Nuclear resonant scattering of synchrotron radiation by multilayer structures

Multilayer structures form a particular class of samples employed in nuclear resonant scattering of synchrotron radiation. Their specific properties lead to unusual energy and time characteristics of nuclear resonant scattering, which differ much from those of single crystals. The analysis of these distinctions is presented. Several approaches to achieve pure nuclear reflections with multilayers are discussed. Finally, we review the studies of multilayer structures with nuclear resonant scattering of synchrotron radiation.

     

Possibility of hgh Z material detection by a setup for natural cosmic-ray muon flux measurement

A design is proposed and a resolving power is calculated for a detector that monitors the unauthorized transportation of high Z materials (nuclear materials with Z > 90) using the natural cosmic-ray muon flux. The identification of nuclear materials is based on the strong dependence of the multiple scattering angle on the matter charge upon traversing the matter by cosmic muons. It is proposed that chambers assembled from drift aluminum tubes similar to chambers used in the muon system of the ATLAS detector be used as the coordinate detector for the setup. The calculations show that the proposed variant of the setup makes it possible to detect the presence of nuclear materials with a weight of about 0.5–1 kg and higher in the inspected volume in a measurement time of several minutes.     

The bond force constants and elastic properties of boron nitride nanosheets and nanoribbons using a hierarchical modeling approach

A hierarchical approach bridging the atomistic and nanometric scales is used to compute the elastic properties of boron nitride nanosheets and nanoribbons, examining the effect of sheet size, aspect ratio and anisotropy. The approach consists in obtaining the bond force (force field) constants by dedicated computations based on density functional theory (DFT) and using such constants as input for larger scale structural models solved by finite element analysis (FEA). The bond force constants calculated by DFT are 616.9 N/m for stretching, 6.27×10⁻¹⁹ Nm/rad² for in-plane rotation and 1.32×10⁻¹⁹ Nm/rad² for dihedral rotation. Using these constants, the elastic properties of boron nitride nanosheets and nanoribbons predicted by FEA are almost independent of the sheet size, but strongly dependent on their aspect ratio. The sheet anisotropy increases with increased aspect ratio, with nanoribbons of aspect ratios of 10 exhibiting a ratio of elastic moduli along both in-plane directions of 1.7.     

The phase behavior of a polymer‐fullerene bulk heterojunction system that contains bimolecular crystals

Polymer:fullerene blends have been widely studied as an inexpensive alternative to traditional silicon solar cells. Some polymer:fullerene blends, such as blends of poly(2,5‐bis(3‐tetradecylthiophen‐2‐yl)thieno[3,2‐b]thiophene (pBTTT) with phenyl‐c71‐butyric acid methyl ester (PC₇₁BM), form bimolecular crystals due to fullerene intercalation between the polymer side chains. Here we present the determination of the eutectic pBTTT:PC₇₁BM phase diagram using differential scanning calorimetry (DSC) and two‐dimensional grazing incidence X‐ray scattering (2D GIXS) with in‐situ thermal annealing. The phase diagram explains why the most efficient pBTTT:PC₇₁BM solar cells have 75–80 wt % PC₇₁BM since these blends lie in the center of the only room‐temperature phase region containing both electron‐conducting (PC₇₁BM) and hole‐conducting (bimolecular crystal) phases. We show that intercalation can be suppressed in 50:50 pBTTT:PC₇₁BM blends by using rapid thermal annealing to heat the blends above the eutectic temperature, which forces PC₇₁BM out of the bimolecular crystal, followed by quick cooling to kinetically trap the pure PC₇₁BM phase. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

A computational investigation on the geometries,stabilities, antioxidant activity,and the substituent effects of the L‐ascorbic acid and their derivatives

The geometries, stabilities, and antioxidant activities of L‐Ascorbic acid (1a), D‐erythroascorbate (2a), and D‐erythroascorbate glucoside (3a) as well as their sulfur and selenium derivatives are systematically investigated by using density functional theory. Emphasis is placed on studies of the two main mechanisms, that is, hydrogen atom donation and single‐electron transfer, and the O—H bond dissociation enthalpy and the ionization potential are computed in the gas phase and water solution. The calculated results indicate that the 2‐OH group in the five‐membered ring acts as an important H atom donor to free radicals. The 2‐OH radical spin density distribution shows that the unpaired electron is mostly located at the C3 atom of the five‐membered ring and partially at the vicinal O atoms, proving that a certain delocalization of the odd electron is effective in the five‐membered ring. In water aqueous solution, the antioxidant capacity and the electron donating ability are increased as the O atom in the five‐membered ring of 1a, 2a, and 3a is replaced by S and Se, respectively, in good agreement with experimental measurements; Furthermore, their antioxidant capacities are enhanced as compared with the standard antioxidant (resveratrol). © 2013 Wiley Periodicals, Inc.     

Investigating Membrane-Mediated Antimicrobial Peptide Interactions with Synchrotron Radiation Far-Infrared Spectroscopy

Synchrotron radiation-based Fourier transform infrared spectroscopy enables access to vibrational information from mid over far infrared to even terahertz domains. This information may prove critical for the elucidation of fundamental bio-molecular phenomena including folding-mediated innate host defence mechanisms. Antimicrobial peptides (AMPs) represent one of such phenomena. These are major effector molecules of the innate immune system, which favour attack on microbial membranes. AMPs recognise and bind to the membranes whereupon they assemble into pores or channels destabilising the membranes leading to cell death. However, specific molecular interactions responsible for antimicrobial activities have yet to be fully understood. Herein we probe such interactions by assessing molecular specific variations in the near-THz 400–40 cm⁻¹ range for defined helical AMP templates in reconstituted phospholipid membranes. In particular, we show that a temperature-dependent spectroscopic analysis, supported by 2D correlative tools, provides direct evidence for the membrane-induced and folding-mediated activity of AMPs. The far-FTIR study offers a direct and information-rich probe of membrane-related antimicrobial interactions.     

