Small-angle X-ray scattering from heparin in solution

Summary X-ray small-angle scattering fron heparin in solution was measured, and compared with theoretical curves based on various nolecular models. Good agreement was obtained for the model consisting of -D-glcosamine in the ⁴C₁ conformation and -L-iduronate in the ¹C₄ conformation. It was suggested that the helical conformation is maintained even in solution, at least in part. The helix pitch was estimated to be 0.75–0.85 nm.     

Small-angle X-ray scattering in type Ia diamonds

The results of a small-angle X-ray scattering (SAXS) investigation of natural and synthetic diamonds, with different types of nitrogen-related defects, are presented. They reveal a presence of impurity-rich spherical clusters with a diameter of approximately 90 Å in an IaB diamond. SAXS scattering in an IaA diamond has a much lower intensity, and originates from larger clusters with a considerable variation in size. It is likely that the dominant impurity in these clusters is nitrogen. Present data suggest the possibility that some of the nitrogen-related point defects (A- and B-centers) are not randomly distributed in the diamond lattice, but instead are concentrated in clusters. It is suggested that, although optical manifestations of the A-nitrogen are similar in different diamonds, IaA diamonds can be divided into two sub-groups. The IaA₁ group includes annealed, synthetic, and some natural diamonds. They contain randomly distributed nitrogen pairs, which do not influence mechanical properties and do not produce X-ray scattering. In the IaA₂ group, the diamond aggregation process went further and the formation of nitrogen-containing clusters began. The process of nitrogen aggregation is described in terms of the decay of a supersaturated solid solution of nitrogen in diamond. The driving force for the creation of impurity clusters is the lowering of the free energy of nitrogen dissolution in the diamond lattice, and the decrease of strain.     

Small-angle X-ray scattering study of halato-telechelic polybutadienes

Summary The small-angle X-ray scattering curves of carboxy-telechelic polymers exhibit very strong scattering at the lowest angles which points to the presence of large aggregates in the samples. Beyond the position of the main scattering maximum, common to all ionomers, a faint modulation is observed at a position corresponding to a second diffraction order. These observations are discussed with respect to other data in the litterature.     

Small-angle X-ray scattering of long-period structures forming bundles

Small-angle X-ray scattering (SAXS) patterns have been calculated based on a structure model, which consisted of the bundles of long-period structures. The proposed model has produced various scattering patterns of polymers, such as the equatorial, layer line, four-spot, droplet-shaped and triangular scattering. The 0.5th order scattering has arisen when the disorder in or between the long-period structures was large even though the structure did not have the periodicity directly related to the scattering maximum. A slight decrease in the disorder due to slip between the long-period structures has accounted for the sudden change of the SAXS pattern of a poly(ethylene terephthalate) fiber from the four-spot to the layer line scattering which was caused by a slight tensile deformation.     

Small-angle neutron scattering studies on sodium dodecylbenzenesulfonate-tetra-n-butylammonium bromide systems

A phase study was completed on aqueous sodium dodecylbenzenesulfonate (SDBS) and tetra-n-butyl-ammonium bromide (Bu₄NBr) systems, and consolute boundaries were drawn through cloud points. Samples were selected from both miscibility regions [under the lower consolute boundary (LCB) and above the upper consolute boundary (UCB)] for small-angle neutron scattering (SANS) studies. In the first set of experiments, the effect of varying Bu₄NBr concentration on micellular parameters of 100 mM SDBS was studied at 30°C. The pure SDBS micelle has an aggregation number (n _s ) of 51, and the effective charge on the monomer (α) is 0.17. With the addition of Bu₄NBr, the n _s of SDBS micelles increases while α decreases. The system with [Bu₄NBr]=39.5 mM (an above-UCB sample) showed clouding near room temperature (≈29°C) and had a high n _s value (300) and a low α (=0.09). The data indicated that the micelles lose ionic character in the presence of Bu₄NBr. The temperature effect on this sample shows that α remains almost constant, while n _s decreases on heating. A similar effect was observed with samples of lower Bu₄NBr concentration (32 or 25 mM) in the presence of 100 mM SDBS. The same type of temperature effect was seen on a sample of under-LCB region (50 mM SDBS+32 mM Bu₄NBr); the n _s values increased significantly as the LCB was approached. The overall SANS observations suggest that the micelles have low ionic character together with high n _s values (a case of micellar growth) near LCB/UCB.     

