Small-angle X-ray Measurements Research Articles

Crystallization behavior of polyethylene on silicon wafers in solution casting processes traced by time-resolved measurements of synchrotron grazing-incidence small-angle and wide-angle X-ray scattering

Crystallization behavior of polyethylene (PE) on silicon wafers in solution casting processes has been successfully traced by time-resolved grazing-incidence small-angle and wide-angle X-ray scattering (GISWAXS) measurements utilizing synchrotron radiation. A p-xylene solution of PE kept at ca. 343 K was dropped on a silicon wafer at ca. 298 K. While the p-xylene evaporated naturally from the dropped solution sample, PE chains crystallized to be a thin film. Raman spectral measurements were performed simultaneously with the GISWAXS measurements to evaluate quantitatively the p-xylene the dropped solution contained. Grazing-incidence wide-angle X-ray scattering (GIWAXS) patterns indicated nucleation and crystal growth in the dropped solution and the following as-cast film. GIWAXS and Raman spectral data revealed that crystallization of PE was enhanced after complete evaporation of the p-xylene from the dropped solution. The [110] and [200] directions of the orthorhombic PE crystal became relatively parallel to the wafer surface with time, which implied that the flat-on lamellae with respect to the wafer surface were mainly formed in the as-cast film. On the other hand, grazing-incidence small-angle X-ray scattering (GISAXS) patterns implied formation of isolated lamellae in the dropped solution. The lamellae and amorphous might alternatively be stacked in the preferred direction perpendicular to the wafer surface. The synchrotron GISWAXS experimental method could be applied for kinetic study on hierarchical structure of polymer thin films.

Structural evolution process of isotactic polypropylene in the isothermal crystallization from the melt

The melt-isothermal crystallization behaviour has been investigated for isotactic polypropylene (iPP) by means of time-resolved simultaneous measurements of small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) using synchrotron radiation source in SPring-8. The time-resolved Fourier-transform infrared spectral (FTIR) measurements were also performed to clarify the formation process of helices. The SAXS data were analyzed on the basis of Guinier (isolated domains) and Debye-Bueche (correlated domains) theories and correlation function (stacked lamellae). The results were combined with the FTIR data, allowing us to draw the concrete structural evolution process including the formation of regular helices and their growth, the correlation of higher density domains consisting of these helices, and the increment of correlation between the neighbouring lamellae to build up the stacked lamellar structure of higher crystallinity.

Relation between local necking and cavitation during high-temperature tensile deformation of polycrystalline pure aluminum

For polycrystalline aluminum with grain size of 170 and 346μm, tensile deformation was carried out at a true strain rate of 1×10−2/s and a temperature of 553K (=0.59Tm, Tm: melting temperature in K). Onset and progress of local necking during the deformation were investigated by measurements of small-angle X-ray scattering (SAXS) from a viewpoint of cavity formation on grain boundaries. The cavitation was observed in the change of the SAXS intensities as a function of local strain along the gauge part of specimen. The intensities increase rather slowly during the beginning uniform deformation. However, it increases rapidly in the gauge part where the local necking has occurred. The degree of cavitation is found to be more remarkable for a specimen with smaller grain size. Cavity size and size distribution are evaluated from the SAXS profiles. The local necking phenomenon is discussed from a viewpoint of cavitation.

Influence of third monomer on the crystal phase transition behavior of ethylene–tetrafluoroethylene copolymer

Crystal phase transition between the low- and high-temperature phases has been investigated for ethylene (E)–tetrafluoroethylene (TFE) alternating copolymer (ETFE) containing the third monomeric species by the temperature dependent measurements of wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) and differential scanning calorimetry. Nonafluoro-1-hexene (NFH) and hexafluoropropylene (HFP) were chosen as the third monomers, where they are different in the side-branch length, –(CF2)3CF3 and –CF3, respectively. In the case of E/TFE/NFH copolymer (ET–C4F9), the crystal phase transition temperature of the original ETFE two-components copolymer was not very much affected by the existence of NFH in the range of NFH content from 0.7 to 3mol%. Contrarily, the crystal phase transition temperature of E/TFE/HFP copolymer (ET–CF3) was found to decrease drastically with increasing HFP content. The melting temperature and the higher-order structure were also affected sensitively depending on the HFP content. This difference in phase transition behavior between ET–C4F9 and ET–CF3 copolymers is reasonably interpreted as follows: the short side groups (–CF3) of HFP monomeric unit are included in the crystal lattice of E/TFE chains and the unit cell is expanded gradually with an increment of the HFP content, resulting in the decrease in phase transition point because of easier thermal motion of the chains. On the other hand, the long side groups [–(CF2)3CF3] of NFH monomeric units are excluded out of the crystal lattice and located on the lamellar surfaces or in the amorphous region and do not affect very much the phase transition temperature even when the NFH content is increased. In association with such a change in crystal structure, the long period of stacked lamellar structure was found to decrease remarkably in the case of NFH, whereas it does not change very much for HFP, consistent with the interpretation of the above-mentioned WAXD data.

