Small-angle X-ray Scattering Peak Research Articles

The evidences for the existence of evanescent wave-induced scattering in the transmission SAXS of high-density polyethylene

In an earlier study of ours (Li et al., IUCrJ,2019 6, 968–983), we conjectured that small-angle X-ray scattering (SAXS) in semicrystalline polymers might be from evanescence wave-induced scattering (Ievi) rather than claimed by classical scattering theory, the incident X-ray-induced scattering (Iin). In this study, we systematically compared Ievi and Iin under the influence of various factors, i.e., linear crystallinity, the number of lamellar crystals (N), the characteristic penetration depth of evanescent wave (dp*) and long period distribution, identifying the method to distinguish SAXS in semicrystalline polymers is from Iin or Ievi. Applying this method to SAXS of a high-density polyethylene (HDPE) sample, it was found that even excluding the influence of instrumental broadening and lamellar thickness/long period dispersity, the SAXS peak in HDPE is still greater than theoretically maximum peak width induced by Iin, indicating the SAXS in HDPE is not induced by incident X-ray directly. Excluding the interference of long period dispersity, it was found that dp* was around 5.9 nm, clearly demonstrating the existence of evanescent wave. Besides, results indicated that the lateral size determined with new theory is accurate, which in turn demonstrated that our assumption that Ievi is from a lamellar stack parallel to incident X-ray is reasonable. Taking all evidences together, it can be concluded safely that SAXS in HDPE is induced by evanescent wave.

Structural study on Ti-ion complexes in concentrated aqueous electrolytes: Raman spectroscopy and high-energy X-ray total scattering

Abstract We report a structural study on the characterization of specific structures of Ti-ion complexes in the ion-concentrated aqueous sulfuric acid solutions, which are promising new-type redox flow battery electrolytes. On the basis of the quantitative analysis of Raman spectra, we successfully determined the coordination number of SO4 ions (nSO4) within the Ti-ion complexes in solutions. The resulting nSO4 values depended on the Ti ion and SO4 concentrations (cTi and cSO4, respectively), which implied the formation of multinuclear Ti-ion complexes in the highly concentrated solutions. High-energy X-ray total scattering (HEXTS) measurements indicated that Ti4+ ions formed nanoscale aggregates that are based on the multinuclear complexes, e.g., chain-like -Ti-O-Ti-O– structures; indeed, characteristic small-angle X-ray scattering (SAXS) was observed for high cSO4 solutions. We determined that the SAXS peak decreased in intensity when Ti4+ electrochemically reduced to Ti3+ in solutions, and the extent of decrease was considerably more at higher Ti3+ concentrations. The local structures of such Ti-ion complexes were evaluated on the basis of the radial distribution function G(r), and we discuss the charge effect of Ti ions on the complex structures at the molecular level. We concluded that the reductive reaction of Ti4+ to Ti3+ triggers a change in the solution structure, i.e., nanoscale Ti4+ aggregates were disrupted and yielded mononuclear Ti3+ complexes.

Influence of Macrodiol on Phase Separation and Crystallization Processes in Hard-Phase Reinforced Polyurethane Elastomers Based on Isocyanates of Variable Conformational Mobility

An investigation was performed to determine how aspects of microstructural changes in polyurethane elastomers vary with composition: the hard segment and soft segment were varied in a family of six segmented copolyurethane elastomers. Two hard segments were compared, based on the rigid model diisocyanate 4,4′-methylene bis(phenyl isocyanate) (MDI) or a novel flexible 4,4′-dibenzyl diisocyanate (DBDI). The hard segment fraction was held constant at approximately 40%. The soft segment macrodiols were polyesteric poly(butylene adipate) (PBA) and poly(caprolactone) glycol (PCD), or polyetheric polytetrahydrofuran (PTHF). The molar masses were 2000 ± 50 g mol−1 for PBA and PTHF and 1250 ± 50 g mol−1 for PCD. For all materials, the chain extender used in the synthesis was butylene glycol (BG). Materials were studied using wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS). There was no indication of crystallinity arising from the soft segments in these materials. The broad WAXS peaks measured for the elastomers found no crystalline domains for the hard segments with MDI, while for the materials achieved with DBDI, high crystallinity is observed. All materials with PTHF showed much higher intensity in SAXS. Due to less hydrogen bonding, irrespective of the type of diisocyanate, all the materials with PTHF displayed higher phase segregation (quantified in terms of the SAXS peak areas).

