Small-angle X-ray Measurements Research Articles

Simultaneous measurements of small angle x-ray scattering, wide angle x-ray scattering, and dielectric spectroscopy during crystallization of polymers

A novel experimental setup is described which allows one to obtain detailed information on structural and dynamical changes in polymers during crystallization. This technique includes simultaneous measurements of small angle-wide angle x-ray scattering and dielectric spectroscopy (SWD). The capabilities of the technique have been probed by following in real time the crystallization process of a model crystallizable polymer: poly(ethylene terephthalate). By performing these experiments, simultaneous information from both, the amorphous and the crystalline phase is obtained providing a complete description of changes occurring during a crystallization process. The SWD technique opens up new promising perspectives for the experimental study of the relation between structure and dynamics in materials science.

Polyelectrolyte-induced vesicle formation in lamellar liquid-crystalline model systems

The object of the research was to investigate the influence of a semiflexible polyanion (carboxymethylcellulose) in the absence and presence of a more flexible cationic polyelectrolyte [poly(diallyldimethyl-ammonium chloride)] on structure formation in liquid-crystalline model systems consisting of sodium dodecyl sulfate (SDS)/ decanol/water. Small-angle X-ray measurements in combination with electron microscopic investigations show the adsorption of the polycation on the SDS head groups. These polymer-modified lamellae form multilamellar vesicles. The semiflexible polyanion was embedded into the liquid crystal without macroscopic phase separation and multivesicular vesicles were formed on the supramolecular level. In combination the oppositely charged polyelectrolytes induce the formation of multivesicular structures where two lamellar structures coexist.

Effect of a Nonadsorbing Polymer on the Stability of a Two-Solvent Lamellar Phase: Experimental and Theoretical Study of Critical Points of Lamellar/Lamellar Phase Separations

We investigate how the elastic properties of a two-solvent lyotropic lamellar phase are modified by the addition of a nonadsorbing water-soluble homopolymer (polyvynilpyrolidone). The initial two-solvent lyotropic lamellar phase consists of a regular stack of surfactant monolayers made from a mixture of nonionic surfactants (TX100/TX35) and a cationic surfactant (cetylpyridinium chloride) which separate successive layers of oil (decane) or water. By modifying the relative proportions of the various components of the lamellar phase or the temperature, we are able to control the magnitudes of the different contributions to physical interactions between the bilayers. From small-angle X-ray measurements on this system, we have identified four different critical Lα/Lα phase separations. At such critical points the corresponding smectic susceptibility B-1 diverges. In an attempt to better understand these experimental results we present a general calculation of the smectic compression modulus B of a four-comp...

Molecular dimensions in the δ and γ phases of syndiotactic polystyrene, using small angle neutron scattering

The δ phase of syndiotactic polystyrene/ethylbenzene has previously been shown to involve a sheet-like arrangement of crystal stems, with superfolding at higher molecular weights. SANS measurements have been made using tilted samples in order to separate in-plane and out-of-plane radii of gyration. Use of intensities from the whole area of the detector allows the determination of these quantities with good precision. Comparison between the out-of-plane radius and the long spacing determined from small angle X-ray measurements shows close agreement for the lower molecular weight ( M ̄ w =42 700) in both δ and γ phases, while R z is a factor of 2 larger for the higher molecular weight ( M ̄ w =124 500). This indicates that each molecule occupies a single lamella at the lower molecular weight and, on average, two lamellae at the higher one, in both δ and γ phases. This provides clear evidence of tie molecules at the higher molecular weight, and also implies that the δ to γ phase transition only involves a reorganisation of chain segments within those lamellae which originally contained the molecule.

