Recent developments in polymer applications of synchrotron small‐angle X‐ray scattering

Synchrotron radiation facilities have been established and become very familiar in the polymer community not only from academic but also industrial viewpoints. It is not so unusual now to conduct simultaneous measurements of small‐angle X‐ray scattering (SAXS) with other techniques such as wide‐angle X‐ray scattering, stress–strain, light scattering, and so forth. New techniques have also been established and have become more familiar in recent years. In this review, recent developments in polymer applications of synchrotron SAXS are summarized. Instrumental developments and progress in data analyses are reviewed from the following aspects: ultra‐small‐angle X‐ray scattering, anomalous SAXS, X‐ray photon correlation spectroscopy, new types of simultaneous measurements, grazing‐incidence SAXS, new trends in nanoparticle analyses and industrial applications. © 2016 Society of Chemical Industry     

Microfocus small‐angle X‐ray scattering investigation of the skin–core microstructure of lyocell cellulose fibers

Skin–core microstructures in hydrated lyocell cellulose fibers were investigated using microfocus small‐angle X‐ray scattering (SAXS). Both single fibers and fiber cross sections were observed. In all the fibers studied, a thin skin layer was observed in which the voids were smaller in cross section and better oriented than those in the core. The division between skin and core may not be sharp. A draw ratio of 0.80 gave fibers with voids that were shorter, larger in cross section, and more misoriented than the fibers produced with a draw ratio of 1.68. In contrast, there was little difference in void structure between samples coagulated in water and in 25% amine oxide aqueous solution. The results are explained in the context of the spinodal decomposition, which is thought to occur during coagulation. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2799–2816, 2002; DOI 10.1002/app.10256     

Physicomechanical,optical, barrier,and wide angle X‐ray scattering studies of filled low density polyethylene films

Series of low density polyethylene (LDPE) films filled with different fillers such as silica, mica, soya protein isolate, potassium permanganate, and alumina were processed using a single screw extruder. The filled LDPE films were characterized for physicomechanical properties like tensile strength, percentage elongation at break, and tear strength, optical properties like percent transmission and haze. The barrier properties such as water vapor transmission rate and oxygen transmission rate of the filled LDPE films have also been reported. Microcrystalline parameters such as crystal size (〈N〉) and lattice distortion (g) of the filled LDPE films obtained using wide angle X‐Ray scattering method have been reported. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2781–2789, 2006     

About the Lorentz correction used in interpretation of small‐angle X‐ray scattering data of semicrystalline polymers

Lorentz correction is used to correct the intensities of X‐ray scattering of single‐crystal diffractometry in order to recalculate intensities to obtain structure factors. This correction reduces the intensities to zero at zero diffraction angle. Small‐angle scattering is used to study the dimensions of heterogeneities in polymeric materials. The scattering intensities at a near to zero scattering angle originate partly from periodic systems (reciprocal lattice) and partly from dispersed particle systems. Periodic systems should result in individual Gaussian or Lorentzian peaks with the position of a peak maximum depending on the length of the periodicity. Particle scattering results in a Gaussian peak centered at zero scattering angle. The effect of the Lorentz correction on the interpretation of small‐angle X‐ray scattering data is shown for some semicrystalline polyethylenes (high‐density, linear low‐density, and low‐molecular‐weight waxy polyethylenes). The data are compared to those for amorphous block copolymers (styrene–butadiene), in which there is a periodic system with homogeneous lamellar thickness. Lorentz correction destroys the characteristics of the particle scattering and can be applied only for periodic systems. It should not be used to produce a peak on scattering data, which do not show periodicity (peaks) without correction. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 358–366, 2001     

Thermal and wide angle X‐ray analysis of chemically and radiation‐crosslinked low and high density polyethylenes