Small-angle neutron scattering study on block and gradient copolymer aqueous solutions

The small-angle neutron scattering investigation was carried out on semi-dilute aqueous solutions of block and gradient copolymers comprising pEOVE and pMOVE, pEOVE₃₀₀-block-pMOVE₃₀₀ (Block) and p(EOVE-grad-MOVE)₆₀₀ (Grad). Here, pEOVE and pMOVE denote poly(2-ethoxyethyl vinyl ether) and poly(2-methoxyethyl vinyl ether), respectively, and the numbers indicate the degrees of polymerization. The monomer composition in the Grad had a gradient along the polymer chain. For 20.0 wt% solutions, a microphase-separated structure and physical gelation were observed both in Block and in Grad systems. In the case of the Grad system, a gradual microphase separation took place as a function of temperature via a micellization with a small radius of core, characterized by the “reel-in” process, i.e., a winding of polymer chains to the core of a micelle because of the gradient composition. On the other hand, the Block system underwent a stepwise transition with respect to temperature. The relationship between microphase separation and the rheological behavior is explained from the viewpoint of microscopic structure.     

Small-angle X-ray scattering studies of a natural fiber: Agave cantala

Summary Agave cantala, a natural fiber is considered as a densely packed colloidal system belonging to the general micelle system and the well known theories of KRATKY and POROD have been utilized to evaluate some macromolecular parameters of the scattering inhomogeneities in it. The small-angle KRATKY Camera of the latest design has been used for experimental measurements. The parameters evaluated are the specific inner surface, transversal lengths like the length of inhomogeneity and the length of coherence and the air fraction of the scattering particles in Agave cantala fiber; these were found to be     

Small-angle neutron scattering from branched epoxide resins

Small-angle neutron scattering experiments in the range of q² from 0.01 to 25 nm⁻² have been carried out on branched epoxide resins based on bisphenol-A at the Institute Laue—Langevin (I.L.L) in Grenoble (q=(4π/λ) sin(θ/2)). Measurements were made with six samples in the range of M_W from 1500 to 19 000 and four concentrations between 1.3 and 10% (w/w) in deuterated diglyme. The results are as follows: (i) The mean square radius of gyration follows a relationship S²_z=4.69×10⁻⁴M^1.20_W (nm²). (ii) In all cases fairly large second virial coefficients A₂ are obtained which, however, decrease strongly with molecular weight. Above M_W=2500, the virial coefficient follows the relationship A₂=1.6M^−0.85_W (mol cm³g⁻²). (ii) The reciprocal particle scattering factor as a function of q² exhibits only a slight upturn and otherwise shows the behaviour of a randomly branched polycondensate. The slight upturn is discussed as being caused by the finite volume of the monomeric unit. Possible reasons for the high exponent in the S²_z versus M_W dependence are briefly discussed.     

Small-angle X-ray scattering experiments and computer simulations to characterise anisotropy of activated carbons prepared from wood

Small-angle scattering was measured from activated carbon monoliths prepared from three different wood species (European beech, Pedunculate oak and Norwegian spruce). Substantial differences were found in the scattering images of axial and tangential slices, attributed to their characteristic phytogenic structures. The decrease in anisotropy in the nanostructured carbon matrix due to the activation process is also different among the three investigated types of wood. For quantitative characterization of the anisotropy and its decrease, the degree of alignment was calculated from the azimuthal scattering curves. A simple numeric model was constructed on the basis of direct information obtained by atomic force microscopy. Scattering patterns calculated from the model were compared with the experimental ones to explain the possible structural changes in the carbon skeleton.     

Small-angle neutron scattering from a polymer coil undergoing stress relaxation

Small-angle neutron scattering measurements have been made on samples of polystyrene in which the stress has been allowed to relax at a constant strain. The radii of gyration parallel and perpendicular to the stretch direction have been measured as a function of time after the strain has been applied. After an initial rapid change, the radii of gyration tend towards asymptotic values which are close to those for the undeformed chain. The deformation appears to behave as if the affine deformation theory holds only for distances separating effective crosslinks. It is proposed that after the initial change in radii of gyration the stress is relieved by reorientation of the chain segments.     

