Rheology of carbon nanofiber-reinforced polypropylene

The rheological properties of two different nanocomposite systems consisting in the dispersion of carbon nanofibers (CNFs) in polypropylene are investigated. The nanoreinforced systems were identically prepared with two CNFs that differ only in the length of the fibers being otherwise identical to analyze the effect of fiber aspect ratio. Linear dynamic viscoelasticity and the steady-state rheology of the two different nanocomposites are presented. The system reinforced with CNFs with larger aspect ratio shows several rheological features that resemble peculiarities of rodlike polymers in the nematic liquid crystalline phase.     

Impact of glycosylation on physico–chemical and biological properties of nitrification inhibitors

The lipophilic 2-mercaptobenzothiazole (MBT), known for its nitrification inhibition properties, was derivatized thanks to direct glycosylation reactions. Similar transformations were also performed starting from 2-mercaptobenzimidazole (MBI), structurally close to MBT. The resulting S-linked mono- or disaccharides derived from d-glucose or l-arabinose, and cellobiose, gentiobiose or lactose, respectively, were subsequently studied as novel nitrification inhibitors without any further formulation or physical processes, except dilution in water. Along with ecotoxicity measurements, inhibition properties of the synthesized water soluble glycoconjugates were studied in a model reactor containing nitrification bacteria. The best results were obtained for the gentiobiosyl derivatives simply dissolved in water.     

Structural and vibrational characterization of medieval like glass samples

Within the framework of a project aimed to develop protective coatings for antique glass windows, three glass varieties of medieval-like composition were prepared using recipes deduced from archaeometric studies and different amounts of potassium for fluxing (15–20–25 K₂O wt.%). Batches were melted in mullite crucibles using an electric furnace at 1350 °C, the glass was fast cooled in air and annealed at temperatures 20 °C higher than the sample glass transition temperatures (726, 702 and 683 °C for V1, V2 and V3, respectively). The chemical composition of the glass was determined by X-Ray Fluorescence Spectroscopy (XRF) and the glass transition temperature was checked by differential thermal analysis (DTA). X-Ray Powder Diffraction (XRPD) data and vibrational spectroscopic experiments (FT-IR and Raman) revealed a direct dependence of glass de-polymerization on potassium content. In particular, the Raman data were interpreted on the basis of SiO₄ structural units Qⁿ and the polymerization index I_p.     

First measurement of the partial widths of 209Bi decay to the ground and to the first excited states

209Bi alpha decay to the ground and to the first excited state have been recently observed for the first time with a large BGO scintillating bolometer. The half-life of 209Bi is determined to be τ(1/2)=(2.01±0.08)×10(19) yr while the branching ratio for the ground-state to ground-state transition is (98.8±0.3)%.     

Low-temperature metal-induced crystallization of Mn-containing amorphous Ge thin films

This work focuses on the crystallization of amorphous germanium (a-Ge) thin films induced by manganese species. A series of Mn-containing a-Ge films ([Mn] ~ 0?3.7 at.% range) was deposited at 150 °C by the cosputtering technique. After deposition, all films were submitted to isochronal thermal annealing treatments up to 600 °C and analyzed by Raman scattering, optical transmission spectroscopy and electrical resistivity measurements. The experimental results indicate that: (a) Mn impurity lowers the crystallization temperature of a-Ge in ~ 100 °C, as confirmed by the Raman analyses, (b) the optical properties of the films are affected by both the insertion of Mn and the temperature of thermal treatment, with the optical bandgap staying in the range of ~ 0.7?1 eV, and (c) the electrical resistivity of the samples is also influenced by the Mn concentration and by the temperature of annealing, varying between ~ 1.0×10¹ and 1.6×10⁴ Ω cm. These experimental observations were systematically studied and the possible reasons associated to them are presented and discussed.     

Tsallis’ statistics in the variability of El Niño/Southern Oscillation during the Holocene epoch

Analysis of the Tsallis q-triplet for the variability of El Niño Southern Oscillation (ENSO) index during the Holocene epoch (last 11,000 years) is presented. Three periods are analyzed, 0-7000, 7000-9700, 9700-11,000 years before the present. During the first and the third periods, the q-index values have the expected usual relations between them (q_sens<1<q_stat<q_rel), and in the second one there is an inversion between q_stat and q_rel (q_stat>q_rel).     