Unbinding Transition in Lipid Multibilayers Induced by Copper(II) Ions

We describe our observations on an unbinding transition in a multilamellar dispersion of phosphatidylcholine (PC) vesicles induced by copper(II) ions. The small-angle X-ray measurements clearly show that the increasing amount of CuCl2 in the millimolar concentration range continuously increases the amount of the unbound bilayers in the gel phase. Moreover, this phenomenon becomes more pronounced when the samples are heated above the so-called pretransition temperature between the gel and the ripple gel phase. The proposed reason for the latter is the increased repulsive electrostatic interaction due to the appearance of the surface modulation in the ripple gel phase. The observed effects reveal a new aspect of the unbinding phenomena since only the transition induced by the steric repulsion due to the layer fluctuations has been considered so far. Here, we show that the unbinding can also be triggered by the change in the electrostatic interactions. These findings are connected to the physical basis of the crucial role of copper(II) ions in biological processes such as neurodegenerative diseases and cell evolution.

Estimation of pore structures in carbon fibers prepared from polymer blends during carbonization by small-angle X-ray scattering

We previously investigated the pore structure in carbon fibers prepared from polymer blends consisting of carbon precursor resin and pore forming resin by measurements of small-angle X-ray scattering (SAXS), and reported the heat treatment temperature (HTT) dependence of the pore structures elsewhere.In this paper, a least-square-fitting analysis of theoretical scattering intensities for experimental intensities was introduced in order to get the results with higher reliability. We also measured SAXS intensity of the polymer blend fiber without heat treatment and carbonization to investigate the structure of the pore forming resin in the fiber. We considered the structural change of the pore forming resin and the formed pores with heat treatment and carbonization.

Structural Correlation between Crystal Lattice and Lamellar Morphology in the Phase Transitions of Uniaxially Oriented Syndiotactic Polystyrene (δ and δe Forms) As Revealed by Simultaneous Measurements of Wide-Angle and Small-Angle X-ray Scatterings

The simultaneous measurement of wide-angle (WAXS) and small-angle X-ray scattering (SAXS) patterns has been made successfully for the first time for the uniaxially oriented δ (filled clathrate) and δe (emptied clathrate) forms during the heating process. The basic idea behind these measurements is to clarify the correlation between the crystal structure change and the morphological change of the stacked lamella. At room temperature the δ and δe forms showed a two-point scattering pattern, indicating the stacked lamellar structure. However, in the δe form the two-point scattering pattern was completely masked by strong diffused scattering because of the empty cavities in the crystal lattice due to the removal of solvent molecules. WAXS and SAXS results revealed that the δ to γ phase transition occurs smoothly without disturbing the stacked lamellar structure very much. On the other hand, a major reorganization in the stacked lamellar structure was observed in the case of δe to γ transition through a disord...

Apparatus for the simultaneous measurement of the X-ray absorption factor developed for a small-angle X-ray scattering beamline

A novel apparatus has been developed that enables the simultaneous determination of the absorption factor during measurement of small-angle X-ray scattering (SAXS) intensities of a sample. It was designed especially for the use of relatively low-energy X-rays at SAXS beamlines of synchrotron facilities. The X-ray intensity of transmittance is measured by a silicon PIN photodiode, which is implanted in a direct beamstop set in a vacuum chamber. Since the assembly transmits an attenuated direct beam to a detector during the scattering measurement, a zero-angle position can be monitored without additional operation. It was confirmed that the linearity between the signal from the photodiode and the intensity of X-rays is good and the photodiode is applicable for the desired purpose. For a performance test, the absorption factors of a supercritical fluid were measured with a wide density range.

The effects of thermal annealing on commercial Nafion ® membranes

The effect of thermal annealing as a pretreatment procedure for Nafion ® membranes was investigated. Commercial membranes with different thicknesses and ages (all melt extruded films) were considered. After a short heat treatment at 165 °C, the proton conductivity, water permeability, equilibrium water sorption, and self-diffusion coefficient of water and protons increased in all films, with the greatest improvements occurring in thin films (<50 μm). Wide-angle X-ray measurements showed that the annealing procedure decreases the crystallinity of thick films and increases the crystallinity of thin films, in general. Small-angle X-ray measurements showed that annealing may alter the distribution of water within the films. Thermal annealing appears to ‘normalize’ the transport properties of different thicknesses and batches of Nafion ®, reducing the differences in values of measured transport properties between thin and thick membranes.