Structure and properties of bis(2-ethyhexyl)phospheric acid microemulsions with a network structure: Effect of counter-ions

Several physicochemical properties were experimentally examined for calcium bis(2-ethylhexyl)phosphate (Ca(DEHP) 2)/water/ n-hexane/calcium chloride systems and compared with sodium bis(2-ethylhexyl)phosphate (NaDEHP)/water/ n-hexane/sodium chloride systems in the Winsor II regime to elucidate the effect of changing counter-ion species on the properties of a microemulsion in the amphiphile-concentrated region characterized by the presence of a network-like structure formed from worm-like molecular assemblies. The measurements of small angle X-ray scattering, shear viscosity, electroconductivity were consistently interpreted in terms of the strong tendency of molecular assemblies to become more elongated for Ca 2+ than for Na +. The dependence of the dynamical correlation length on the volume fraction of molecular assembly obtained from the dynamic light scattering implies that the freely mobile part in the Ca(DEHP) 2 micoemulsion network would be determined by the individual micromechanical property of the worm-like molecular assembly, being different from that in NaDEHP systems determined by the network mesh which becomes more confined with the increase in the volume fraction of the molecular assembly.

Preparation and size evaluation of nanometer gadolinium powder

Nanometer-size gadolinium powders (nm-Gd) have been prepared by means of evaporation condensation of Gd atoms within inert gas atmosphere. Microscopic analyses, based on measurements of small angle x-ray scattering (SAXS), x-ray diffraction (XRD), Raman scattering spectrum (RSS), and observation with transmission electron microscope (TEM), have been carried out in order to evaluate the size and size distribution of the as-prepared nm-Gd powder. It turns out that the size distribution function of nm-Gd powder agrees very well with the distribution function of Rayleigh instead of logarithmic distribution. The mean size d of nm-Gd powders bears a linear relationship with the logarithm of the pressure p of the inert gas atmosphere as follows: d = a + b · ln p. A discussion concerning the influence of particle size of nm-Gd powder on nanostructured material parameters such as the size distribution, specific surface area, and the percentage of interface atoms have been given in detail.

Research on radiation stability of polypropylene

The effect of isotacticity of polypropylene(PP) on its radiation stability has been investigated in the present work. It was found that (1) The G value of H 2 and CH 4 is smaller if isotacticity of PP is higher; (2) It is easier to be crosslinked by radiation for the PP with higher isotacticity; (3) The shape of DSC peak changes smaller after irradiation for PP with higher isotacticity. These results have been explained by the measurement of 13C-NMR and small angle X-ray scattering.

A core-shell model of calcium phosphate nanoclusters stabilized by beta-casein phosphopeptides, derived from sedimentation equilibrium and small-angle X-ray and neutron-scattering measurements.

Calcium phosphate nanoclusters were prepared under standardised conditions using 10 mg ml(-1) of the 25-amino-acid N-terminal tryptic phosphopeptide of bovine beta-casein as a stabilising agent. The Mr determined by sedimentation equilibrium was 197,600+/-13,700 and the apparent radius of gyration determined by X-ray scattering was 2.80+/-0.05 nm. A small-angle neutron scattering contrast variation study in 1H2O/2H2O mixtures was performed and gave radii of gyration at the calculated match points for the calcium phosphate (88.2% 2H2O) and phosphopeptide (41.3% 2H2O) of 3.39+/-0.08 nm and 1.85+/-0.05 nm, respectively. Measurements at larger scattering wave vector showed a subsidiary maximum at about Q = 1.6 nm(-1). The results are consistent with a model of the nanoclusters comprising a spherical core of 355+/-20 CaHPO4 x 2 H2O units, density 2.31 g ml(-1) and radius 2.30+/-0.05 nm surrounded by 49+/-4 peptide chains with a partial specific volume of 0.7 cm3 g(-1), forming a tightly packed shell with an outer radius of 4.04+/-0.15 nm. This model suggests that the phosphopeptide is able to arrest the process of growth of the precipitating phase of calcium phosphate at its earliest stages. A similar role for whole casein could be vital to the normal functioning of the mammary gland during milk secretion.