Supramolecular Soft Adhesive Materials

AbstractThe rheological and adhesive properties of bis‐urea functionalized low‐molecular‐weight polyisobutylenes (PIBUT) are investigated. The polymers, which can interact through supramolecular hydrogen bonds, can self‐organize over times of the order of days at room temperature. This organized structure has been identified by small angle X‐ray scattering (SAXS) and its rheological properties indicate the behaviour of a soft viscoelastic gel. The ordered structure can be disrupted by temperature and shear so that at 80 °C, the material behaves as a highly viscoelastic fluid and no SAXS peak is observed. When cooled back at room temperature, the PIBUT retrieves its ordered structure and gel properties after 20 h of annealing. This very slow molecular dynamics gives PIBUT a highly dissipative nature upon deformation, which combined with strongly interacting moieties results in very interesting adhesive properties both on steel surfaces but more importantly on typical low adhesion surfaces such as silicone. A strategy based on the controlled incorporation of supramolecular bonds in a covalently crosslinked network appears promising for the development of a new generation of highly interacting and dissipative soft adhesives.

Small-Angle X-ray Scattering Study on Poly(ethyl acrylate-co-itaconate) Ionomers Neutralized with Various Cations

The morphology of poly(ethyl acrylate-co-itaconate) ionomers neutralized partly and fully with Na(I), Li(I) and Zn(II) was studied using a small-angle X-ray scattering (SAXS) technique. It was found that the SAXS peak position for the ionomers shifted to lower angle with increasing degree of neutralization for the ionomers containing 5.8 mol% of ionic repeat units. In the case of 11.9 mol% ionomers, with increasing degree of neutralization from 50% to 100% the SAXS peak shifted to slightly higher angles. With the density data and the space-filling concept for a simple cubic lattice, the average radii of multiplets of the ionomers were calculated. For 5.8 mol% ionomers, the radius of the Li-ionomer increased from 0.35 nm to 0.43 nm with increasing neutralization degree from 50% to 100%, and that of the Na-ionomer changed from 0.34 to 0.53 nm. In the case of the 11.9 mol% ionomers, the radius changed from 0.51 to 0.49 nm for the Li-ionomer and from 0.42 nm to 0.47 nm for the Na-ionomer. For the Zn-ionomers, only 100% neutralized ionomers showed a SAXS peak. From the SAXS profiles, the persistence lengths of the polymer chains attached to the scattering centers were also obtained.

Nanostructure Changes with Krafft Transitions of Polyelectrolyte−Surfactant Complexes in Aqueous NaCl Solutions

Nanostructure changes with the Krafft transition of complexes of poly(acrylicacid) with octadecyltrimethylammonium (PAA-OTA) in the aqueous solutions at various NaCl concentrations (Cs) from 20 to 400 mM, were studied making temperature-scanning small-angle X-ray scattering (SAXS) experiments and differential scanning calorimetric (DSC) measurements. For the PAA-OTA complex in the solution at a higher temperature than 25 degrees C, four SAXS peaks with a spacing ratio of 1:31/2:41/2:71/2, indicating the 2D hexagonal structure, were observed at Cs below 100 mM and two SAXS peaks with a spacing ratio of 1:2, indicating the lamella structure, were observed at Cs above 200 mM. For the complex in the solution at a lower temperature than 22 degrees C, a broad SAXS peak was observed at the scattering vector q = 1.2 nm-1 when the Cs was less than 200 mM but not when Cs was 400 mM. Two peaks with a spacing ratio 1:2, indicating the lamella structure, were also observed for the complex in the solution at 8 degrees C. The DSC data demonstrated that the nanostructure changes were accompanied with the endothermic enthalpy change. On the basis of the experimental results, the salt concentration dependent nanostructures are discussed.

