Near-field scattering techniques: Novel instrumentation and results from time and spatially resolved investigations of soft matter systems

Recently the investigation of non-stationary systems exhibiting spatial and dynamic heterogeneities has propelled the development of innovative optical techniques providing the missing link between the scattering and imaging approaches. The novel techniques are characterized by the fact that the scattered radiation is measured close to the sample. They allow to recover information on the structure and dynamics of the system under investigation equivalent to that available with scattering techniques, with the great advantage that they simultaneously allow to achieve a local characterization of the sample, which is lost in traditional scattering measurements.     

Characteristics of AOT Microemulsion Structure: a Small Angle X-ray Scattering Study

The structure of micelles has attracted renewed attention during the past decade years due to the widespread use of microemulsions in technology1 and life science1,2. To obtain information of the micellar structure, using X-ray scattering (SAXS) whose wavelength is close to the size of the micellar aggregates is one of the most direct method3-5 and SAXS has been proved to be very sensitive for the change of micellar composition6,7. SAXS experiments have been carried out to compare the st…     

Peptide meets membrane: Investigating peptide-lipid interactions using small-angle scattering techniques

Peptide–lipid interactions play an important role in defining the mode of action of drugs and the molecular mechanism associated with many diseases. Model membranes consisting of simple lipid mixtures mimicking real cell membranes can provide insight into the structural and dynamic aspects associated with these interactions. Small-angle scattering techniques based on X-rays and neutrons (SAXS/SANS) allow in situ determination of peptide partition and structural changes in lipid bilayers in vesicles with relatively high resolution between 1-100 nm. With advanced instrumentation, time-resolved SANS/SAXS can be used to track equilibrium and nonequilibrium processes such as lipid transport and morphological transitions to time scales down to a millisecond. In this review, we provide an overview of recent advances in the understanding of complex peptide–lipid membrane interactions using SAXS/SANS methods and model lipid membrane unilamellar vesicles. Particular attention will be given to the data analysis, possible pitfalls, and how to extract quantitative information using these techniques.     

On Aging of Acid-Catalyzed Silica Sols—A Dynamic Light Scattering Study

Dynamic light scattering experiments in acid-catalyzed silica sols are discussed. It is shown that in spite of limited parameter accuracy and limited absolute knowledge of the particle sizes, the scattering data from various experiments are comparable with one another and give information about structural differences. Measurements at various angles indicate changes between non-spherical and nearly spherical particles and allow the estimation of gelling times before gelation.     

New sights into the electrochemical interface provided by in situ X-ray absorption fine structure and surface X-ray scattering

Various important processes, such as electron transfer reactions, adsorption/desorption, solvation/desolvation, and formation/cleavage of chemical bonds, take place at electrolyte/electrode interfaces during electrocatalytic reactions. Those processes have been understood on the basis of changes in the surface composition, atomic arrangement, and molecular and electronic structures of the interfaces by using various in situ analysis techniques. To date, in situ analysis and observation of those interfacial processes at an ideal single-crystal surface are indispensable not only for fundamental understanding of the reaction mechanism but also for rational design of the highly efficient and durable electrocatalytic materials. Here, historical and recent progress of in situ studies on electrocatalytic reactions is briefly reviewed with a focus on two major techniques, X-ray absorption fine structure and surface X-ray scattering.     

Online SAXS investigations of polymeric hollow fibre membranes

Polymeric membranes are used in industrial and analytical separation techniques. In this study small-angle X-ray scattering (SAXS) with synchrotron radiation has been applied for in-situ characterisation during formation of polymeric membranes. The spinning of a polyetherimide (PEI) hollow fibre membrane was chosen for investigation of dynamic aggregation processes during membrane formation, because it allows the measurement of the dynamic equilibrium at different distances from the spinning nozzle. With this system it is possible to resolve structural changes in the nm-size range which occur during membrane formation on the time-scale of milliseconds. Integral structural parameters, like radius of gyration and pair-distance distribution, were determined. Depending on the chosen spinning parameters, e.g. the flow ratio between polymer solution and coagulant water, significant changes in the scattering curves have been observed. The data are correlated with the distance from the spinning nozzle in order to get information about the kinetics of membrane formation which has fundamental influence on structure and properties of the membrane.     