Phase Behavior and Structure of Ternary Amphiphilic Block Copolymer−Alkanol−Water Systems: Comparison of Poly(ethylene oxide)/Poly(propylene oxide) to Poly(ethylene oxide)/Poly(tetrahydrofuran) Copolymers

The phase behavior of amphiphilic copolymer−alkanol−water ternary systems was investigated for triblock copolymers of similar molecular weight and the same hydrophilic block [poly(ethylene oxide), E] but having different hydrophobic blocks [poly(propylene oxide), P, or poly(n-butylene oxide) = poly(tetrahydrofuran), T]. The alkanol used (butan-1-ol) was comparable in terms of chemical composition to the hydrophobic segments. A rich phase behavior was obtained for the polymer with the P middle block (Pluronic F127, E100P70E100): five different one-phase regions, i.e., micellar (L1) and reverse micellar (L2) solutions, and (micellar) cubic (I1), hexagonal (H1), and lamellar (Lα) lyotropic liquid crystalline regions, were detected. The microstructure in the liquid crystalline regions was established from small-angle X-ray measurements; I1 was found to be primitive cubic. The alkanol molecules are most likely anchored with their OH− group at the E−P interface, increasing the apparent volume of the P blocks relative to that of the E blocks, and thus causing a decrease in the polymer layer curvature from spherical to cylindrical. Only a single one-phase region, extending from the water to the alkanol corner, was observed in the E100T27E100 ternary phase diagram. The extent of the one-phase regions decreased for both E100T27E100 and E100P70E100 systems when the alkanol molecular weight increased.

Determination of the transition region thickness in polymer blends by the SAXS method

The width of domain boundaries is an important parameter for the characterization of microphase separation in polymers. This parameter is often obtained by measurements of small-angle X-ray scattering (SAXS) in the range of validity of Porod's law, according to which X-ray intensity scattered by an ideal two-phase system decreases with the scattering vector h as h-4. Here h is defined as h = (4π sin)/λ, where is half the scattering angle and λ the wave-length of the X-ray. If the interface boundary is diffuse, i.e. the electron density does not change stepwise between separated phases but changes continuously in certain transition regions with a finite thickness, the intensity of scattering decreases more rapidly than predicted by Porod's law. In the present paper we have used the SAXS method in order to determine the supermolecular structure parameters, including the transition layer thickness, of polypropylene/polyamide-6 (PP/PA) blends. The transition layer thickness has been obtained by two methods elaborated by Koberstein and co-workers [4] and by Ruland [1], respectively. Both these methods assume that changes of the electron density in the transition region can be described by a Gaussian function with a standard deviation σ. The parameter σ have been determined graphically from the appropriate plots. Then, the thickness of the phase boundary, E, was estimated as √12σ. The investigated PP/ PA blends are multiphase systems and the problem of determination of the boundary width is more complicated because the meaning of Porod's law must be considered with caution. This problem is discussed based on a wide range of investigated samples prepared over various pressure and crystallization temperature conditions.

Measurement of the Gaussian curvature of the surfactant film in an isometric bicontinuous one-phase microemulsion.

Small-angle x-ray and neutron-scattering (SAXS and SANS) measurements are made of a three-component isometric microemulsion, ${\mathrm{C}}_{10}$${\mathrm{E}}_{4}$-${\mathrm{D}}_{2}$O-octane, in the one-phase channel around the hydrophile-lipophile balance temperature of the system. A previous SANS contrast variation experiment indicated that the microstructure of this isometric microemulsion is bicontinuous in water and oil, with the surfactant film having a zero mean curvature. We analyze the SAXS and SANS data taken with a bulk contrast in terms of a modified Berk's random wave model. We choose a spectral function which is an inverse sixth-order polynomial, with three parameters $a$, $b$, and $c$, as introduced by Lee and Chen earlier. This three-parameter spectral function is then used in conjunction with Cahn's clipping scheme to obtain the Debye correlation function for the microemulsion. The analysis gives an excellent agreement with the intensity data in an absolute scale. We then use the three parameters so obtained to calculate the mean Gaussian curvature of the surfactant film. We also show a three-dimensional-reconstructed morphology of the microemulsion.