Synthesis of hematite/silica/polymer composite colloids with a tunable morphology

Hematite/SiO₂/polystyrene colloidal particles were synthesized through emulsion polymerization, in the presence of seeds coated with 3-methacryloxypropyltrimethoxysilane (MPS). Scanning and transmission electron microscopy studies indicate that flying saucer-like particles can be prepared by taking advantage of the coalescence phenomenon which occurs between growing polymer nodules when the MPS surface density of the coupling agent is high. By decreasing this density, multipod-like and raspberry-like composite particles were obtained, depending on the concentration of monomer.     

Organic-Free Synthesis of Zeolite Y with High Si/Al Ratios: Combined Strategy of In Situ Hydroxyl Radical Assistance and Post-Synthesis Treatment

Zeolite Y, with a high SiO₂/Al₂O₃ ratio (SAR), plays an important role in fluidized catalytic cracking processes. However, in situ synthesis of zeolite Y with high SARs remains a challenge because of kinetic limitations. Here, zeolite Y with an SAR of 6.35 is synthesized by a hydroxyl radical assisted route. Density-functional theory (DFT) calculations suggest that hydroxyl radicals preferentially enhanced the formation of Si-O-Si bonds, thus leading to an increased SAR. To further increase the SAR, a dealumination process was carried out using citric acid, with a subsequent second-step hydrothermal crystallization, giving an SAR of up to 7.5 while maintaining good crystallinity and high product yield. The resultant zeolite Y shows good performance in cumene cracking. Introduced here is a new strategy for synthesizing high SAR zeolite Y, which is widely used in commercial applications.     

Photoexcitation of the methionine-iron bond in iron(III) cytochrome c: bimolecular reaction with NADH

When iron(III) cytochrome c aqueous solutions containing NADH are irradiated with polychromatic light (wavelength greater than 280 nm), iron(II) cytochrome c and NAD+ in the stoichiometric ratio 2/1 are observed to be the principal reaction products, independently of the presence of oxygen; in addition, a minor process due to direct photodegradation of the nucleotide is observed. The selection of monochromatic 290 nm irradiation light (at which NADH has an absorbance minimum) and an adequate reactant concentration allowed parallel reactions to be minimized and new information to be obtained on the mechanism of the photoredox process. The experimental results are consistent with a reaction mechanism whereby NADH donates one electron to a "reactive intermediate" of the hemoprotein formed from the light-induced methionine-to-iron charge transfer excited state. In this process an NAD. radical is formed which, in deaerated solution, immediately reduces another molecule of the hemoprotein, and is itself oxidized to NAD+. In aerated solution, the NAD. radical rapidly reacts with oxygen to give NAD+ and superoxide O2- anion radical which, in turn, reduces the second iron(III) cytochrome c molecule.     

Role of guiding groups in cinchona-modified platinum for controlling the sense of enantiodifferentiation in the hydrogenation of ketones

Systematic structural variations of cinchona-type modifiers used in the platinum-catalyzed hydrogenation of ketones give insight into the adsorption mode of the modifier and its interaction with the substrate on the platinum surface under truly in situ conditions. The performance of a new modifier, O-(2-pyridyl)-cinchonidine, is compared to that of O-phenyl-cinchonidine and cinchonidine (CD). In the hydrogenation of ethyl pyruvate, ketopantolactone, and 2-methoxyacetophenone, CD gives the (R)-alcohol in excess. Introduction of the bulky O-phenyl group favors the (S)-enantiomer, whereas upon replacement of the phenyl by a 2-pyridyl group the (R)-alcohol is again the major product. This finding is particularly striking, because the two ether groups have virtually identical van der Waals volumes. A catalytic study including the nonlinear behavior of modifier mixtures, and attenuated total reflection infrared spectroscopy of the solid-liquid interface in the presence of hydrogen, revealed the adsorption mode and strength of the modifiers on Pt. Theoretical calculations of the modifier-substrate interactions offered a feasible explanation for the different role of the bulky ether groups: repulsion by the phenoxy and attraction by the 2-pyridoxy groups. Simulation of the interaction of o-pyridoxy-CD with ketopantolactone on a model Pt surface suggests that formation of two N-H-O-type H-bonds--involving the quinuclidine and pyridine N atoms, and the two keto-carbonyls in the substrate--controls the adsorption of the substrate during hydrogen uptake. This mechanistic study demonstrates the potential of insertion of suitable substituents into CD and their influence on adsorption and stereocontrol on the platinum surface.