Light,Small Angle Neutron and X-Ray Scattering from Gels

This paper gives two examples of experiments that demonstrate the power of small angle scattering techniques in the study of swollen polymer networks. First, it is shown how the partly ergodic character of these systems is directly detected by neutron spin echo experiments. The observed total field correlation function of the intensity scattered from a neutral gel allows the ergodic contribution to be directly distinguished from the non ergodic part, at values of transfer wave vector q that lie well beyond the range of dynamic light scattering. The results can be compared with those obtained at much lower q from visible light scattering. Second, a recent application of small angle X-ray (SAXS) and neutron (SANS) scattering is described for a polyelectrolyte molecule, DNA, in semi-dilute solutions under near-physiological conditions. For these observations, the divalent ion normally present, calcium, is replaced by an equivalent ion, strontium. The comparison between SANS and SAXS yields a quantitative picture of the cloud of divalent counter-ions around the central DNA core. At physiological conditions, the cloud is thinner than that predicted on the basis of the Debye screening length but thicker than if the counter-ions were condensed on the DNA chain.     

Elucidation of the Structure of Organic Solutions in Solvent Extraction by Combining Molecular Dynamics and X‐ray Scattering

Knowledge of the supramolecular structure of the organic phase containing amphiphilic ligand molecules is mandatory for full comprehension of ionic separation during solvent extraction. Existing structural models are based on simple geometric aggregates, but no consensus exists on the interaction potentials. Herein, we show that molecular dynamics crossed with scattering techniques offers key insight into the complex fluid involving weak interactions without any long‐range ordering. Two systems containing mono‐ or diamide extractants in heptane and contacted with an aqueous phase were selected as examples to demonstrate the advantages of coupling the two approaches for furthering fundamental studies on solvent extraction.     

Cure temperature influence on natural rubber—A small angle X‐ray scattering study

To analyze the natural rubber behavior during vulcanization under different cure treatments, an experimental investigation using small angle X‐ray scattering was performed. To achieve this, a set of samples were prepared using sulfur and N‐t‐butyl‐2‐benzothiazole sulfenamide as accelerator and then cured at temperatures between 403 and 463 K reaching their optimum mechanical properties considering rheometer tests. The crosslink density of the samples was evaluated by means of the swelling technique in solvent. In the usual Lorentz corrected representation of the X‐ray scattered intensity, a maximum was observed in the plots corresponding to the cured samples, revealing a highly correlated structure. This maximum shifted toward higher values of the scattering vector when the cure temperature of the samples increased. This behavior is discussed in terms of the crosslinks type present in the vulcanized rubber network at different cure temperatures. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2966–2971, 2007     

Improving the picture of atomic structure in nonoriented polymer domains using the pair distribution function: A study of polyamide 6

Investigations of the atomic structures within polyamides started over 80 years ago and continue today. These weakly ordered materials diffract X-rays poorly and typically require postprocessing to obtain idealized samples for structural studies. An important goal remains to develop techniques to study the local structure in its natural state, with atomic resolution, and with sensitivity to subtle changes due to synthesis conditions or other technologically relevant processing procedures. Here, we compare the structures of as-produced, nonoriented polyamide 6 ([C₆H₁₁NO] _n) from both hydrolytic and anionic processes. A total scattering pair distribution function approach is used to elucidate information about the atomic bonding, molecular conformation, chain packing, crystallite size, and ratio of ordered to disordered domain content. The results are compared with those from standard analytical methods.     

Ultra-small-angle X-ray and neutron scattering study of colloidal dispersions

The ultra-small-angle X-ray and neutron scattering techniques are useful techniques for the investigation of colloidal systems. The very high small-angle resolution of these scattering techniques has provided important and novel information to elucidate the formation mechanism of colloidal crystals. The Bonse–Hart optical system is expected to become a standard tool for investigating mesoscopic structures.     

