Wide Angle X-ray Spectroscopy Research Articles

High-efficiency organic photovoltaic cells processed using a non-halogen solvent

In this paper we describe high-performance PM6:BTP-eC9–based organic photovoltaic (OPV) cells prepared using non-halogen solvents, with the goal of minimizing any potential environmental pollution. We investigated three green solvents (toluene, o-xylene, and 1,2,4-trimethylbenzene) as replacements for the commonly used chloroform. Using UV–Vis spectroscopy, atomic force microscopy, two-dimensional grazing incidence wide-angle X-ray spectroscopy, and carrier transport analysis, we optimized the blend films and investigated their optoelectronic properties and those of their respective devices. Among our tested devices, the OPV cell prepared with toluene as the solvent and 1,8-diiodooctane (DIO) as the additive displayed the best performance, with a power conversion efficiency (15.8 ± 0.20%) comparable with that of the chloroform-derived OPV (16.2 ± 0.1%). Thus, it is feasible to replace halogen solvents with non-halogen solvents when preparing OPV devices.

On the electrocatalytical oxygen reduction reaction activity and stability of quaternary RhMo-doped PtNi/C octahedral nanocrystals.

Recently proposed bimetallic octahedral Pt–Ni electrocatalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cell (PEMFC) cathodes suffer from particle instabilities in the form of Ni corrosion and shape degradation. Advanced trimetallic Pt-based electrocatalysts have contributed to their catalytic performance and stability. In this work, we propose and analyse a novel quaternary octahedral (oh-)Pt nanoalloy concept with two distinct metals serving as stabilizing surface dopants. An efficient solvothermal one-pot strategy was developed for the preparation of shape-controlled oh-PtNi catalysts doped with Rh and Mo in its surface. The as-prepared quaternary octahedral PtNi(RhMo) catalysts showed exceptionally high ORR performance accompanied by improved activity and shape integrity after stability tests compared to previously reported bi- and tri-metallic systems. Synthesis, performance characteristics and degradation behaviour are investigated targeting deeper understanding for catalyst system improvement strategies. A number of different operando and on-line analysis techniques were employed to monitor the structural and elemental evolution, including identical location scanning transmission electron microscopy and energy dispersive X-ray analysis (IL-STEM-EDX), operando wide angle X-ray spectroscopy (WAXS), and on-line scanning flow cell inductively coupled plasma mass spectrometry (SFC-ICP-MS). Our studies show that doping PtNi octahedral catalysts with small amounts of Rh and Mo suppresses detrimental Pt diffusion and thus offers an attractive new family of shaped Pt alloy catalysts for deployment in PEMFC cathode layers.

Investigation of the useability of polyester protective cover for PVDF-based polymer gel electrolytes

Abstract Different techniques were used to investigate the possibility of using polyester thin film as a heat-protective cover for polyvinylidene fluoride (PVDF)-gel samples, in an attempt to stop or reduce solvent loss during thermal analyses. Two experimental techniques were used for this goal; namely hot polarized optical microscopy and hot wide-angle x-ray spectroscopy (WAXs). The measurements were taken using various configurations and conditions in the experimental techniques to check the usability of the polyester as a container-protective cover when the PGE samples undergo high heating loads. The results showed a significant effect on PVDF-gel electrolytes transparency, but no morphology changes were detected. This a good indication that encourages using this type of protective film in different applications such as Li-ion batteries.

Surface properties of buffer layers affect the performance of PM6:Y6–based organic photovoltaics