Thermodynamic modeling of gas solubility in aqueous sodium chloride solution

An electrolyte Equation of State is presented by combining the Cubic Plus Association Equation of State,Mean Spherical Approximation and the Born equation.This new model uses experimental relative static permittivity,intend to predict well the activity coefficients of individual ions (ACI) and liquid densities of aqueous solutions.This new model is applied to model water + NaCl binary system and water + gas +NaCl ternary systems.The cation/anion-water interaction parameters of are obtained by fitting the exper-imental data of ACI,mean ionic activity coefficients (MIAC) and liquid densities of water + NaCl binary system.The cation/anion-gas interaction parameters are obtained by fitting the experimental data of gas solubilities in aqueous NaCl solutions.The modeling results show that this new model can correlate well with the phase equilibrium and volumetric properties.Without gas,predictions for ACI,MIAC,and liquid densities present relative average deviations of 1.3％,3.6％ and 1.4％ compared to experimental ref-erence values.For most gas-containing systems,predictions for gas solubilities present relative average deviations lower than 7.0％.Further,the contributions of ACI,and salting effects of NaCl on gases are ana-lyzed and discussed.     

Small-angle neutron scattering by semicrystalline polyethylene

The angular dependence of the intensity of neutron scattering by deuterated polyethylene chains (PED) dispersed in the protonated host (PEH) in the semicrystalline state has been computed over the scattering range $\text{0 < μ < 0.2}\text{A}\text{?}{}^{\mathrm{?1}}$, where μ = (4π/λ)sin(θ/2), for various morphologies that differ according to the mode of chain re-entry into the crystalline lamellae. The scattering functions vary strongly with the tendency for adjacent re-entry. The intensity in the range $\text{0.04 < μ < 0.10}\text{A}\text{?}{}^{\mathrm{?1}}$ is 30–40% greater for the regularly folded morphology than for the ‘switchboard’ model. Calculations for the latter approximate the experimental results of Schelten et al. Optimum agreement with their scattering intensities, and the chain dimensions and degree of crystallinity as well, is achieved by a statistical model in which the chain preferentially re-enters the crystalline layer with a probability of about 0.7. Re-entry, when it occurs, is not required to be adjacent to the preceding sequence.     

钠钙氯化物在乳糖水中热力学性质的确定

在298.15 K时利用电动势法确定四元体系氯化钠-氯化钙-乳糖-水不同组成(乳糖质量分数分别为0,5%,10%和15%)时的热力学性质。利用Pitzer离子作用模型拟合实验数据,获得了氯化钠和氯化钙在乳糖水混合溶剂中的Pitzer模型参数。进一步计算了氯化钠和氯化钙从纯水到乳糖水混合溶剂中的迁移吉布斯函数。获得了氯化钠和氯化钙混合电解质在乳糖水混合溶剂中的混合参数θ(Na Ca)和ψ(Na Ca Cl)。计算了298.15 K时四元体系中氯化钠和氯化钙的平均离子活度系数。结果发现:利用Pitzer高阶静电作用模型计算混合电解质在混合溶剂中的平均离子活度系数,能获得较为满意的结果。     

Concentration of sodium chloride in aqueous solution by chlorodifluoromethane gas hydrate

The decomposition temperature and pressure (quadruple point) of chlorodifluoromethane (R22) gas hydrate in aqueous sodium chloride (NaCl) solution was measured at different NaCl concentrations in the solution as a phase diagram. The operative concentration curve of NaCl was obtained as a function of temperature. The maximum decomposition temperature of R22 hydrate was about 290 K at 0.9 MPa pressure, and it decreased as the NaCl concentration increased in the solution. R22 hydrate caused supercooling, and the supercooling occurrence temperature was much lower than the decomposition temperature. The ultrasonic charge reduced the supercooling of hydration effectively even though the ultrasonic charge did not change the decomposition temperature at all. The concentration experimental results from the several NaCl solutions having different NaCl concentrations were in good agreement with the theoretical operative concentration curve for NaCl.