In-Situ/Operando X-ray Characterization of Metal Hydrides

In this article, the capabilities of soft and hard X-ray techniques, including X-ray absorption (XAS), soft X-ray emission spectroscopy (XES), resonant inelastic soft X-ray scattering (RIXS), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD), and their application to solid-state hydrogen storage materials are presented. These characterization tools are indispensable for interrogating hydrogen storage materials at the relevant length scales of fundamental interest, which range from the micron scale to nanometer dimensions. Since nanostructuring is now well established as an avenue to improve the thermodynamics and kinetics of hydrogen release and uptake, due to properties such as reduced mean free paths of transport and increased surface-to-volume ratio, it becomes of critical importance to explicitly identify structure-property relationships on the nanometer scale. X-ray diffraction and spectroscopy are effective tools for probing size-, shape-, and structure-dependent material properties at the nanoscale. This article also discusses the recent development of in-situ soft X-ray spectroscopy cells, which enable investigation of critical solid/liquid or solid/gas interfaces under more practical conditions. These unique tools are providing a window into the thermodynamics and kinetics of hydrogenation and dehydrogenation reactions and informing a quantitative understanding of the fundamental energetics of hydrogen storage processes at the microscopic level. In particular, in-situ soft X-ray spectroscopies can be utilized to probe the formation of intermediate species, byproducts, as well as the changes in morphology and effect of additives, which all can greatly affect the hydrogen storage capacity, kinetics, thermodynamics, and reversibility. A few examples using soft X-ray spectroscopies to study these materials are discussed to demonstrate how these powerful characterization tools could be helpful to further understand the hydrogen storage systems.     

X-ray Photon Correlation Spectroscopy of Dynamics in Thermosensitive Gels

Summary : Temperature-sensitive hydrogels undergo a volume phase transition (VPT) when heated above a critical temperature T_c. For the poly(N-isopropyl acrylamide) (PNIPA)-water system, T_c. = 34 °C. Below T_c the gels are transparent and highly swollen. On warming above T_c they promptly turn white and start to deswell. The rate of deswelling, however, can be orders of magnitude slower than that of swelling below T_c. The unstable intermediate structure above T_c, can retain the solvent and conserve the sample volume for may days, even with millimetre-sized samples. Light scattering observations of the internal structure of these gels above T_c are precluded by their strong turbidity. Small angle X-ray scattering measurements (SAXS), on the other hand, are less subject to multiple scattering as X-rays penetrate more easily into the bulk material. Conventional (incoherent) SAXS observations reveal intense scattering from smooth internal water-polymer interfaces with an estimated surface area of about 7 m²/g in the swollen gel. The dynamics in the off-equilibrium high temperature state, investigated by X-ray photon correlation spectroscopy (XPCS), displays a relaxation rate that is linearly proportional to the wavevector q, rather than to q² as in diffusion processes. The physical origin of this relaxation is consistent with jamming, a phenomenon that is common in other disordered systems.     

X‐Ray Scattering and Imaging Studies of Electrode Structure and Dynamics

We will review structures and dynamics of electrode interfaces studied in situ using x‐ray scattering and imaging techniques. The examples cover single‐crystal and nanocrystal structures relevant to electrocatalytic activities, anodic oxidation and corrosion, aqueous dissolution reactions, surface reconstructions, and surface modifications by under potential deposition. The x‐ray techniques include the widely used traditional surface x‐ray scattering, such as crystal truncation rods and x‐ray reflectivity, as well as recently developed resonance surface scattering, coherent surface x‐ray photon correlation spectroscopy, coherent x‐ray Bragg diffraction imaging, and surface ptychography. Results relevant to various electrochemical phenomena will be highlighted.     