In this study we used p-type [poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) and nickel oxide] and n-type (sol–gel and nanoparticle zinc oxides) materials as transporting layers for PM6:Y6–based organic photovoltaic (OPV) devices. These solution-processed transporting layers exhibited various surface energies, morphologies, and roughnesses that affected the subsequent growth of PM6:Y6 blend films. Using atomic force microscopy and grazing-incidence wide-angle X-ray spectroscopy, we observed various PM6:Y6 blend film morphologies on the different substrates. Furthermore, the surface-induced PM6:Y6 blend morphology influenced the mechanism of carrier recombination and, thereby, affected the device performance. Among our tested systems, the PEDOT:PSS–based devices exhibited superior surface properties, possessed larger phase-segregated domains, and featured strong molecular packing, all of which resulted in OPVs displaying power conversion efficiencies (PCEs) of up to 11.5%. When incorporating 1-chloronaphthalene as an additive during solution processing, the molecular packing was enhanced, thereby improving the PCE of the resulting devices from 11.5 to 13.4%. Devices incorporating ZnO (sol–gel) displayed performance comparable with that of the PEDOT:PSS–based devices, but exhibited superior air stability without encapsulation (25 °C, 40% humidity). • We have evaluated PM6:Y6 OPV devices featuring various transporting layers. • The champion OPV device displayed a PCE of 13.4 ± 0.23%. • The unencapsulated ZnO devices possessed good air-stability, retaining 90% of their PCEs after storage in air for over 190 h.

Noninvasive high-frequency acoustic microscopy for 3D visualization of microstructure and estimation of elastic properties during hydrolytic degradation of lactide and ε-caprolactone polymers

The monitoring of degradation processes' kinetics in polymers is one of the attractive possibilities of ultrasound technique applications that provide non-destructive imaging of polymers' internal microstructure and measurements of elastic properties. In this work, biodegradable polymers and copolymers based on L,L-lactide, D,L-lactide and ε-caprolactone have been studied at different stages of hydrolysis at 37 °C by high-frequency (100 and 200 MHz) ultrasound. The acoustic microscopy technique has been developed to reveal changes in the internal microstructure and bulk sound speed in polymer samples over a hydrolysis period of 25 weeks. Ultrasound imaging provides visualization of amorphous and crystalline phases, internal imperfections, variation in packing density, and other microstructural features. Acoustic images demonstrate nucleation, growth, and the changes in internal inhomogeneities in polymers during degradation accompanied by a decrease in the polymers' molecular weight. We associate the changes in the elastic properties (the speed of a longitudinal wave) with crystallinity variations in polymers during hydrothermal aging. The results of the ultrasound investigations are supplemented by gel permeation chromatography, differential scanning calorimetry, and wide-angle X-ray spectroscopy. Statement of SignificanceMonitoring the kinetics of degradation processes in polymers is one of the attractive possibilities of applying ultrasound techniques that provide non-destructive imaging of the polymers' internal microstructure and measurements of elastic properties. In this work, visualization of nucleation, growth, and evolution of internal inhomogeneities in the volume of polymers and variation of values of speed of longitudinal and transverse sound waves during hydrolysis are compared with measurements of molecular weight, density, data of DSC curves, and X-ray scattering analysis. We discuss several common phenomena that occur in the volume of poly(L-lactide) and poly(D,L-lactide) over the degradation process as well as improvement of elastic properties of the poly(ε -caprolactone) and poly(L-lactide-co-caprolactone) during hydrothermal aging.

Efficient near-infrared light-emitting diodes based on quantum dots in layered perovskite

Light-emitting diodes (LEDs) based on excitonic material systems, in which tightly bound photoexcited electron–hole pairs migrate together rather than as individual charge carriers, offer an attractive route to developing solution-processed, high-performance light emitters. Here, we demonstrate bright, efficient, excitonic infrared LEDs through the incorporation of quantum dots (QDs)1 into a low-dimensional perovskite matrix. We program the surface of the QDs to trigger fast perovskite nucleation to achieve homogeneous incorporation of QDs into the matrix without detrimental QD aggregation, as verified by in situ grazing incidence wide-angle X-ray spectroscopy. We tailor the distribution of the perovskites to drive balanced ultrafast excitonic energy transfer to the QDs. The resulting LEDs operate in the short-wavelength infrared region, an important regime for imaging and sensing applications, and exhibit a high external quantum efficiency of 8.1% at 980 nm at a radiance of up to 7.4 W Sr−1 m−2. Embedding perovskite quantum dots in perovskite leads to bright, efficient 980 nm LEDs with applications in imaging and sensing.

Controlling Near-Surface Ni Composition in Octahedral PtNi(Mo) Nanoparticles by Mo Doping for a Highly Active Oxygen Reduction Reaction Catalyst.