Structure Evolution during Cyclic Deformation of an Elastic Propylene-Based Ethylene−Propylene Copolymer

In-situ structural evolution during uniaxial extension and subsequent retraction of a thermoplastic elastomer (TPE) based on propylene-dominant ethylene−propylene (EP) copolymer was studied. Combined measurements of time-resolved wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) as well as stress−strain curves revealed molecular mechanism responsible for the elastic behavior. During the first cycle of deformation, a fraction of the crystals was destroyed, while the rest was reoriented. At strains larger than 1.0, strain-induced α-crystals in the lamellar form took place, resulting in the creation of a network with well-oriented lamellae having their normals parallel to the stretching direction. With the increase of strain, more crystals were induced, forming an enhanced network with strain-hardening behavior. During retraction and even after complete relaxation to zero stress, the majority of the strain-induced crystalline network remains in tact as being “permanent set”, where l...

Organic−Inorganic Hybrid Liquid Crystals: Thermotropic Mesophases Formed by Hybridization of Liquid-Crystalline Phosphates and Monodispersed α-Fe2O3 Particles

A novel organic-inorganic hybrid thermotropic liquid crystal (LC) is developed by the hybridization of an organic phosphate having a mesogenic core and monodispersed alpha-Fe2O3 particles with different shapes through the specific adsorption of the phosphate group to the surfaces parallel to the c-axis of the alpha-Fe2O3. The hybrid LC shows thermotropic nematic or cubic liquid-crystallinity in wide ranges of temperatures. Variable-temperature small-angle X-ray measurements reveal that the spontaneous formation of periodic structure by the hybridization induces the thermotropic liquid crystallinity. This technique would lead development of novel types of dynamic functional materials with multi-responsiveness to magnetic and electric fields.

Structural deformation behavior of isotactic polypropylene with different molecular characteristics during hot drawing process

Structural evolution in hot drawing process of isotactic polypropylene (iPP) films with different molecular weight distribution (MWD) and isotacticity (IT) was investigated by in situ time-resolved measurements of synchrotron-sourced wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS). Any significant difference was not recognized among different molecular characteristics as for the changes in the WAXD patterns, indicating that the deformation behavior viewed at the crystal lattice scale was almost the same among these samples. On the other hand, the deformation behavior of lamellar stacking structure was found to be significantly dependent on the molecular characteristics of the sample used. For iPP sample with narrower MWD and higher IT, only the lamellar stacking structure with c-axis crystallites oriented along the drawing direction was detected at the deformation stage after necking, but the oriented fibrillar structure was observed in addition to the lamellar stacking structure for the iPP sample with broader MWD and IT distribution. The structural deformation models were presented for both the samples with different molecular characteristics, and these models were reasonably related with the difference in the stress–strain curve.

Interpretation of small angle X-ray measurements guided by molecular dynamics simulations of lipid bilayers

Reconstruction and interpretation of lipid bilayer structure from X-ray scattering often rely on assumptions regarding the molecular distributions across the bilayer. It is usually assumed that changes in head–head spacings across the bilayer, as measured from electron density profiles, equal the variations in hydrocarbon thicknesses. One can then determine the structure of a bilayer by comparison to the known structure of a lipid with the same headgroup. Here we examine this procedure using simulated electron density profiles for the benchmark lipids DMPC and DPPC. We compare simulation and experiment in both real and Fourier space to address two main aspects: (i) the measurement of head–head spacings from relative electron density profiles, and (ii) the determination of the absolute scale for these profiles. We find supporting evidence for the experimental procedure, thus explaining the robustness and consistency of experimental structural results derived from electron density profiles. However, we also expose potential pitfalls in the Fourier reconstruction that are due to the limited number of scattering peaks. Volumetric analysis of simulated bilayers allows us to propose an improved, yet simple method for scale determination. In this way we are able to remove some of the restrictions imposed by limited scattering data in constructing reliable electron density profiles.

Organic-inorganic hybrid liquid crystals: hybridization of calamitic liquid-crystalline amines with monodispersed anisotropic TiO2 nanoparticles.

A novel organic-inorganic hybrid thermotropic liquid crystal (LC) is developed by the hybridization of an organic amine with a mesogenic core and an acicular anisotropic TiO2 particle through the adsorption of the amino group to the surfaces of the TiO2. The hybrid LC shows nematic phases in wide ranges of temperatures. Variable-temperature small-angle X-ray measurements reveal that the formation of the one-dimensional nematic order of the acicular particles on a submicrometer scale induces thermotropic liquid crystallinity. This technique would lead to induction of dynamic functions in inorganic particles.

