Watching Nanoparticles Form: An In Situ (Small‐/Wide‐Angle X‐ray Scattering/Total Scattering) Study of the Growth of Yttria‐Stabilised Zirconia in Supercritical Fluids

Understanding nanoparticle‐formation reactions requires multi‐technique in situ characterisation, since no single characterisation technique provides adequate information. Here, the first combined small‐angle X‐ray scattering (SAXS)/wide‐angle X‐ray scattering (WAXS)/total‐scattering study of nanoparticle formation is presented. We report on the formation and growth of yttria‐stabilised zirconia (YSZ) under the extreme conditions of supercritical methanol for particles with Y₂O₃ equivalent molar fractions of 0, 4, 8, 12 and 25 %. Simultaneous in situ SAXS and WAXS reveals a quick formation (seconds) of sub‐nanometre amorphous material forming larger agglomerates with subsequent slow crystallisation (minutes) into nanocrystallites. The amount of yttria dopant is shown to strongly affect the crystallite size and unit‐cell dimensions. At yttria‐doping levels larger than 8 %, which is known to be the stoichiometry with maximum ionic conductivity, the strain on the crystal lattice is significantly increased. Time‐resolved nanoparticle size distributions are calculated based on whole‐powder‐pattern modelling of the WAXS data, which reveals that concurrent with increasing average particle sizes, a broadening of the particle‐size distributions occur. In situ total scattering provides structural insight into the sub‐nanometre amorphous phase prior to crystallite growth, and the data reveal an atomic rearrangement from six‐coordinated zirconium atoms in the initial amorphous clusters to eight‐coordinated zirconia atoms in stable crystallites. Representative samples prepared ex situ and investigated by transmission electron microscopy confirm a transformation from an amorphous material to crystalline nanoparticles upon increased synthesis duration.     

Wide and small-angle X-ray scattering study of isotactic polypropylene gamma irradiated in bulk

Gamma irradiated isotactic polypropylene (IPP) has been studied by means of wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS). The skin layer has been investigated by WAXS reflection mode while the core layer underwent WAXS studies by transmission mode. β-IPP has been found solely in the skin layer. An increase in the β-phase has been observed as result of the irradiation. A phase transitions and decrease of crystallite sizes have been also observed. All of the parameters show a sharp change at a critical dose of 100 kGy. At this point the system parameters reverse. Radiation processes proceeding up to 100 kGy called radiation annealing are related to the improved crystallite perfection and thus emphasize the phase boundary. The processes provoke at higher radiation doses, up to 2000 kGy, damage in both crystal and amorphous lamellar parts. The values of the crystal and amorphous densities get closer and the process is similar to the partial radiation melting.     

The microstructure of poly(vinyl chloride) as revealed by x-ray and light scattering

Small-angle x-ray scattering (SAXS) and wide-angle x-ray scattering (WAXS) as well as small-angle light-scattering (SALS) techniques have been applied to investigate the microstructure of a number of commercial poly(vinyl chloride) (PVC) samples. From the wide-angle x-ray scattering, crystallinity and crystal size parameters have been determined. The crystallinity of the samples investigated range from 5% to 10%. Superstructure parameters such as crystallite thickness, distribution functions of crystallite and amorphous thicknesses, and size of ordered regions have been obtained by an analysis of the SAXS curves using the cluster model. The crystallinity agrees well with the WAXS crystallinities indicating that most of the crystals are lamellar shaped, though some rodlike entities are present in the sample as is shown by the small-angle light scattering. From the SAXS analysis, the microstructure is described as clusters of lamella stacks which are identical with the subprimary particles. Their size is determined to be 220–240 Å. Emulsion type PVC also contains lamellar-shaped crystals. The superstructure, however, of this type of PVC is different from that of mass or suspension-polymerized material. The SAXS curve does not reveal any correlation between the crystals.     