We report and study the translation of exceptionally high catalytic oxygen electroreduction activities of molybdenum-doped octahedrally shaped PtNi(Mo) nanoparticles from conventional thin-film rotating disk electrode screenings (3.43 ± 0.35 A mgPt-1 at 0.9 VRHE) to membrane electrode assembly (MEA)-based single fuel cell tests with sustained Pt mass activities of 0.45 A mgPt-1 at 0.9 Vcell, one of the highest ever reported performances for advanced shaped Pt alloys in real devices. Scanning transmission electron microscopy with energy dispersive X-ray analysis (STEM-EDX) reveals that Mo preferentially occupies the Pt-rich edges and vertices of the element-anisotropic octahedral PtNi particles. Furthermore, by combining in situ wide-angle X-ray spectroscopy, X-ray fluorescence, and STEM-EDX elemental mapping with electrochemical measurements, we finally succeeded to realize high Ni retention in activated PtNiMo nanoparticles even after prolonged potential-cycling stability tests. Stability losses at the anodic potential limits were mainly attributed to the loss of the octahedral particle shape. Extending the anodic potential limits of the tests to the Pt oxidation region induced detectable Ni losses and structural changes. Our study shows on an atomic level how Mo adatoms on the surface impact the Ni surface composition, which, in turn, gives rise to the exceptionally high experimental catalytic ORR reactivity and calls for strategies on how to preserve this particular surface composition to arrive at performance stabilities comparable with state-of-the-art spherical dealloyed Pt core-shell catalysts.

Microstructures of cellulose coagulated in water and alcohols from 1-ethyl-3-methylimidazolium acetate: contrasting coagulation mechanisms

Coagulation of cellulose solutions is a process whereby many useful materials with variable microstructures and properties can be produced. This study investigates the complexity of the phase separation that generates the structural heterogeneity of such materials. The ionic liquid, 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]), and a co-solvent, dimethylsulfoxide (DMSO), are used to dissolve microcrystalline cellulose in concentrations from 5 to 25 wt%. The solutions are coagulated in water or 2-propanol (2PrOH). The coagulated material is then washed and solvent exchanged (water → 2PrOH → butanone → cyclohexane) in order to preserve the generated microstructures upon subsequent drying before analysis. Sweep electron microscopy images of 50 k magnification reveal open-pore fibrillar structures. The crystalline constituents of those fibrils are estimated using wide-angle X-ray spectroscopy and specific surface area data. It is found that the crystalline order or crystallite size is reduced by an increase in cellulose concentration, by the use of the co-solvent DMSO, or by the use of 2PrOH instead of water as the coagulant. Because previous theories cannot explain these trends, an alternative explanation is presented here focused on solid–liquid versus liquid–liquid phase separations.Graphical abstract

Comparative Study of Xylan Extracted by Sodium and Potassium Hydroxides (NaOH and KOH) from Bagasse Pulp: Characterization and Morphological Properties

Xylan is the second most abundant polysaccharide and the predominant hemicellulose component of soda bagasse pulp. The present endeavor focuses on increasing the value addition to underutilized agro-industrial residue such as bagasse. For this purpose, xylan was isolated by two conventional alkali extraction methods i.e. NaOH and KOH. The recovery rate and sugar composition of different reaction times and alkali consumptions were monitored with advanced method such as High Performance Liquid Chromatography (HPLC). The Fourier Transform Infrared Spectroscopy (FTIR) and Wide Angle X-ray spectroscopy (WAXS) were respectively employed to characterize the functional groups and Crystallinity Index (CrI) changes during the extraction process. It was explored that highest xylan recovery rates were obtained with 6% of NaOH at 120 min and 6% KOH at 45 min. The xylan morphology via WAXS was found that its structure to be amorphous. HPLC results also showed KOH had higher effectiveness than NaOH in terms of extracted xylan purity. Highest XGRs (Xylose to Glucose Ratios) were also achieved by KOH processes. Hence, this study contributes to the adequate utilization of agricultural residues, with promising potential for applications in the production of certain novel materials and chemical conversion industries.