Structural Transformations during Gelatinization of Starches in Limited Water: Combined Wide- and Small-Angle X-ray Scattering Study

Rice flour (18-25% moisture) and potato starch (20% moisture) were heated with continuous recording of the X-ray scattering during gelatinization. Rice flours displayed A-type crystallinity, which gradually decreased during gelatinization. The development of the characteristic 9 nm small-angle X-ray scattering (SAXS) peak during heating at sub-gelatinization temperatures indicated the gradual evolution into a stacked lamellar system. At higher temperatures, the crystalline and lamellar order was progressively lost. For potato starch (B-type crystallinity), no 9 nm SAXS peak was observed at ambient temperatures. Following the development of lamellar structures at sub-gelatinization temperatures, B-type crystallinity and lamellar order was lost during gelatinization. On cooling of partially gelatinized potato starch, A-type crystallinity steadily increased, but no formation of stacked lamellar structures was observed. Results were interpreted in terms of a high-temperature B- to A-type recrystallization, in which the lateral movement of double helices was accompanied by a shift along their helical axis. The latter is responsible for the inherent frustration of the lamellar stacks.

Clay Delamination in Clay/Poly(Dicyclopentadiene) Nanocomposites Quantified by Small Angle Neutron Scattering and High-Resolution Transmission Electron Microscopy

Highly delaminated clay/poly(dicyclopentadiene) nanocomposites were prepared by in-situ, ring-opening metathesis polymerization of presonicated mixtures of the liquid dicyclopentadiene (DCPD) and organically modified Montmorillonite clays. Three nanocomposite series (using Montmorillonites: I-28, I-44pa) of increasing clay loadings (0.5, 1.0, and 2.0 wt%) and modified Montmorillonite PGW (0.5 wt%) were synthesized. The dispersed microstructure of the clays in the nanocomposites was characterized by small-angle neutron scattering (SANS), ultra-small-angle neutron scattering (USANS), small-angle X-ray scattering (SAXS), and high-resolution transmission electron microscopy (HR-TEM). All clays were highly delaminated and well dispersed within their host matrixes. The mean number of individual clay platelets per tactoid was predicted by fitting SANS data to the stacked-disk model and measured directly from HR-TEM images of a large number of tactoids in each sample. SANS results were in good agreement with HR-TEM for composites with low clay concentrations (0.5 wt%); however, deviations were observed at higher clay loadings (2.0 wt%). These deviations are discussed in terms of several factors not taken into account by the stacked-disk model: (a) long-range interactions, which become more important at high loadings; (b) departure of tactoid geometries from parallel stacks of rigid disks; and (c) the polydispersity of tactoid thicknesses. SAXS peaks were not present for most of the synthesized nanocomposites, suggesting a high degree of clay delamination was achieved. However, a broad peak was observed for the 2.0 wt% I-44pa clay nanocomposite, indicating the presence of some larger tactoids than in the other nanocomposites having a range of d-spacings. The HR-TEM measured distributions of clay platelet d-spacings in tactoids dispersed within the nanocomposites which were in the range from 8 to 20 Å (12−15 Å average), indicating that the quaternary ammonium ion pillaring agents were no longer present. These quaternary salts either decomposed during the high-temperature (260 °C) stage of curing or were not fully exchanged with the interlayer cations present between all platelet interlayers during the original clay modification. Clay/polyDCPD composites were also prepared using PGW clay modified by poly(ethylene glycol). This clay dispersed more rapidly, needing less sonication than the other clays. The resistance to delamination of all nanocomposites studied increased with greater clay loading under equivalent synthesis conditions.