In Situ High‐Energy Synchrotron Radiation Study of Boehmite Formation,Growth, and Phase Transformation to Alumina in Sub‐ and Supercritical Water

Boehmite (AlOOH) nanoparticles have been synthesized in subcritical (300 bar, 350 °C) and supercritical (300 bar, 400 °C) water. The formation and growth of AlOOH nanoparticles were studied in situ by small‐ and wide‐angle X‐ray scattering (SAXS and WAXS) using 80 keV synchrotron radiation. The SAXS/WAXS data were measured simultaneously with a time resolution greater than 10 s and revealed the initial nucleation of amorphous particles takes place within 10 s with subsequent crystallization after 30 s. No diffraction signals were observed from Al(OH)₃ within the time resolution of the experiment, which shows that the dehydration step of the reaction is fast and the hydrolysis step rate‐determining. The sizes of the crystalline particles were determined as a function of time. The overall size evolution patterns are similar in sub‐ and supercritical water, but the growth is faster and the final particle size larger under supercritical conditions. After approximately 5 min, the rate of particle growth decreases in both sub‐ and supercritical water. Heating of the boehmite nanoparticle suspension allowed an in situ X‐ray investigation of the phase transformation of boehmite to aluminium oxide. Under the wet conditions used in this work, the transition starts at 530 °C and gives a two‐phase product of hydrated and non‐hydrated aluminium oxide.     

Investigation of structural changes in semi-crystalline polymers during deformation by synchrotron X-ray scattering

The mechanical behavior of polymer materials is strongly dependent on polymer structure and morphology of the material. The latter is determined mainly by processing and thermal history. Temperature-dependent on-line X-ray scattering during deformation enables the investigation of deformation processes, fatigue and failure of polymers. As an example, investigations on polypropylene are presented. By on-line X-ray scattering with synchrotron radiation, a time resolution in the order of seconds and a spatial resolution in the order of microns can be achieved. The characterization of the crystalline and amorphous phases as well as the study of cavitation processes were performed by simultaneous SAXS and WAXS. The results of scattering experiments are complemented by DSC measurements and SEM investigations. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1574–1586, 2010     

Microfibril diameter in celery collenchyma cellulose: X-ray scattering and NMR evidence

Cellulose isolated from celery collenchyma is typical of the low-crystallinity celluloses that can be isolated from primary cell-walls of higher plants, except that it is oriented with high uniformity. The diameter of the microfibrils of celery collenchyma cellulose was estimated by three separate approaches: ¹³C NMR measurement of the ratio of surface to interior chains; estimation of the dimensions of the crystalline lattice from wide angle X-ray scattering (WAXS) measurements using the Scherrer equation; and the observation that microfibrils of this form of cellulose have the unusual property of packing into an irregular array from which small angle X-ray scattering (SAXS) shows features of both form and interference functions. The interference function contributing to the SAXS pattern implied a mean microfibril centre-to-centre distance of 3.6 nm, providing an upper limit for the diameter. However modelling of the scattering pattern from an irregular array of microfibrils showed that the observed scattering curve could be matched at a range of diameters down to 2.4 nm, with the intervening space more or less sparsely occupied by hemicellulose chains. The lateral extent of the crystalline lattice normal to the 200 plane was estimated as a minimum of 2.4 nm by WAXS through the Scherrer equation, and a diameter of 2.6 nm was implied by the surface: volume ratio determined by ¹³C NMR. The WAXS and NMR measurements both depended on the assumption that the surface chains were positioned within an extension of the crystalline lattice. The reliability of this assumption is uncertain. If the surface chains deviated from the lattice, both the WAXS and the NMR data would imply larger microfibril diameters within the range consistent with the SAXS pattern. The evidence presented is therefore all consistent with microfibril diameters from about 2.4 to 3.6 nm, larger than has previously been suggested for primary-wall cellulose. Some degree of aggregation may have occurred during the isolation of the cellulose, but the larger microfibril diameters within the range proposed are a consequence of the novel interpretation of the experimental data from WAXS and NMR and are consistent with previously published data if these are similarly interpreted.     