Spontaneous formation of polylactide stereocomplex microspheres containing metal ions

Linear poly(l-lactides) (PLLAs) and poly(d-lactides) (PDLAs) with Mn in the range 2000 − 4300 containing a different number and placement of carboxyl groups were obtained via cationic ring-opening polymerization and post-polymerization functionalization. PLA stereoisomers (PLLA-(COOH)x and PDLA-(COOH)x, where x = 1 − 3) were used for the investigation of stereocomplexation in solution performed in the presence of metal cations such as Ca2+, Mg2+, Zn2+, Fe3+. Spherical microparticles with a diameter in the range 0.7 − 3.0 µm were obtained in all cases which was confirmed on the basis of scanning electron microscopy (SEM) analysis. The microsphere size and homogeneity were analyzed depending on the stereocomplexation conditions and the molecular weight as well as the number of carboxyl end groups in the PLLA and PDLA used for stereocomplexation. The PLA microspheres obtained were analyzed by Fourier transform IR spectroscopy, wide angle X-ray spectroscopy and energy-dispersive X-ray spectroscopy methods which confirmed the presence of metal cations inside. The application of regular microspheres with metal ions as drug delivery systems is considered. © 2016 Society of Chemical Industry

Direct synthesis of fibrous high molecular weight polyethylene using vanadium catalysts supported on an SiO2ionic liquid system

Polyethylene of fibrous morphology was obtained using Cp2VCl2 and VCl2(salenCl2) catalysts activated by AlEt2Cl and AlEtCl2 and heterogenized on a supported ionic liquid system prepared with SiO2 and 1-(3-triethoxysilyl)propyl-3-methylimidazolium chloroaluminate. The fibre length ranges from 15 to 60 µm, depending on the reaction conditions. The polyethylene is characterized by a high molecular weight ((1.1–2.4) × 106 g mol−1) and a narrow molecular weight distribution (1.4–2.5). It is a linear polymer, properly without branching. The DSC method reveals characteristic changes in melting temperature and crystallinity degree between the first and second scan heating cycles (141 °C and 136 °C, 71% and 46%, respectively). The wide angle X-ray spectroscopy and Fourier transform infrared spectroscopy methods give crystallinity degree values of 40% and 41%–51%. The influence of type of catalyst precursor, alkylaluminium activator, catalyst/activator molar ratio, reaction time and temperature is discussed. © 2015 Society of Chemical Industry

Influence of parameters of molecular mobility on formation of structure in ferroelectric vinylidene fluoride copolymers

The low-temperature molecular mobility has been studied by dielectric relaxation spectroscopy on the bulk films of statistic copolymers of vinylidene fluoride (VDF) with tetra- (TFE) and trifluoroethylene obtained by crystallization from a solution in acetone. The results show that activation energy of the kinetic units in the glassy state depends significantly on the concentration of polar groups. The cooperative mobility above the glass transition temperature is described by Vogel-Tamman-Fulcher equation; the lowest value of the effective activation energy was found in the copolymer with highest amount of non-polar TFE content. It has been shown that the parameters of the dynamics are related to the structural parameters obtained by infrared spectroscopy, wide-angle X-ray Spectroscopy, and small-angle X-ray scattering. In particular, the largest crystals and the highest value of the “large” period have been detected in VDF/TFE copolymer with lowest activation parameters of microbrownian and local mobility. Number of lamellar crystals in stacks is determined by the concentration of VDF polar groups in copolymer chain.

Synthesis and characterization of selective thiourea modified Hg(II) ion-imprinted cellulosic cotton fibers

In the present study, Hg2+ ion-imprinted chelating fibers based on thiourea modified natural cellulosic cotton fibers (Hg-C-TU) were synthesized and characterized using some instrumental techniques such as elemental analysis, scanning electron microscopy (SEM), FTIR, wide angle X-ray and XPS spectroscopy. The modified Hg-C-TU fibers were employed for selective removal of Hg2+ from aqueous solution. Effect of some essential parameters such as pH, temperature, adsorption times and adsorbate concentration were examined to evaluate the optimum adsorption condition. The adsorption kinetics followed the second-order kinetic model indicating that the chemical adsorption is the rate limiting step. Also, the adsorption isotherm experiments showed the best fit with Langmuir model with maximum adsorption capacities 110.3 and 61.8mg/g for both Hg-C-TU and NI-C-TU, respectively.