Solid-state NMR analysis of blends of nylon 6 and zinc salts of sulfonated polystyrene ionomers

Solid-state NMR was used to establish the specific intermolecular interactions responsible for the miscibility of blends of nylon 6 (PA6) and the zinc salt of lightly sulfonated polystyrene (Zn-SPS) and to characterize the scale of molecular mixing. l3C CPIMAS spectroscopy identified the interpolymer interaction as a complex between the Zn2+ cation of the ionomer and the amide nitrogen. Measurements of the lH spin-lattice relaxation times, TIH and TIPH, indicated that mixing of the two polymers in the amorphous phase occurred at least down to a size scale of 2 nm. TIPH measurements also revealed a microphase of >2.5-3.5 nm in the neat ionomer, which is consistent with the size of ionic domains inferred from previous small-angle X-ray (SAXS) measurements. Adding PA6 to Zn-SPS reduced the microheterogeneity in the ionomer as measured by TI,.

Thermal diffusivity measurement of LiNbO 3 melts doped with MgO by the laser flash method

Thermal diffusivities of LiNbO 3 melts doped with 0, 2 and 5 mol% MgO at 1523–1604 K have been determined by the laser flash method. The experimental values are in the range of (2.7×3.2) x10 -7 m 2⧸ s with weak positive temperature dependence for each composition. The variation of thermal diffusivity by adding MgO up to 5 mol% is negligibly small, in contrast to the results of density, surface tension and shear viscosity. No anomalous behavior of thermal diffusivity was also observed at temperature near the melting point where a certain change in melt structure has been suggested by the measurements of shear viscosity and small angle X-ray scattering.

A multilayer analyser suitable for linear detection of anomalous small-angle X-ray scattering

Measurements of anomalous small-angle X-ray scattering often include a strong fluorescent background. The separation of the elastic scattering from the background is usually performed at the time of analysis. This paper presents an alternative experimental method using a multilayer analyser compatible with a linear position-sensitive detector and, for a test case, compares the resulting structure factors with those obtained by the usual technique. The technique achieves the proposed goal but at the expense of counting rate.

Equilibrium and nonequilibrium contributions to x-ray scattering from supercooled water.

Percolation theory for supercooled water predicts an enhanced intensity in the low-q range of the spectrum. In small-angle x-ray measurements on water in the \ensuremath{\Vert}q\ensuremath{\Vert} range 0.4--1.8 ${\mathrm{nm}}^{\mathrm{\ensuremath{-}}1}$ and the temperature range 273--253 K, no enhanced intensity could be measured. The spectra just follow the normal equilibrium thermodynamic behavior. A nonequilibrium enhanced intensity is observed in the spectra of supercooled water in vertically mounted capillaries in the \ensuremath{\Vert}q\ensuremath{\Vert} range below 0.3 ${\mathrm{nm}}^{\mathrm{\ensuremath{-}}1}$. This intensity is due to convection in the capillaries.

Annealing effects in ferroelectric poly(vinylidene fluoride-trifluoroethylene) copolymers: real-time studies using synchrotron radiation

Poly(vinylidene fluoride-trifluoroethylene) (P(VF 2-TrFE)) copolymers with about 30 mol% of TrFE exhibit a ferroelectric transition of first-order type around 100°C. This transition is investigated using complementary measurements of small angle X-ray scattering and wide angle X-ray diffraction. The results provide information on the properties of both the amorphous and crystalline phases as a function of temperature and on the lamellar morphology. They show that temperature cycling through the Curie transition increases the degree of crystallinity of the polymer and modifies the structure.