利用小角/广角X射线散射联用及一维相关函数分析研究聚(ε-己内酯)片晶的形态

用小角/广角X射线散射(SAXS/WAXS)联用的实验方法考察了等温结晶温度(Tc)和等温时间对聚(ε-己内酯)(PCL)片晶形态的影响.根据WAXS数据计算了PCL的重量结晶度,进而求得其体积结晶度Vc(WAXS).在不同Tc下结晶的PCL样品的Vc(WAXS)均略高于50%.对SAXS谱线做一维相关函数(1DCF)分析,得到了PCL的片晶长周期(LP)和无定形层厚度(La).通过比较WAXS及SAXS的数据分析结果,认为PCL晶体需用"三相模型"予以描述,其过渡层厚度(E)约为LP的15%～18%,对片晶形态具有重要影响.随着Tc升高,PCL晶体的Lc、La及E均逐渐增大,但Lc的变化率最大,这使得结晶度上升.在50℃等温结晶不同时间,发现Lc随延长时间显著增加,而La及E则不断减小.等温10天后,PCL晶体的SAXS谱线上可观察到5级散射,表明片晶相当完善.     

Multiaxial deformation of polyethylene and polyethylene/clay nanocomposites: in situ synchrotron small angle and wide angle X‐ray scattering study

A unique in situ multiaxial deformation device has been designed and built specifically for simultaneous synchrotron small angle X‐ray scattering (SAXS) and wide angle X‐ray scattering (WAXS) measurements. SAXS and WAXS patterns of high‐density polyethylene (HDPE) and HDPE/clay nanocomposites were measured in real time during in situ multiaxial deformation at room temperature and at 55 °C. It was observed that the morphological evolution of polyethylene is affected by the existence of clay platelets as well as the deformation temperature and strain rate. Martensitic transformation of orthorhombic into monoclinic crystal phases was observed under strain in HDPE, which is delayed and hindered in the presence of clay nanoplatelets. From the SAXS measurements, it was observed that the thickness of the interlamellar amorphous region increased with increasing strain, which is due to elongation of the amorphous chains. The increase in amorphous layer thickness is slightly higher for the nanocomposites compared to the neat polymer. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Microstructure rearrangement during the heat-treatment of melt-drawn poly(ethylene terephthalate) fibers

Melt-spun poly(ethylene terephthalate) fibers were isothermally heat-treated at constant length. Microstructural changes occurring during the heat-treatment were monitored using specific gravity, wide-angle x-ray scattering (WAXS), small-angle x-ray scattering (SAXS), optical birefringence, and static mechanical testing. Major changes in the density of the most highly oriented fiber examined occurred in times below 100 ms. For less oriented fibers, the time scale for significant density change increases to the 1–10 s range. The course of birefringence increase approximates that of the density. WAXS measurements show that crystallinity develops at essentially constant crystal perfection, but that the orientation of the crystallites first decreases and then increases with time. SAXS results show development of a four-point pattern, the azimuthal angle of the lobes decreasing with initial orientation, with temperature, and with time. A streak transverse to the fiber axis develops more rapidly than do the lobes. A two-stage transformation process is envisaged, the first stage being the formation of defective crystal fibrils and the second being internal rearrangement of the fibrils to form more perfect crystallites, separated by more amorphous zones. Changes in the crystallite orientation are related to constraints of the noncrystalline material on the crystallites.     

用SAXS/WAXS研究聚氧乙烯/聚氧丁烯嵌段共聚物在n-己烷中的结晶性球形胶束结构

嵌段共聚物在选择性溶剂中能够自组装形成胶束,胶束的不同形状与嵌段共聚物的结构、溶剂和浓度有关．无定形嵌段共聚物通常形成球形胶束,在某些情况下也可以形成其它形状的胶束,关于结晶性嵌段共聚物在无定形链段选择性溶剂中的胶束结构和形状的报道非常少．由于结晶和相似相溶两种作用力的竞争,使得这类胶束的形状丰富多变．通常结晶作用较强时,结晶性嵌段共聚物形成片状的胶束,当结晶组分比较少时,可形成棒状胶束,尽管理论上已经指出存在球形胶束,但尚无关于这方面的报道。     