Low and high density polyethylenes (PE) were crosslinked by two methods, namely, chemically by use of different amounts of tert‐butyl cumyl peroxide (BCUP) and by irradiation with different doses of electron beam. A comparison between the effects of these two types of crosslinking on crystalline structure, crystallinity, crystallization, and melting behaviors of PE was made by wide angle X‐ray diffraction and DSC techniques. Analysis of the DSC first heating cycle revealed that the chemically induced crosslinking, which took place at melt state, hindered the crystallization process and decreased the degree of crystallinity, as well as the size of crystals. Although the radiation‐induced crosslinking, which took place at solid state, had no significant influence on crystalline region, rather, it only increased the melting temperature to some extent. However, during DSC cooling cycle, the crystallization temperature showed a prominent decrease with increasing irradiation dose. The wide angle X‐ray scattering analysis supported these findings. The crystallinity and crystallite size of chemically crosslinked PE decreased with increasing peroxide content, whereas the irradiation‐crosslinked PE did not show any change in these parameters. As compared with HDPE, LDPE was more prone to crosslinking (more gel content) owing to the presence of tertiary carbon atoms and branching as well as owing to its being more amorphous in nature. HDPE, with its higher crystalline content, showed relatively less tendency toward crosslinking especially by way of irradiation at solid state. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3264–3271, 2006     

Electrical,physicomechanical, and X‐ray studies on ethylene‐vinyl acetate copolymer/polyaniline blends

The conductive blend consisting of ethylene‐vinyl acetate (EVA) and a polyaniline/p‐toluene sulfonic acid (PAn/TSA) complex were prepared by a thermal doping process using a Brabender plasticorder at 150°C. The conductivity, dielectric constant, dissipation factor, mechanical behavior, and structural aspects of these blends were investigated. A higher percentage of the PAn/TSA complex in the EVA matrix resulted in an increase in the electrical properties and a decrease in the mechanical properties like the tensile strength and percentage of elongation. These results were compared with the microcrystalline parameters of the blend obtained from X‐ray profile analysis. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1730–1735, 2002     

Small‐angle X‐ray scattering investigation of the deformation processes in the amorphous phase of high density polyethylene

In situ small‐angle X‐ray scattering of high density polyethylene under uni‐axial tensile test was used for investigating the deformation at the scale of the periodic crystalline–amorphous nano‐structure. The more or less uniform elastic straining of the rubbery amorphous layers is discussed in terms of mechanically active intercrystalline tie chains. Correlation is made with the long‐term use properties. It is concluded that this approach is a powerful means to assess the mechanical efficiency of tie molecules. Copyright © 2004 Society of Chemical Industry     

A Shielding Topology Stabilizes the Early Stage Protein–Mineral Complexes of Fetuin‐A and Calcium Phosphate: A Time‐Resolved Small‐Angle X‐ray Study

Biomineralization mechanisms : The serum protein α₂‐HS glycoprotein/fetuin‐A is an important inhibitor that prevents pathological mineralization of calcium phosphate in soft tissues and in the extracellular fluid. TR‐SAXS and stopped‐flow analysis were used to monitor the growth of protein mineral particles nucleating from supersaturated salt solutions in the presence of the protein. It was found that fetuin‐A did not influence the formation of mineral nuclei, but did prevent the aggregation of nuclei and thus mineral precipitation.

     

About the Lorentz correction used in the interpretation of small angle X‐ray scattering data of semicrystalline polymers

Lorentz correction is used to correct the intensities of X‐ray scattering of single crystal diffractometry in order to recalculate intensities to obtain structure factors. This correction reduces the intensities to zero at zero diffraction angle. Small angle scattering is used to study the dimensions of heterogeneities in polymeric materials. The scattering intensities near to zero scattering angle originate partly from periodic systems (reciprocal lattice) and partly from dispersed particle systems. Periodic systems should result in individual Gaussian or Lorentzian peaks with the position of a peak maximum depending on the length of the periodicity. Particle scattering results in a Gaussian peak centred at zero scattering angle. The effect of the Lorentz correction on the interpretation of small angle X‐ray scattering data is shown in the case of some semicrystalline polyethylenes (high density, linear low density, and low molecular weight waxy polyethylenes). The data are compared with those for amorphous block copolymers (styrene/butadiene) in which there is a periodic system with homogeneous lamellar thickness. Lorentz correction destroys the characteristics of the particle scattering and can be applied only for periodic systems. It should not be used to produce a peak on scattering data which does not show periodicity (peaks) without correction. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2300–2308, 2001     

A study of the morphology of polyurethane–polystyrene interpenetrating polymer networks by means of small angle X‐ray scattering,modulated‐temperature differential scanning calorimetry,and dynamic mechanical thermal analysis techniques