Small‐angle x‐ray scattering studies of fibrin film: Comparisons of fine and coarse films prepared with thrombin and ancrod

Measurements of small-angle x-ray scattering have been made on films prepared from fine and coarse (i.e., formed at high and low, respectively, pH and ionic strength) clots of bovine fibrin by osmotic shrinkage or compression in one dimension. Intensity profiles were obtained with pinhole geometry on films stretched up to a stretch ratio of 1.43. In unstretched coarse films, repeat spacings were seen at about 245, 120, and 77-80 A. These peaks can probably be identified with the first, second, and third orders of the well-known fibrin repeat of 225 A. In unstretched fine films, only the 77-80 A spacing was seen. In this case, the first two orders may be weak because the half-staggered arrangement of monomer units giving rise to the 225 A reflection is not reinforced by lateral aggregation of protofibrils; the third order may be strong since the molecular subdomains appear to divide the repeat roughly into thirds. After stretching, the 77-80 A spacing persisted in the meridional direction but almost disappeared in the equatorial. Experiments on unstretched films prepared with ancrod substituted for thrombin gave similar results.

Temperature-jump apparatus and measuring system for synchrotron solution x-ray scattering experiments

A rapid temperature-jump (T-J) device was designed for the kinetic measurements of small-angle x-ray scattering from solutions of biological macromolecular systems. The dead time of the apparatus is reduced to a few hundred milliseconds. The structural change of biological macromolecules in solutions can be monitored in the time scale of a few hundred milliseconds by the synchrotron small-angle x-ray scattering with a combination of a CAMAC data-acquisition system and the present T-J apparatus.

Emulsifying Characteristics of α-Monoalkyl Glyceryl Ether

α-Monoisostearyl glyceryl ether (GE) is a surfactant with less solubility into water, and forms the lyotropic liquid crystal with a reversed hexagonal structure even at lower concentrations. GE was found to be such a characteristic emulisifier that it gave stable water-in-oil (W/O) emulsions against a coalescence of water droplets, even though the water content of the emulsion was extremely high. The emulsion became more stable as increased in the water concentration.The structure of the emulsions was investigated through the study of the ternary phase diagrams and the measurement of small angle X-ray scattering, indicating that the liquid crystalline phase composed of GE, water and oil was formed in the emulsion. The electron microscopic observation showed that the interfacial layer between oil and water phases in the emulsion was the liquid crystal. And in case of higher water concentrations, the continuous phase itself was composed of the liquid crystal. These interfacial layers are considered to be mechanically so tough that the W/O emulsions were stable against a coalescence of water droplets.Thus it was concluded that the W/O emulsions stabilized with GE was, in fact, water-in-liquid crystal (W/LC) emulsion.

A1-4 mass%Zn合金の2段時効と球状GPゾーンの析出

Effect of pre-aging at 243 K or 273K on subsequent aging at 263 K (two-step aging) in Al-4 mass%Zn alloy was studied by measurements of electrical resistance and small-angle X-ray scattering (SAXS) intensity.When pre-aging time (tApre) was relatively short (<600 s), the final value of the electrical resistivity (ρE) on the aging at 263 K was not affected by the pre-aging. As tApre became longer (>600 s), complicated behavior of ρE was observed according to the change of tApre at 243 K or 273 K.In the case of pre-aging at 273 K the SAXS integrated intensity (q0) of thick specimens after the aging at 263 K decreased gradually from the value of not pre-aged specimens (q0263) with increasing tApre. On the thick specimen pre-aged at 243 K, except when tApre was very long, q0 was, within experimental error, not affected by the pre-aging, regardless of the complicated change of ρE.Concerning thin specimen pre-aged at 243 K, in which annihilation of the vacancies at the surfaces could not be neglected, q0 after aging for long time at 263 K increased to q0263 of the thick specimens, exceeding q0 of the specimen aged at 263 K without pre-aging, as tApre was increased. For very long tApre q0 only reverted partially to a value larger than q0263.The SAXS results have been discussed in terms of reduction in concentration of quenched-in vacancies during the pre-aging and of volume fraction of GP zone.In spite that q0 that was attained on the pre-aging for not so long time at 243 K was fairly smaller than q0263, q0 reduced at the initial stages of subsequent aging at 263 K. It was considered that this reduction would suggest the dissolution of the small GP zones formed at 243 K, even though the solid solution was supersaturated.