Characterization of pore structure in metal-organic framework by small-angle X-ray scattering

MOF-5-like crystals were studied by small-angle X-ray scattering (SAXS) to reveal, both quantitatively and qualitatively, their real structural details, including pore surface characteristics, pore shape, size distribution, specific surface area (SSA), spatial distribution, and pore-network structure. A combined SAXS and wide-angle X-ray scattering (WAXS) experiment was conducted to investigate the variation of the pore structure with the MOF-5 crystalline phase produced at different cooling rates. The SSA of the MOF-5 crystals synthesized herein spanned a broad range from approximately 3100 to 800 m2/g. The real pore structures were divided into two regimes. In regime I the material consisted mainly of micropores of radius approximately 8 A as well as mesopores of radius 120 approximately 80 A. The structure in regime II was a fractal network of aggregated mesopores with radius >or=32 A as the monomer, reducing SSA and hydrogen uptake capacity at room temperature. The two regimes can be manipulated by controlling the synthesis parameters. The concurrent evolution of pore structure and crystalline phase during heating for solvent removal was also revealed by the in-situ SAXS/WAXS measurement. The understanding of the impact of the real pore structure on the properties is important to establish a favorable synthetic approach for markedly improving the hydrogen storage capacity of MOF-5.     

Phase transitions in poly(heptane-1,7-diyl biphenyl-4,4′-dicarboxylate). SAXS,WAXS and DSC study

The main-chain thermotropic liquid-crystalline poly(heptane-1,7-diyl biphenyl-4,4′-dicarboxylate) (P7MB) was investigated by time-resolved small-angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS), and differential scanning calorimerty (DSC). Nonisothermal crystallisation with different rates of cooling and heating was used. On cooling, two phase transitions are observed, isotropic melt - smectic (I-Sm) and Sm- three-dimensional crystalline structure (Sm-Cr), whereas on heating only one transition is observed, Cr-I transition. The transition enthalpies were calculated. Temperature dependences of d-spacings of all crystalline peaks and of the peak observed at high values of scattering vector in the SAXS region were derived. The temperature dependence of the degree of crystallinity was established, based on the integrated intensities of the crystalline peaks and amorphous halo in WAXS.     

In situ observation of homogeneous nucleation of nanosized zeolite A

The formation of zeolite A (LTA) in the presence of tetramethylammonium cations is studied using in situ small angle and wide angle X-ray scattering (SAXS/WAXS) techniques. The SAXS measurements show the formation of homogeneous precursors 10 nm in size prior to the crystallization of LTA which were consumed during the crystallization. The crystal size is estimated by fitting the SAXS patterns with an equation for a cubic particle, and it is revealed that the final crystal size of the LTA depends on the synthesis temperature. However, although such temperature dependence is noted for the final crystal size, the initial precursor particles size appears to be closely similar (ca. 10 nm) irrespective of the synthesis temperature.     

In situ SAXS/WAXS of zeolite microwave synthesis: NaY, NaA, and beta zeolites.

A custom waveguide apparatus is constructed to study the microwave synthesis of zeolites by in situ small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS). The WR-284 waveguide is used to heat precursor solutions using microwaves at a frequency of 2.45 GHz. The reaction vessels are designed to include sections of thin-walled glass, which permit X-rays to pass through the precursor solutions with minimal attenuation. Slots were machined into the waveguide to provide windows for X-ray energy to enter and scatter from solutions during microwave heating. The synthesis of zeolites with conventional heating is also studied using X-ray scattering in the same reactor. SAXS studies show that the crystallization of beta zeolite and NaY zeolite is preceded by a reorganization of nanosized particles in their precursor solutions or gels. The evolution of these particles during the nucleation and crystallization stages of zeolite formation depends on the properties of the precursor solution. The synthesis of NaA and NaX zeolites and sodalite from a single zeolite precursor is studied by microwave and conventional heating. Microwave heating shifts the selectivity of this synthesis in favor of NaA and NaX over sodalite; conventional heating leads to the formation of sodalite for synthesis from the same precursor. The use of microwave heating also led to a more rapid onset of NaA zeolite product crystallization compared to conventional heating. Pulsed and continuous microwave heating are compared for zeolite synthesis. The resulting rates of formation of the zeolite products, and the relative amounts of the products determined from the WAXS spectra, are similar when either pulsed or continuous microwave heating is applied in the reactor while maintaining the same synthesis temperature. The consequences of these results in terms of zeolite synthesis are discussed.     