The morphology of polyurethane–polystyrene (PU‐PS) (60 : 40 by weight) interpenetrating polymer networks (IPNs), in which internetwork grafting via 2‐hydroxyethyl methacrylate resides (HEMA) (1, 2.5, and 10 wt %, respectively) in the polystyrene networks has been studied by means of small angle X‐ray scattering (SAXS), modulated‐temperature scanning calorimetry (M‐TDSC), and dynamical mechanical thermal analysis (DMTA) techniques. With increasing internetwork grafting, the average size of domains became smaller (SAXS data) and the degree of component mixing increased (M‐TDSC and DMTA results). For the PU‐PS (60 : 40 by weight) IPN with 10% HEMA, the DMTA tan δ‐temperature plot showed a single peak. This DMTA result implied that the morphology of this PU‐PS IPN is homogeneous. However, the M‐TDSC data showed that three PU‐PS (60 : 40) IPNs samples (with 1, 2.5, and 10 wt % HEMA, respectively) were phase separated. For the three IPN samples, the correlation length of the segregated phases, obtained from SAXS data based on the Debye–Bueche method, did not show distinct differences. With increasing internetwork grafting, the scattered intensity decreased. This study concluded that for these IPNs, SAXS is sensitive to the size of domains and component mixing, but no quantitative analysis was given for the component mixing. M‐TDSC is suitable to be used to quantify the degree of component mixing or the weight fraction of interphases, and DMTA is sensitive to damping behavior and to phase continuity. However, DMTA cannot provide quantitative information about the degree of component mixing or the weight (or volume) fraction of the interphases. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1958–1964, 2001     

Peak‐fitting analysis of cotton fiber powder X‐ray diffraction spectra

The precision and accuracy of diffraction peak positions resolved from the powder X‐ray diffraction spectra of cotton fibers by means of the residuals peak‐fitting procedure of a commercial peak‐fitting software package (PeakFit®) was investigated to explore the potential of such programs in providing reliable data that are not readily apparent in diffuse X‐ray spectra. Each intensity spectrum was fitted by employing a Gaussian function as the peak profile. The precision of 15 pairs of the resolved diffraction peaks is 0.0017 mm; 9 of the 15 pairs fall into the 99% confidence interval. The precision in 2θ of four commonly identified peaks through four independent fittings is from 0.002 to 0.014°. The 2θ accuracy of the resolved peaks is good in comparison to data calculated for both the traditionally accepted and the more recently revised concepts of the cellulose I crystal structure. A peak resolved at about 15.3° may be attributed to the triclinic crystal structure component of cellulose I. Although distinct peaks are not readily apparent in the diffuse spectrum of cellulose, peak‐fitting procedures may provide additional data for structure determination. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2019–2024, 2004     

Oligolactate‐grafted dextran hydrogels: Detection of stereocomplex crosslinks by X‐ray diffraction

Physically crosslinked hydrogels are formed upon mixing equal amounts of aqueous solutions of dextran grafted with L ‐lactic acid oligomers and dextran grafted with D ‐lactic acid oligomers. In this paper, the dex‐lactate hydrogels are analyzed by X‐ray diffraction to provide evidence that hydrogel formation occurred through stereocomplex formation. First, the stereocomplex formation of monodisperse lactic acid oligomers was studied and comparison with published results of poly(lactic acid) was made. It was clearly demonstrated that stereocomplexes were formed between oligomers of opposite chirality. The data for these monodisperse lactic acid oligomers were used to interpret the results obtained with the dex‐lactate hydrogels. X‐ray diffraction measurements demonstrated that in the hydrogels stereocomplexes were formed between the lactic acid oligomers of opposite chirality. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 289–293, 2002     

Fibrous long‐chain organic acid cellulose esters and their characterization by diffuse reflectance FTIR spectroscopy,solid‐state CP/MAS 13C‐NMR,and X‐ray diffraction