Structure Investigation of Metal Ions Clustering in Dehydrated Gel Using X-ray Anomalous Dispersion Effect

The structure of copper ion clusters in dehydrated N-isopropylacrylamide/sodium acrylate (NIPA/SA) gel has been studied by means of small angle X-ray scattering (SAXS) method. In order to distinguish the intensity scattered by Cu ions, the X-ray anomalous dispersion effect around the Cu K absorption edge has been coupled with SAXS. It is found that the dispersion effect dependent on the incident X-ray energy is remarkable only at the momentum transfer q =0.031 Å -1 , where a SAXS peak is observed. The results indicate that copper ions form clusters in the dehydrated gel, and that the mean size of clusters is the same as that of SA clusters produced by microphase separation.It is therefore naturally presumed that copper ions are adsorbed into the SA molecules. On the basis of the presumption, a mechanism is proposed for microphase-separation and clustering of Cu ions.

Nanostructure Evolution of Homogeneous Poly(ethylene‐co‐1‐octene) as a Function of Strain

AbstractPolyolefin elastomers with varying 1‐octene content and different thermal history are studied by wide‐angle X‐ray scattering (WAXS) and small‐angle X‐ray scattering (SAXS) during drawing and after relaxation. The multidimensional chord distribution function (CDF) reveals the nanostructure made from crystallites in the amorphous matrix. Both lamellae and granular crystals are found. Lamellae do not form stacks. The SAXS peak is observed because each lamella is covered by an amorphous layer of well‐defined thickness. Arrangement, rotation, fine chain slip and failure of the domains are directly observed as a function of elongation. During straining and relaxation a well oriented macrolattice with colloidal dimensions but short‐ranging order is formed. Two processes are generating microfibrils, namely (1) arrangement of granular crystallites, and (2) irreversible disruption of lamellae (coarse slip) followed by arrangement of their fragments. The second process stabilizes the colloidal lattice permanently. The higher the comonomer content, the later the irreversible process starts. Quenching from the melt shifts the onset to lower deformation. Deformation of microfibrils is not homogeneous. Instead, there is a limiting long period that cannot be exceeded without disruption. It is related to the position of the maximum in the SAXS pattern (which is almost constant).Long periods in the CDF z(r12, r3) of an ethylene‐octene block copolymer after relaxation from drawing.magnified imageLong periods in the CDF z(r12, r3) of an ethylene‐octene block copolymer after relaxation from drawing.

Long periods in oriented semicrystalline polymers at low temperatures

The reflection peak intensity in the small-angle X-ray scattering (SAXS) curves of oriented semicrystalline isotactic poly(propylene) and low-density poly(ethylene) films exhibits a reversible severalfold decrease upon cooling the samples to −90°C. At the same time, the other supermolecular structure parameters (long periods and the longitudinal dimensions of crystallites and amorphous regions, etc.) remain unchanged. The observed reversible SAXS peak intensity variations are explained by the fact that a part of the polymer chains penetrate from inter-to intrafibril (amorphous) regions or return back into the interfibril (crystalline) regions.

Equilibrium short-range order in the isotropic phase of a poly(ester-imide) with a C22H44 alkane spacer

Small-angle X-ray scattering (SAXS) was performed on a sample of poly(4,4′- phthaloimidobenzoyldoeicosamethyleneoxycarbonyl) (PEIM-22) as a function of temperature. Wide-angle X-ray diffraction and differential scanning calorimetry were used to follow the isotropization of the crystalline PEIM-22. The crystals of PEIM-22 consist of biphasic layers up to the isotropization temperature. A series of SAXS peaks are observed for the crystals between θ = 0.3 and 3.5°. The width of these peaks indicates the formation of a smectic-like, crystalline layer structure of a coherently scattering domain size of only 3–4 repeating units. In the isotropic phase, a single, broader peak remained at a spacing of ≈2.6 nm, suggesting even at high temperature the existence of equilibrium, short-range, local order. The SAXS profiles were calculated based on a model of alternating layers of a linear, paracrystalline lattice. The results were discussed together with similar data on model compounds in the literature, and it is suggested that the short-range order in the isotropic phase is due to a nanometer-scale separation of the polar, aromatic phthaloimidobenzoyl from the flexible doeicosamethyleneoxycarbonyl. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 611–621, 2000