In situ small-angle X-ray scattering analysis of palladium nanoparticle growth on tobacco mosaic virus nanotemplates

We present an examination of palladium (Pd) nanoparticle growth on genetically modified tobacco mosaic virus (TMV1cys) nanotemplates via in situ small-angle X-ray scattering (SAXS). Specifically, we examine the role of the TMV1cys templates in Pd nanoparticle formation through the electroless reduction of Pd precursor by a chemical reducing agent as compared to identical conditions in the absence of the TMV1cys templates. We show that in the presence of TMV1cys, the viral nanotemplates provide preferential growth sites for Pd nanoparticle formation, as no measurable Pd particle growth was observed in the bulk solution. In situ SAXS confirmed that particle formation was due to the rapid adsorption of Pd atoms onto the TMV1cys templates at the very early stage of mixing, rather than adsorption of particles formed in the bulk solution. Importantly, Pd nanoparticles were significantly smaller and more uniform as compared to particle formation in the absence of TMV1cys. The Pd nanoparticle coating density was tunable based on Pd precursor concentration. Finally, we show that Pd particle growth on the TMV1cys templates was highly rapid, and complete within 33 s for most samples, in contrast to slower Pd particle growth in the absence of TMV templates. We envision that the results presented here will be valuable in furthering the fundamental understanding of the role of viral nanotemplates in particle formation, as well as of their utility in a wide range of applications.     

Surface area and microporosity of carbon aerogels from gas adsorption and small- and wide-angle X-ray scattering measurements

A carbon aerogel was obtained by carbonization of an organic aerogel prepared by sol-gel polymerization of resorcinol and formaldehyde in water. The carbon aerogel was then CO(2) activated at 800 degrees C to increase its surface area and widen its microporosity. Evolution of these parameters was followed by gas adsorption and small- and wide-angle X-ray scattering (SAXS and WAXS, respectively) with contrast variation by using dry and wet (immersion in benzene and m-xylene) samples. For the original carbon aerogel, the surface area, S(SAXS), obtained by SAXS, is larger than that obtained by gas adsorption (S(ads)). The values become nearly the same as the degree of activation of the carbon aerogel increases. This feature is due to the widening of the narrow microporosity in the carbon aerogel as the degree of activation is increased. In addition, WAXS results show that the short-range spatial correlations into the assemblies of hydrocarbon molecules confined inside the micropores are different from those existing in the liquid phase.     

Mixed Co/Fe oxide nanoparticles in block copolymer micelles

Small iron oxide and Co-doped iron oxide nanoparticles (NPs) were synthesized in a commercial amphiphilic block copolymer, poly(ethylene oxide)-b-poly(methacrylic acid) (PEO 68-b-PMAA8), in aqueous solutions. The structure and composition of the micelles containing guest molecules (metal salts) or NPs (metal oxides) were studied using transmission electron microscopy, dynamic light scattering, X-ray photoelectron spectroscopy, and X-ray powder diffraction. The enlarged micelle cores after incorporation of metal salts are believed to be formed by both PMAA blocks containing metal species and penetrating PEO chains. The nanoparticle size distributions in PEO 68-b-PMAA8 were determined using small-angle X-ray scattering (SAXS) in bulk. Two independent methods for SAXS data interpretation for comprehensive analysis of volume distributions of metal oxide NPs showed presence of both small particles and larger entities containing metal species which are ascribed to organization of block copolymer micelles in bulk. The magnetometry measurements revealed that the NPs are superparamagnetic and their characteristics depend on the method of the NP synthesis. The important advantage of the PEO 68-b-PMAA8 stabilized magnetic nanoparticles described in this paper is their remarkable solubility and stability in water and buffers.     