Moisture induced plasticity of amorphous cellulose films from ionic liquid

Amorphous cellulose films were created by regeneration from 1-Ethyl-3-methylimidazolium acetate (EmimAc) solutions. Their mechanical properties were analyzed as a function of water content. Cellulose with different molecular weights, i.e. microcrystalline cellulose (Avicel), Spruce cellulose and bacterial nanocellulose (BNC), were used for film preparation. All the regenerated films were free from EmimAc residues as shown by Fourier transform infrared spectroscopy (FTIR), amorphous as shown by wide angle X-ray spectroscopy (WAXS) and optical transparent. The equilibrium water content (w/w) was measured at different relative humidities. The plasticizing effect of water on the films was evidenced by both tensile tests and dynamical mechanical analysis (DMA) with humidity scans. The mechanical properties were clearly related to the proportional water uptake of the films. The sample with the longest cellulose chains, i.e. BNC, showed significantly larger elongation to brake at high moisture content which was owed to chain entanglements.

Polyoctenamer - Single Walled Carbon Nanotube Composites: Spectroscopic Investigations

AbstractComposites of single walled carbon nanotube dispersed within polymeric matrices have been investigated by spectroscopic techniques (Raman and Wide Angle X-Ray Spectroscopy). Raman investigations included an in depth analysis of the radial breathing mode (for single wall carbon nanotubes) and a brief analysis of the lines originating from the polymeric matrix. Raman spectra were successfully simulated by computer assuming that the as recorded spectrum is a convolution of lines whose line shape is well described by a modified Breit-Wigner-Fano equation. The dependence of the position of the lines belonging to the radial breathing mode on the concentration of single walled carbon nanotube has been investigated, with emphasis on information pertinent to the stress transfer from the macromolecular matrix to the filler and to the coating of single walled carbon nanotube by polymeric chains. Complementary Wide Angle X-Ray Spectroscopy measurements provided information about the effect of the loading with single walled carbon nanotube on the crystal structure of the polymeric matrix. The research aims to a better understanding of the interactions between polymeric matrices and nanofillers.

Changes in the mechanical properties of compression moulded samples of poly(3-hydroxybutyrate- co-3-hydroxyvalerate) degraded by Streptomyces omiyaensis SSM 5670

Streptomyces omiyaensis SSM 5670 was characterized by its ability to use compression moulded samples of poly(3-hydroxybutyrate- co-3-hydroxyvalerate) (PHBV) as its sole carbon source. Biodegradation of PHBV in liquid mineral salts medium was investigated using scanning electron microscopy, gravimetric measurements, capillary viscometry, tensile testing and wide angle X-ray spectroscopy. The biodegradation of PHBV proceeds via surface erosion mechanism, resulting in the formation of pits by microbial attack. PHBV specimens lost about 45% of their original weight after 45 days of exposure. During the degradation process the elastic modulus reduces less than 10%. The formation of pores and microcracks initiated at the degraded pits determines the reduction of the elongation and stress at break. However, the true stress at break is practically independent of the degradation time. No significant changes of PHBV molecular weight or crystallinity were observed during biodegradation. The polymer chain cleavage occurred only at the specimen surface and does not discriminate between crystalline and amorphous states.

Microstructure and free volume evaluation of poly(vinyl alcohol) nanocomposite hydrogels

A new type of organic/inorganic nanocomposite hydrogel was prepared by introducing small amount of natural montmorillonite (MOM) into a poly(vinyl alcohol) (PVA)/sulfonated polyester (PES) system. The crystalline structure and crystallinity degree were determined by differential scanning calorimetry (DSC) and wide angle X-ray spectroscopy (WAXS). The presence of PES leads to an increase in the crystallinity degree of the PVA matrix and a significant decrease in the melting temperature. The addition of small amount of clay (1–5%) resulted in an increase of the average crystallite dimension, crystallinity degree and melting temperature, as compared to the PVA/PES system. The presence of the clay resulted in a substantial increase on the free volume size, as suggesting by positron annihilation lifetime spectroscopy (PALS). This result suggests a lower packing efficiency of the PVA chain and the formation of a PVA–MOM interfacial layer. This interfacial layer and the increasing of the mobility of the PVA chain by the presence of the clay reflects also in a decrease of the glass transition temperature, determined by dynamic mechanical analysis.