Structural changes in non-isothermal crystallization process of melt-cooled polyoxymethylene[II] evolution of lamellar stacking structure derived from SAXS and WAXS data analysis

Structural change occurring in the cooling process of polyoxymethylene from the molten state has been investigated by carrying out the temperature dependent measurements of small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS). In the SAXS experiment the generation of lamellar stacking structure with long period of ca. 14 nm was detected at first and then the new lamellae were inserted in between the already-existing lamellae to give the long period of 7 nm below 140 °C. The SAXS data were analyzed on the basis of lamellar insertion model by taking into account the second kind of paracrystalline disorder about the lamellar stacking mode. The thus obtained results were combined with the previously published infrared spectral data, and the structural change was deduced concretely. The generation of taut tie chains passing through the adjacent lamellae was proposed, which could reasonably explain the observation of infrared bands characteristic of extended-chain-crystal-like morphology.

Influence of thermal aging on density fluctuations in oxide glasses measured by small-angle X-ray scattering

Small-angle X-ray measurements of the density fluctuations as a function of temperature and thermal history are performed in silica and float glass. Structural relaxation in the glass transition range is observed for the samples stabilized at high temperature. The amplitude of the density fluctuations in the glassy state depends on the thermal history for samples of same composition. It increases with fictive temperature for silica as well as for float glass. Our results are compared to previous results in oxide glasses or polymers and discussed in relation with the concept of fragility i.e. the temperature sensitivity of viscosity in the liquid state.

Electrokinetic properties of surface modified PETP fibres

The microporous structure of unmodified poly (ethylene terephthalate) PETP fibres was investigated by small-angle X-ray measurements in order to determine the content, size and shape of micro-voids in the fibres. Because of the compact and highly crystalline morphology of the chemically weakly reactive PETP fibres, the rate of diffusion within the fibres or adsorption on the surface is very low. Therefore a technique for modifying polyester fibre surface to change the dyeability, water sorption properties and electrokinetic characteristics have been suggested and used. It includes the adsorption of some electrolytes on the fibre surface. In order to study the obtained fibre surface changes the zeta-potential ζ was determined by streaming potential measurements as a function of pH. PETP fibres exhibit high negative ζ plateau value, due to their strong hydrophobicity and non-ionic character. The application of the surfactant changes the electrokinetic properties with respect to the adsorption process conditions.

Pore Structure in Carbon Fibers Prepared from Polymer Blend

Pore structure in carbon fibers prepared from a polymer blend has been investigated by measurements of small-angle X-ray scattering (SAXS). Generally, an application of the SAXS method to analyze the pore structure of carbon materials is not so easy, because that in carbon materials is complex and structure correlation between pores cannot be neglected. The polymer blend method does not use the activation process and makes it possible to control the size and concentration of pores dependent on the pore forming resin. It can be said that the present result is positioned as one of the most successful results among pore structure determinations by SAXS, and that the result will become a standard for the study of pore structure in carbon materials.

A SAXS study of kinetics of aggregation of TEOS-derived sonogels at different temperatures

The kinetics of aggregation of tetraethoxysilane (TEOS)-derived silica sols, produced by acid-catalyzed and ultrasound-stimulated hydrolysis, were studied by `in situ' measurements of small-angle X-ray scattering (SAXS) at the temperatures 40°C, 60°C and 70°C. The results were analyzed in terms of the evolution with time ( t) of the SAXS intensity probing the mass fractal characteristics of the system, the average radius of gyration ( R G) of the clusters and the number of primary particles per cluster. The aggregation process yields mass fractal structures which exhibit a scattering exponent ( α) practically equal to 2, in the probed length scale range (5.3 nm <1/q<0.22 nm) , beneath and even far beyond the gel point. This suggests that α is a direct measure of the real mass fractal dimension ( D) of the structure. The precursor sol (pH=2) exhibits 1 nm mean sized clusters with mass fractal dimension D∼1.9. Increasing the pH to 4.5, the cluster mean size and the number of primary particles per cluster increase but the system keeps a more opened structure ( D∼1.4). In the first aggregation stages, D increases up to ∼2 by incorporating primary particles to the clusters without changing their mean size. From this stage, the aggregation progresses following a thermally activated scaling law well described by R G∼ t 1/ D in all cases. This is indicative of a diffusion-controlled cluster–cluster aggregation process. The activation energy of the process was found to be 91.7 kJ/mol.

Nucleation and growth of AgCl clusters in a sodium borate glass: Numerical analysis and SAXS results

By solving a set of differential rate equations the precipitation of AgCl clusters in the glass system 30Na2O–70B2O3/AgCl has been modeled. Using a parallel algorithm on a CRAY T3E it was possible to investigate the process of homogeneous nucleation and growth, which starts after an initial quench of the glass melt into the miscibility gap of the phase diagram, even including the onset of the Ostwald ripening stage. The method has been applied to the examination of the intermediate stage between independent growth and Ostwald ripening. In particular, the influence of the interfacial tension and the temperature of heat treatment on the evolution of the silver halide clusters has been investigated. The results are in qualitative agreement with those of in situ measurements of small-angle x-ray scattering. Furthermore, general consequences for the interpretation of experimental data on nucleation and growth have been derived.