Rapid internal bubble formation in a microwave heated polymer observed in real-time by X-ray scattering

A combined study of small-angle and wide-angle X-ray scattering (SAXS/WAXS) of the melting of a nylon-6 sample by localized microwave radiation has shown that this method can reveal the presence of bubbles forming and disappearing rapidly in real time in the interior of the sample due to its thermal decomposition.     

Solvent/gelator interactions and supramolecular structure of gel fibers in cyclic bis-urea/primary alcohol organogels

An organogel system consisting of trans-(1S,2S)-bis(ureidododecyl)cyclohexane (SS-BUC) and a series of primary alcohols was explored with optical polarizing microscopy (OPM), electron microscopy, circular dichroism (CD), wide-angle X-ray scattering (WAXS), and synchrotron small-angle X-ray scattering (SAXS). OPM, SAXS, and especially WAXS showed that the gel fiber of SS-BUC/methanol gels essentially consists of SS-BUC crystal itself. SAXS showed that the SS-BUC crystal in the gel takes a lamella with a domain spacing of 5.2 nm. When we left the gel at room temperature, the spacing decreased to 3.1 nm after several months. This distance change may correspond to the structural transition from a double-layer structure to an intercalated-layer structure, which was proposed by Feringa et al. (Chem.-Eur. J. 1999, 5, 937-950) as a possible arrangement of the molecular packing. When the gels in ethanol, propanol, butanol, or octanol were examined, they never showed crystalline peaks in WAXS and SAXS, indicating the amorphous nature of the gels. With increasing the alkyl chain length from ethanol to octanol, dramatic changes were observed in the CD spectrum in the 200-500-nm range. Because these CD changes are correlated to the absorbance of urea, those can be considered as the evidence that the solvents strongly relate to the spatial arrangement between the adjacent urea groups. For the amorphous gels, the cross-sectional correlation function [gammaCu] was directly obtained by the inverse Hankel transform of the SAXS data. The value of gammaCu for the gels is decreased with increasing u (distance between the two scattering bodies, see eq 5). Furthermore, it more rapidly decreases than that of the rigid cylinder model. This feature can be explained by the speculation that many solvent molecules permeate into the SS-BUC fiber. There was a clear difference between ethanol and the other gels, indicating that the solvents with a longer alkyl chain give the more permeated and diffused fiber. This permeated fiber (i.e., wet fiber) can rationalize the dramatic CD change, by presuming that the permeated solvent molecules alter the molecular stacking form.     

A physico-chemical characterisation of new raw materials for microcrystalline cellulose manufacturing

A detailed physico-chemical characterisation of potential new cellulose sources (rice husk, hemp stalk, and coniferous needles), and microcrystalline cellulose (MCC) manufactured from them, was made in this work. The length and the width of the cellulose crystallites were determined by wide-angle X-ray scattering (WAXS), crystallinities were studied by means of WAXS and solid state cross polarisation magic angle spinning ¹³C nuclear magnetic resonance (NMR) spectroscopy, and the packing and the cross-sectional shape of the microfibrils were determined by small-angle X-ray scattering. When MCC was prepared from rice husks and hemp stalks an acceptable yield was obtained. Crystallinities obtained with solid state NMR spectroscopy and WAXS were highest for MCC prepared from hemp stalks, and lowest for rice husk MCC. The crystallite sizes of MCC samples studied in this work varied more than in those MCC samples which were prepared from conventional plant sources, and crystallite size and cellulose crystallinity were related. When taking into account rather high values of specific surface, hemp stalks and rice husks appear as a promising raw materials for MCC production.