Unsaturated and saturated organic acids with 11 and 18 carbon atoms, respectively, were used in a heterogeneous esterification reaction in the pyridine/toluene sulfonyl chloride system to prepare fibrous cellulose esters with different degrees of substitution. Highly bleached sulfite cellulose fibers were esterified during a 1‐ or 2‐h reaction time with the following organic acids: undecylenic acid, undecanoic acid, oleic acid, and stearic acid. In all cases, the heterogeneous esterification yielded partially substituted cellulose esters retaining their fibrous structure. The substitution reaction was confirmed by diffuse reflectance infrared spectroscopy and the chemical structures of cellulose esters were identified by solid‐state CP/MAS ¹³C‐NMR (75.3 MHz). X‐ray diffraction analyses showed broadening of the diffraction peaks with a higher degree of substitution of cellulose esters, which suggests structural changes within the cellulose fibers. Because the broadening peaks of X‐ray spectra or the unassigned C‐4 region of substituted cellulose chains in NMR spectra do not allow the calculation of dimensional changes of cellulose crystallites in cellulose esters, the lateral dimensions of crystallites in only cellulose fibers were calculated. The value derived from NMR (4.6 nm) differs by about 11% when compared with the value calculated from X‐ray diffraction data (4.1 nm). © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1354–1365, 2000     

X‐ray diffraction studies on reverse‐annealed polyethylenes

Linear low and high density polyethylene sheets were compression molded and crystallized at a 5–10°C/min cooling rate. Parts of the sheets were annealed at different temperatures up to 2°C below the melting temperature. The small angle X‐ray scattering (SAXS) and the wide angle X‐ray scattering intensities of the annealed samples were studied. SAXS intensities showed particle scattering with a bimodal size distribution. The estimated radii of gyration were 15–17 nm and 5–7 nm, respectively. The crystallinity and the radius of gyration increased slightly with increasing annealing temperature for some samples; others did not show any change. No peaks characteristic of intercorrelated lamellar crystallinity in the SAXS intensities developed during the annealing. The original broad peak of high density polyethylene disappeared from the SAXS recordings on annealing. The length of the perfect chain versus melting temperature was calculated by the Thomson‐Gibbs formula and Flory's concept of melting temperature depression where methyl groups and tertiary carbon atoms at the branches were regarded as second components (solvent). Linear relationships were found for both cases. Experimental data for a linear low density polyethylene obtained from the literature were in between the two functions. A lamellar model of crystallization corresponding to the data is proposed. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 340–349, 2001     

Sillimanite‐mullite transformation observed in synchrotron X‐ray diffraction experiments

High‐resolution synchrotron powder X‐ray diffraction (XRD) experiments were conducted to clarify the transformation of sillimanite to mullite (mullitization) and determine the mullitization temperature (T_c). We were able to distinguish sillimanite and mullite in the XRD patterns, despite their very similar crystallographic parameters, and to detect the appearance of small mullite peaks among sillimanite peaks. Analysis of the Johnson‐Mehl‐Avrami (JMA) equation for mullitization ratio (ζ) revealed that at temperatures T≥1240°C the mullitization had the same kinetics. The activation energy E at T≥1240°C obtained from the Arrhenius plot was 679.8 kJ mol^?1. In analysis using a time‐temperature‐transformation diagram for mullitization, a mullitization curve of ζ=1% can be described as where t is time, n is a reaction‐mechanism‐dependent parameter determined as 0.324 by JMA‐analysis, k₀ is the frequency factor, E_A is the activation energy for atomic diffusion, and represents the activation energy for nucleation. The results of fitting the data to this equation were T_c=1199°C, A=3.9×10⁶ kJ mol^?1 K^?2, E_A=605 kJ mol^?1, and k₀=3.65×10¹⁵. We conclude that the boundary between sillimanite and mullite+SiO₂ in the phase diagram is ~1200°C.     

Uniaxially aligned poly[(9,9‐dioctylfluorenyl‐2,7‐diyl)‐co‐bithiophene] thin films characterized by the X‐ray diffraction pole figure technique

Aligned thin films of the liquid‐crystalline polymer poly[(9,9‐dioctylfluorenyl‐2,7‐diyl)‐co‐bithiophene] were prepared, and the correlation between the optical anisotropy and the structural properties was shown. A series of samples with different thicknesses were prepared via a spin‐casting process on rubbed polyimide surfaces. The alignment of the polymer chains was obtained by a temperature treatment just below the clearing temperature. The degree of alignment was investigated with ultraviolet–visible absorption spectroscopy and in‐plane X‐ray diffraction. Independently, each technique revealed Hermans orientation functions in the range of 0.75–0.8. Surprisingly, a layer‐thickness dependence was not observed. In addition, the X‐ray diffraction pole figure technique revealed that the polymer chains were uniaxially aligned along the rubbing direction. The aligned films were in the nematic state, with the director elongated along the rubbing direction. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