Small-Angle X-ray Scattering Study of the Microphase Separation Transition in Asymmetric Diblock Copolymers: A Model “B” Kinetic Phenomenon

We report the results of a time-resolved small-angle X-ray scattering (SAXS) study of the kinetics of the microphase separation transition in asymmetric styrene−butadiene diblock copolymers in semidilute solution. Following a quench to below the transition temperature, the scattered intensity at early stages is found to increase exponentially with time according to a time-dependent Ginzburg−Landau (TDGL) model, model “B” in the Hohenberg−Halperin notation. Over a range of scattering vectors near the SAXS peak, the exponential rate constants are modeled using the TDGL theory. The form of the wavevector dependence of the measured rate constants is used to test the fundamental predictions of the TDGL model. No lower and upper critical wavevectors are identified, although valid results for the static parameters are provided within the context of the model.

Order ‐ disorder transitions in comb‐like polymer‐surfactant systems involving hydrogen bonds

AbstractConditions to obtain micro‐phase separated morphologies in polymer‐surfactant systems involving hydrogen bonds have been investigated using poly(4‐vinyl pyridine) (P4VP) and surfactants capable of forming hydrogen bonds of different strength with the basic nitrogen of P4VP. Depending on the tail length, the hydrogen bonding strength, the amount of surfactant and the temperature, four different regimes have been identified: I. Micro‐phase separated state, II. Homogeneous state exhibiting a distinct Small Angle X‐ray Scattering (SAXS) peak, III. Homogeneous state without a SAXS peak and, IV. Macro‐phase separated state. Time‐resolved SAXS / W(ide) A(angle) X(ray) S(cattering) / D(ifferential) S(canning) C(alorimetry) as well as rheological measurements are used to identify the different regimes. A simplified model description together with preliminary computer simulation results are presented.

Investigation of the structure and properties of polyisobutylene-based telechelic ionomers of narrow molecular weight distribution. I.

The solid state morphology of recently developed sulfonated polyisobutylene (PIB) telechelic ionomers with narrow molecular weight distribution (MWD) (M¯w/M¯n ≈ 1.15) was investigated. A small angle X-ray scattering (SAXS) peak often associated with the aggregation of the ionic species in the bulk, as well as a secondary peak, have been observed in the narrow distribution sulfonated PIB telechelic ionomers for the first time. Ionomers of difunctional and tri-arm architecture at several number average molecular weights (M¯n) with one of several counterions were investigated and the preparation method was also considered in terms of observed SAXS behavior. Compression-molded films made from these narrow MWD telechelics were examined in detail using SAXS. Primary and secondary peaks were observed in the slit-smeared SAXS profiles up to an M¯n of 27 kg/mol. The ratio of the interdomain spacings derived from these peaks (ca. 2 : 1) suggests cylindrical or lamellar ordering in the morphology in both difunctional and tri-arm ionomers. Pinhole SAXS images showed no azimuthal dependence in the scattering pattern and thus, this ordering is on a local scale. It was found that the counterion has an inconsistent effect on the smeared interdomain spacing associated with the SAXS peak. The smeared interdomain spacings were systematic with respect to architecture and M¯n for solution cast Cs+ ionomers. The difunctional telechelics exhibited higher smeared interdomain spacings than tri-arms of comparable M¯n and unlike the compression-molded films, the smeared interdomain spacings of the solution cast Cs+ telechelic ionomers increased systematically with increasing M¯n. Even a broad MWD (M¯n/M¯n ≈ 1.8) tri-arm telechelic ionomer M¯n of 20.6 kg/mol exhibited a diffuse primary peak in SAXS when solution-cast. However, it exhibited no peak when compression-molded. © 1997 John Wiley & Sons, Inc.