Structural and thermal interpretation of the synergy and interactions between the fire retardants magnesium hydroxide and zinc borate

The mechanism of cooperative action of commercial fire retardants is interpreted as resulting from specific chemical reaction and phase changes. This investigation focuses on the thermally initiated interactions between two forms of commercially available fire retardant compounds. The fire performance of a polyolefin with a metal hydroxide fire retardant, magnesium hydroxide, can significantly reduce the heat release rate through absorption of heat during conversion to its metal oxide. Formation of water, followed by vaporisation, decreases heat and dilutes volatiles from polymer degradation. The second form of fire retardant compounds are zinc borates (2ZnO·3B 2O 3·3H 2O and 4ZnO·B 2O 3·H 2O), that undergo dehydration with increasing temperature. Differential thermal analysis and wide-angle X-ray spectroscopy indicated that various structural changes occurred during heating. Endothermic transitions were observed for all components, while zinc borate (2ZnO·3B 2O 3·3H 2O) showed an exothermic crystallisation transition at relatively high temperature. The exotherm was modified by the development of a new crystalline phase, magnesium orthoborate (3MgO·B 2O 3) that formed on reaction with magnesium oxide (MgO) at temperatures greater than 500 °C. Formation of crystalline zinc oxide (ZnO) was also detected. From zinc borate (4ZnO·B 2O 3·H 2O), ZnO was primarily formed. No new crystalline phases were observed in the presence of MgO over the temperature range investigated.

Interfacial adhesion between semi-crystalline polymers (polypropylene and nylon-6): in situ compatibilized interface and fracture mechanism

The interfacial fracture toughness between semi-crystalline polymers (polyamide/polypropylene) were studied to understand the failure mechanisms at the interface, especially when the interface was reinforced by an in situ compatibilizer. Based on the observation of the interface using scanning electron microscopy and wide angle X-ray spectroscopy, it was revealed that crystalline structure of polypropylene was not affected by the in situ compatibilizer at the interface. The reinforcing mechanism could be qualitatively identified by investigating the evolution of fracture toughness as a function of annealing time and temperature. The adhesion strength increased with the annealing time. Depending on the annealing temperature, the fracture toughness passed a peak value and then reached a plateau after some bonding time. As long as the chain length of the compatibilizer is long enough to form entanglements with the molecules at both bulk sides, the fracture at the interface is decided by the balance between adhesion strength at the interface and cohesive strength in the weak modulus side; the failure locus follows the lower one. Thus, adhesive failure occurred first when the reaction at the interface did not occur long enough to provide high adhesive strength at the interface, but the cohesive failure occurred in the crack propagation side after the adhesive strength value became higher than the cohesive strength value.

The CO-adsorbate electrooxidation on ruthenium cluster-like materials

The electrochemical response and electrode potential-dependent infrared spectra for CO-adsorbate oxidation on unsupported ruthenium cluster-like material (Rux), prepared in two organic solvents: (xylene (Xyl), and 1,2-dichlorobenzene (Dcb)) from tris–ruthenium dodecacarbonyl decomposition, are reported. In spite of a similar particle size (2 nm) of the materials, the interfacial pseudo-capacitance of Rux(Xyl) is ca. four times higher than that of Rux(Dcb). Wide angle X-ray spectroscopy (WAXS) analysis on Rux(Xyl) and Rux(Dcb) nanoparticles revealed a high degree of structural disorder on Rux(Xyl) (J. Phys. Chem. B 105 (2001) 5238). The surface state of Rux(Xyl) and Rux(Dcb) used to oxidize CO, to form oxide-like (RuxOy) species, and used to recover the metallic nanoprecursor (under hydrogen annealing) can be inherently attributed to the degree of surface atom disorder. The CO absorption bands recorded on both types of surfaces are linear in nature and have apparently similar behavior to that observed on massive or well-defined ruthenium electrode surfaces.