An In Situ Small-Angle X-Ray Scattering Study of Propylene-Butene and Propylene-Ethylene Random Copolymers during Heating Process

Summary: The micro-structure evolution of isotactic polypropylene-1-butene (iPPBu) and polypropylene-ethylene (iPPEt) random copolymers with 4 mol% of 1-butene and ethylene was respectively investigated by differential scanning calorimetry (DSC) and in-situ small angle X-ray scattering (SAXS) techniques during heating process. The signal of melting enthalpy of iPPBu disappears a little earlier than that of iPPEt, which keeps consistent with the decay trend of scattering intensity during the late period of melting process. However, the SAXS data further show that the crystal thickness of iPPBu is a little larger than that of iPPEt during heating process. It is suggested that the melting behaviors of such copolymers depend on not only the lamellar thickness but also the crystal stability.     

Stable DOPG/Glycyrrhizin Vesicles with a Wide Range of Mixing Ratios: Structure and Stability as Seen by Scattering Experiments and Cryo-TEM

Phosphatidylglycerols represent a large share of the lipids in the plasmamembrane of procaryotes. Therefore, this study investigates the role of charged lipids in the plasma membrane with respect to the interaction of the antiviral saponin glycyrrhizin with such membranes. Glycyrrhizin is a natural triterpenic-based surfactant found in licorice. Vesicles made of 1,2-dioleoyl-sn-glycero-3-phospho-rac-(1’-glycerol) (DOPG)/glycyrrhizin are characterized by small-angle scattering with neutrons and X-rays (SANS and SAXS). Small-angle scattering data are first evaluated by the model-independent modified Kratky–Porod method and afterwards fitted by a model describing the shape of small unilamellar vesicles (SUV) with an internal head-tail contrast. Complete miscibility of DOPG and glycyrrhizin was revealed even at a ratio of lipid:saponin of 1:1. Additional information about the chain-chain correlation distance of the lipid/saponin mixtures in the SUV structures is obtained from wide-angle X-ray scattering (WAXS).     

Relationships between nanostructure and thermomechanical properties in poly(vinyl alcohol)/montmorillonite nanocomposite with an entrapped polyelectrolyte

Poly(vinyl alcohol)/montmorillonite (PVA/MOM) hydrogels containing coacervated microparticles of sulfonated polyester (PES) were prepared by direct mixture of the components in water. The system was characterized by using differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), and dynamical mechanical analysis (DMA). The influence of PES and MOM on the microstructure of the nanocomposite hydrogels was established. The presence of PES causes a significant change on the crystallinity of PVA. Furthermore, the presence of MOM leads to a hierarchical nanostructure that also contributes to change the crystallinity of PVA. The results of structural investigation are correlated with the mechanical properties of the composites obtained by DMA. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2618–2629, 2008     

Scattering from polymer-like micelles

Polymer-like micelles are analogs to polymer solutions and provide an exciting class of materials for both applications and fundamental understanding of polyelectrolyte systems. Small angle neutron and X-ray scattering have been key to the characterization of these materials from the first observations of linear micelle growth. As new materials are developed, these techniques continue to be utilized and combined with other analytical tools to characterize the length and time scales of polymer-like micelle behavior. Recent reports on the use of small-angle scattering to characterize polymer-like and wormlike micelles are reviewed, with focus on new materials, improvements in analytical approaches and anisotropic structures.     

A small angle neutron scattering and electrochemical impedance spectroscopy study of the nanostructure of the iron chalcogenide glass ion-selective electrode

This paper presents a preliminary structural and interfacial study of the iron chalcogenide glass [i.e., Fe_x(Ge₂₈Sb₁₂Se₆₀)_100−x] ion-selective electrode (ISE) using small angle neutron scattering (SANS) and electrochemical impedance spectroscopy (EIS). SANS detected variations in the neutron scattering as a function of iron content in the chalcogenide glass. Furthermore, a change in the chalcogenide glass structure was observed at elevated iron dopant levels. Conversely, EIS was used to show that the iron chalcogenide membrane comprises various time constants, and the interfacial charge transfer reaction depends on the membrane iron content. Equivalent circuit modeling revealed that the charge transfer resistance decreases at elevated iron levels, and this may be related to the presence of iron defects in the glass. It is proposed that the iron chalcogenide membrane comprises an iron nanostructural network embedded in the amorphous matrix, and this directly influences the electrical conductivity and concomitant electrochemical reactivity of the glass.