the basis of these structural observations, it is confirmed that the clay nanoparticles serve as 2-dimensional cross-linkers.

Study on Multi-Component Systems by Means of Contrast Variation Small Angle Neutron Scattering

Contrast variation small angle neutron scattering method is reviewed. Due to overlapping of the scattering signals from each component, the data analyses of scattering patterns from multicomponent systems are attended with much difficulty. We can overcome this problem with the aid of contrast variation.In this manuscript, experimental procedure of the contrast variation small angle neutron scattering as well as a theoretical basis for understanding of the partial scattering functions (both self-terms and cross-terms) are briefly described.

Structure analyses of rubber-filler systems by contrast variation SANS

The network structures in rubber containing silica particles have investigated with contrast variation small-angle neutron scattering (SANS) method. The contrast variation SANS for the rubber specimens swollen by the solvents having various scattering length densities yielded partial scattering functions: the scattering function for polymer-polymer correlation Spp (q), the scattering function for silica-silica correlation Sss(q), and the scattering function for polymer-silica correlation SPS(q). The analyses of the partial scattering functions explored the following features:(1) Silica particles form aggregates consisting of several silica particles, and (2) there are relatively dense polymer layers around silica aggregates. Several characteristic parameters are estimated from the analyses, such as the size of aggregates, the thickness of layers, the volume fractions of polymer of layers and matrix, and the correlation length of the matrix network. This result suggests that the contrast variation SANS is a powerful tool of the analyses of the structures of the rubber-filler systems.

An analysis of a polymer additive for calcium carbonate crystallization - a small-angle neutron scattering investigation by applying contrast variation

The role of the double-hydrophilic block copolymers (poly(ethylene glycol)-block-poly(methacrylic acid)) on the morphogenesis of calcium carbonate (CaCO3) was studied by applying contrast variation small-angle neutron scattering (SANS). The scattering function for ternary systems can be expressed by only partial scattering functions of the single species, as derived on the assumption of incompressibility. We demonstrate the feasibility of this formula by means of contrast variation SANS, and the decomposed partial scattering functions give their detailed information. Especially the partial scattering function of polymer shows a Q −2.7 monotonic slope at low Q (0.002 Å &lt; Q &lt; 0.02 Å; Q is the modulus of the scattering vector), which is a clear evidence that the distribution of the polymer in CaCO3 has a mass fractal dimension. This result is confirmed by time-resolved SANS experiments with CaCO3 contrast, where a Q −2.5 slope was observed at the early stage of the reaction in the same Q range.

Microstructural Analysis of Activated Carbons Prepared from Paper Mill Sludge by SANS and BET

Small-angle neutron scattering (SANS) and N2-BET analysis were used to characterize the microstructure of a series of activated carbons produced from paper mill sludge using ZnCl2. N2-BET and SANS data indicate that the micro- and mesoporous surface areas of the carbons increase with the concentration of ZnCl2 used in their preparation. Contrast variation SANS studies demonstrate the existence of two different phases, a zinc-rich particle phase and a bulk carbon phase with nanopores. Both phases are largely accessible to the solvent. The size and morphology of the pores and inclusions were determined from the SANS data. The pores are found to be roughly rodlike. The radii and volumes of the pores increase with increasing the amount of activating agent (ZnCl2) used for the production of the carbons. On the basis of SANS results, we propose a conceptual model describing structural characteristics of the produced carbons.

Contrast Variation Small-Angle Neutron Scattering Study of the Structure of Block Copolymer Micelles in a Slightly Selective Solvent at Semidilute Concentrations

The structure of micelles of an asymmetric polystyrene−polyisoprene (PS−PI) diblock copolymer has been studied in di-n-butyl phthalate (DBP), which is a slightly selective solvent for PS. The polymer has a molecular weight of 11 500 for the fully deuterated d-PS block and 48 500 for the PI block. Contrast variation SANS using mixtures of protonated and deuterated solvent and a polymer volume fraction of 18% at 10 °C were performed to get detailed information on the structure of the micelles. An additional contrast was obtained by performing a small-angle X-ray scattering measurement on a sample in protonated DBP. It was found that micelles are formed with an anisometric PI-rich core surrounded by dissolved d-PS chains. The data were analyzed using model form factors of micelles with, respectively, cylindrical and ellipsoidal cores. It was necessary to include a term to describe the concentration fluctuations within the swollen PI cores. The particle interference effects originating from the high volume fr...