Crystallization behaviour and morphological features of LARC-CPI

This work describes the crystallization behaviour and morphological features of the semicrystalline polyimide known as LARC-CPI. The study considers several features affecting crystallization behaviour such as inherent viscosity, crystallization temperature, melt temperature and time in the melt. Crystallization kinetics data were analysed using an Avrami analysis in conjunction with differential scanning calorimetry. Complications encountered when evaluating the crystallization exotherm for this analysis are also discussed. Morphological features were investigated using several techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), wide-angle X-ray scattering (WAXS), and small-angle X-ray scattering (SAXS). A permanganic etching technique combined with SEM successfully revealed morphological detail further supported by TEM results. This technique is also used to estimate the isothermal linear crystalline growth rate, G. The SEM and TEM data lend support to the Avrami data obtained by crystallization kinetics. SAXS results reflect the influence of crystallization temperature on the long spacing. SAXS also reveals the presence of a broad second scattering peak for semicrystalline samples which appears in the same position regardless of crystallization temperature or inherent viscosity. Molecular modelling predicts a low-energy helical conformation with a near-periodic repeat distance corresponding to that of the second SAXS peak. The periodic character of this conformation is offered as a hypothesis for that peak. This work also considers the effect of potential nucleating agents on the recrystallizability of a higher inherent viscosity LARC-CPI. One of the several nucleators investigated appears effective in enhancing the bulk crystallization rate.

Small Angle X-Ray Scattering on Poly(Ethylene-Methacrylic Acid) Lead and Lead Sulfide Ionomers

ABSTRACTThe morphology of ionomers, e.g., poly(ethylene-methacrylic acid) (EMA) lead salts (EMA/Pb) and lead sulfide compounds (EMA/PbS), has been studied by using the techniques of small angle x-ray scattering (SAXS), anomalous SAXS (ASAXS), wide angle x-ray scattering (WAXS), and differential scanning calorimetry (DSC). EMA/Pb containing less than 5 wt% of lead exhibited two characteristic SAXS peaks which corresponded to the lamellar structure of the partially crystalline polymer matrix and the ionic structure of the lead aggregates that were present in the amorphous regions. The lead aggregates were not distributed uniformly and increased in packing density with increasing lead content. Both DSC and WAXS showed that the crystalline phase was present for all EMA/Pb samples and that the crystallinity decreased slightly with increasing lead content. ASAXS near the L3 absorption edge of lead permitted the extraction of the scattered intensity of lead ions from the SAXS patterns of the superimposed crystalline and ionic structures. Correlation function analysis revealed that the ionic aggregates of the EMA/Pb containing 5 wt% of lead could be described by a liquid-like model with a short range order of 2-4 nm. EMA/PbS samples were made by a reaction of EMA/Pb ionomers with hydrogen sulfide. Instead of an ionic peak as shown by EMA/Pb samples, the SAXS patterns of EMA/PbS showed a broad diffraction peak located at the same q value as the lamellar peak of the EMA in acid form. The (lamellar) peak could be attributed to the interference between the PbS crystallites in the neighboring lamellae.

The effect of lintnerisation on wheat and potato starch granules

Wheat and potato starches were hydrolysed with 2·2 n hydrochloric acid at 35°C for a period of time up to 15 days. The residues (lintnerised starches) were washed and freeze dried, and studied by differential scanning calorimetry (DSC), wide-angle X-ray scattering (WAXS), small-angle light scattering (SALS), small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS). These techniques showed that profound changes took place in the first day of hydrolysis (during which time the extent of hydrolysis was 7·7% for potato starch and 12·5% for wheat starch). In particular, the gelatinisation enthalpy (ΔH) decreased, the X-ray crystallinity increased and the SANS and SAXS peaks (indicative of a regular spacing between crystalline and amorphous regions) virtually disappeared. The reduction in ΔH is surprising and is discussed at length. It was also shown that freeze drying results in a considerable lowering of the gelatinisation temperature of potato starch (and also of ΔH) while that of wheat starch is only slightly affected.