On the fractal character of polymer spherulites: an ultra‐small‐angle X‐ray scattering study of poly[(R)‐3‐hydroxybutyrate]

Ultra‐small‐angle X‐ray scattering (USAXS) and small‐angle X‐ray scattering (SAXS) measurements are presented for poly[(R)‐3‐hydroxybutyrate] (PHB) crystallized at room temperature. The USAXS patterns indicated that the spherulites had a radially orientated fibrillar nanostructure with fractal geometry over a length scale ranging from 12 nm up to at least 300 nm, with a mass fractal dimension of approximately 2.7 in aged samples. The SAXS patterns indicated that the fibrils themselves were built up of bundles of crystalline lamellae separated by layers of disordered material, with a period length of approximately 6 nm. The SAXS measurements during primary crystallization gave an initial fractal dimension of 4 during spherulite growth, due to the sharp phase boundary between the spherulites and the melt. Copyright © 2004 Society of Chemical Industry     

Borate melt structure: Temperature‐dependent B–O bond lengths and coordination numbers from high‐energy X‐ray diffraction

Borate melts containing <20 mol% Na₂O have been studied using high‐energy synchrotron X‐ray diffraction. Temperature dependencies of the mean B–O bond lengths are shown to vary strongly with soda content, by comparison to previous measurements on liquid B₂O₃ and Na₂B₄O₇. Whereas in liquid B₂O₃ linear thermal expansion of the BØ₃ units is observed, with coefficient α_BO = 3.7(2) × 10^?6 K^?1, this expansion is apparently slightly suppressed in melts containing <20 mol% Na₂O, and is dramatically reversed at the diborate composition. These effects are interpreted in terms of changes in the mean B–O coordination number, where the reaction BØ₄^? + BØ₃ ? BØ₃ + BØ₂O^? shifts to the right with increasing temperature. The empirical bond‐valence relationship is used to convert measured bond lengths, r_BO, to coordination numbers, n_BO, including a correction for the expected thermal expansion. This method is more accurate and precise than direct determination of n_BO from peak areas in the radial distribution functions. Gradients of Δn_BO/ΔT = ?3.4(3) × 10^?4 K^?1 close to the diborate composition, and Δn_BO/ΔT = ?0.3(1) × 10^?4 K^?1 for a 13(3) mol% Na₂O melt are observed, in reasonable agreement with Raman spectroscopic observations and thermodynamic modeling, with some quantitative differences. These observations go toward explaining isothermal viscosity maxima and changes in fragility across the sodium borate system.     

Pressure‐Sensitive Adhesive Blend Films for Low‐Tack Applications

Polymer blend films consisting of a tacky and a nonadhesive component are promising candidates for low‐tack applications. Immiscibility of both components results in a phase separation process yielding a tacky matrix with glassy objects embedded. The influence of the blending ratio of the components poly(n‐butyl acrylate) (PnBA) and polystyrene (PS) is addressed. The mechanical information resulting from the tack test shows the possibility of varying the bonding strength of the PSA blend over a wide range. The macroscopic and microscopic structural characterization with optical microscopy and ultrasmall angle X‐ray scattering (USAXS) shows that the blend PnBA/PS exhibits similarities to common filler systems as well as deviates regarding installed structures. Due to the large domain size on a microscopic level, only the tacky component, PnBA, defines the adhesive behavior. The nonadhesive component limits the contact area between the adhesive and the substrate.

     

Study of the degree of crystallinity in eudragit/poly(methyl methacrylate) polyblends by X‐ray diffraction

Plaques of blends of Eudragit RL 100 (EU) and poly(methyl methacrylate) (PMMA) with different weight‐per‐weight ratios were prepared by compression molding at 150°C. The X‐ray diffraction profiles of the blends were studied and compared, and the interplanar distance, crystallite size, and crystallinity were computed for various peaks. The Eu/PMMA blend with a 70:30 (w/w) ratio had the maximum crystallinity. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1835–1838, 2005