Effect of selected dopants on conductivity and moisture stability of Li3PS4 sulfide solid electrolyte: a first-principles study

The first principle computational screening was performed to investigate the effect of selected dopants for Li₃PS₄ sulfide solid electrolyte on its ionic conductivity and stability toward moisture. The results suggest that substitution P⁵⁺ using isovalent cations whose electronegativity (EN) value is closer to the value of S has more significant effects on the ionic conductivity, whereby W⁵⁺ and Sb⁵⁺ can improve most. Similarly, aliovalent cation substitutions with compensating changes in the lithium-ion concentration, particularly those with a lower oxidation state and higher EN, such as Cu²⁺, effectively enhance the lithium-ion conductivity in this structure. For cation dopants, it is found that ionic conductivity improvement of Li₃PS₄ is the synergetic effect of EN and oxidation number of the dopant as well as the material's lattice parameter change. Oxides of the considered cation dopants can also improve the ionic conductivity of the material but have much lower lithium-ion conductivity than the cases of cation dopants. However, the metal oxide dopants, particularly those derived from soft Lewis' acid cations, show a marginal improvement in moisture stability of the Li₃PS₄ electrolyte. The effect of halides and metal halide dopants on the lithium-ion conductivity and moisture stability of Li₃PS₄ electrolyte are also studied. It is found that metal halides are more effective than any other dopants in improving the ionic conductivity of Li₃PS₄.     

Heterostructured composite of NiFe-LDH nanosheets with Ti4O7 for oxygen evolution reaction

Developing oxygen evolution reaction (OER) electrocatalyst based on earth-abundant materials holds great promise for ascertaining water-splitting to surmount its deprived kinetics. In this regard, NiFe-LDH (layered double hydroxide) receives considerable attention owing to their layered structure. However, they still suffer from poor electronic conductivity and structural stability. We combined NiFe-LDH nanosheets with Magnéli phase Ti₄O₇ into a heterostructured composite. A series of analyses reveal that decorating Ti₄O₇ facilitates charge transfer to enhance the conductivity of NiFe-LDH-Ti₄O₇. During electrochemical measurement, Ni²⁺ is transformed to metastable Ni³⁺ (Ni (OH)→ NiOOH) before the OER onset potential. Thus, the presence of Ni³⁺ as the main active sites could improve the chemisorption of OH^? to facilitate OER. As a result, the NiFe-LDH-Ti₄O₇ catalyst delivers as low as onset potential (1.43 V). Combining the holey structure (NiFe-LDH and Ti₄O₇) and the defect engineering generated on NiFe-LDH-Ti₄O₇ as a synergistic effect improves the OER performance. The inclusion of Ti₄O₇ in the composite leads to more vacancy sites, as evidenced by the extended X-ray absorption fine structure (EXAFS) analysis. The obtained defective structure with a low coordination environment would improve the electronic conductivity and facilitate the adsorption process of H₂O onto metal cations, thereby increasing the intrinsic catalytic activity of NiOOH. The strong coupling of NiFe-LDH and Ti₄O₇ also increases the stability, and the heterostructured composite helps maintain the structural robustness of the LDH.     

A universal blown film apparatus for <Emphasis Type="Italic">in situ</Emphasis> X-ray measurements

A setup of blown film machine combined with in situ synchrotron radiation X-ray diffraction measurements and infrared temperature testing is reported to study the structure evolution of polymers during film blowing. Two homemade auto-lifters are constructed and placed under the blown machine at each end of the beamline platform which move up and down with a speed of 0.05 mm/s bearing the 200 kg weight machine. Therefore, structure development and temperature changes as a function of position on the film bubble can be obtained. The blown film machine is customized to be conveniently installed with precise servo motors and can adjust the processing parameters in a wide range. Meanwhile, the air ring has been redesigned in order to track the structure information of the film bubble immediately after the melt being extruded out from the die exit. Polyethylene (PE) is selected as a model system to verify the feasibility of the apparatus and the in situ experimental techniques. Combining structure information provided by the WAXD and SAXS and the actual temperature obtained from the infrared probe, a full roadmap of structure development during film blowing is constructed and it is helpful to explore the molecular mechanism of structure evolution behind the film blowing processing, which is expected to lead to a better understanding of the physics in polymer processing.     

Improving the softness of BOPP films: From laboratory investigation to industrial processing

Young's modulus of biaxially oriented polypropylene (BOPP) films prepared with homemade film stretcher was investigated,which can be used to indicate the softness of fihns.It was found that the modulus of films was decreased by about 69％ as the content of polyethylene (PE) added into polypropylene (PP) reached 30％.Also,increasing draw temperature can induce lower stress level during stretching,which may lead to the formation of crystals with low orientation level and thus decreased modulus of films.Based on laboratory study,BOPP films produced on commercial line were studied by differential scanning calorimetry (DSC),wide and small-angle X-ray scattering (WAXS,SAXS) with varying contents of PE.SAXS results show that the crystals are oriented in both machine direction (MD) and transverse direction (TD),and the crystals are more oriented in TD than MD according to the WAXS results for all films.Also,the orientation parameter of crystal along TD increases from 0.68 to 0.83 as the contents of PE increase from 0％ to 25％.Meanwhile,the modulus of films in MD declines with increase of PE contents generally,improving the film softness.Orientation of crystals is thus an effective structure parameter to adjust the film softness.The relationship of processing-structure-property is also established.