Rheological Characterization of Alumina Ceramic Suspensions in Presence of a Dispersant and a Binder

The rheological responses of aqueous alumina suspensions, stabilized with an organic polyvalent salt dispersant called “Aluminon,” and including a poly(vinyl) alcohol (PVA) binder, are described in this study. It is observed that the addition of PVA, without any dispersant does not significantly influence the rheology. However, in the presence of the dispersant the rheology is affected significantly. At a given concentration of the dispersant, the viscosity, the storage and loss modulii all increase with the PVA concentration. Also, for a given concentration of the PVA, the viscosity, the storage and loss modulii values increases as the concentration of the dispersant is increased. At relatively low PVA concentrations, an excess concentration of the dispersant, causes flocculation of the particles in the suspension by a reduction of the electrostatic (double layer) effect. On the contrary, at higher concentrations of the PVA the flocculation of the suspension occurs via a depletion mechanism.     

不同品种巴旦杏仁中微量元素及总黄酮含量的比较研究

用火焰原子吸收光度法测定了6个品种巴旦杏仁中的K,Na,ca,Fe,cu,Zn,Mn,Mg等8种元素含量,并用紫外-可见分光光度法测定了总黄酮含量。结果表明,巴旦杏仁含有丰富的人体必需的微量元素,其中纸皮巴旦杏仁中K,Ca,Mn,Zn的含量普遍高于其它品种。微量元素测定方法的回收率在96．9％～101．7％之间,RSD值在0．74％～1．85％之间。总黄酮含量在不同品种之间呈现出较大差异,其中晚丰巴旦杏仁中总黄酮量高达1．75％,明显高于其它品种。为新疆巴旦杏资源的进一步研究和综合开发利用提供了新的科学依据。     

Numerical spectral examination of EMHD mixed convective flow of second-grade nanofluid towards a vertical Riga plate using an advanced version of the revised Buongiorno’s nanofluid model

Journal of Thermal Analysis and Calorimetry - Present communication aims to determine the impact of Cattaneo–Christov model and convective boundary on second-grade nanofluid flow alongside a...     

Facile Synthesis of 5-Aryl-N-(pyrazin-2-yl)thiophene-2-carboxamides via Suzuki Cross-Coupling Reactions,Their Electronic and Nonlinear Optical Properties through DFT Calculations

Synthesis of 5-aryl-N-(pyrazin-2-yl)thiophene-2-carboxamides (4a–4n) by a Suzuki cross-coupling reaction of 5-bromo-N-(pyrazin-2-yl)thiophene-2-carboxamide (3) with various aryl/heteroaryl boronic acids/pinacol esters was observed in this article. The intermediate compound 3 was prepared by condensation of pyrazin-2-amine (1) with 5-bromothiophene-2-carboxylic acid (2) mediated by TiCl₄. The target pyrazine analogs (4a–4n) were confirmed by NMR and mass spectrometry. In DFT calculation of target molecules, several reactivity parameters like FMOs (E_HOMO, E_LUMO), HOMO–LUMO energy gap, electron affinity (A), ionization energy (I), electrophilicity index (ω), chemical softness (σ) and chemical hardness (η) were considered and discussed. Effect of various substituents was observed on values of the HOMO–LUMO energy gap and hyperpolarizability. The p-electronic delocalization extended over pyrazine, benzene and thiophene was examined in studying the NLO behavior. The chemical shifts of ¹H NMR of all the synthesized compounds 4a–4n were calculated and compared with the experimental values.     

Caralluma tuberculata N.E.Br Manifests Extraction Medium Reliant Disparity in Phytochemical and Pharmacological Analysis

Solubility of phytoconstituents depends on the polarity of the extraction medium used, which might result in the different pharmacological responses of extracts. In line with this, ethnomedicinally important food plant (i.e., Caralluma tuberculata extracts) have been made in fourteen distinct solvent systems that were then analyzed phytochemically via total phenolic amount estimation, total flavonoid amount estimation, and HPLC detection and quantification of the selected polyphenols. Test extracts were then subjected to a battery of in vitro assays i.e., antioxidants (DDPH scavenging, antioxidant capacity, and reducing power estimation), antimicrobial (antibacterial, antifungal, and antileishmanial), cytotoxic (brine shrimps, THP-1 human leukemia cell lines and normal lymphocytes), and protein kinase inhibition assays. Maximum phenolic and flavonoid contents were computed in distilled water–acetone and acetone extracts (i.e., 16 ± 1 μg/mg extract and 8 ± 0.4/mg extract, respectively). HPLC-DAD quantified rutin (0.58 µg/mg extract) and gallic acid (0.4 µg/mg extract) in methanol–ethyl acetate and methanol extracts, respectively. Water–acetone extract exhibited the highest DPPH scavenging of 36 ± 1%. Total reducing potential of 76.0 ± 1 μg/mg extract was shown by ethanol chloroform while maximum total antioxidant capacity was depicted by the acetone extract (92.21 ± 0.70 μg/mg extract). Maximal antifungal effect against Mucor sp., antileishmanial, brine shrimp cytotoxicity, THP-1 cell line cytotoxicity, and protein kinase inhibitory activities were shown by ethyl acetate-methanol (MIC: 50 µg/disc), n-hexane (IC₅₀: 120.8 ± 3.7 µg/mL), ethyl acetate (LD₅₀: 29.94 ± 1.6 µg/mL), distilled water–acetone (IC₅₀: 118 ± 3.4 µg/mL) and methanol–chloroform (ZOI: 19 ± 1 mm) extracts, respectively. Our findings show the dependency of phytochemicals and bioactivities on the polarity of the extraction solvent and our preliminary screening suggests the C. tuberculata extract formulations to be tested and used in different ailments, however, detailed studies remain necessary for corroboration with our results.     

Alternative energy input: mechanochemical, microwave and ultrasound-assisted organic synthesis

Microwave, ultrasound, sunlight and mechanochemical mixing can be used to augment conventional laboratory techniques. By applying these alternative means of activation, a number of chemical transformations have been achieved thereby improving many existing protocols with superior results when compared to reactions performed under traditional conditions. The purpose of this critical review is to highlight the advances in this general area by presenting such newer applications in organic synthesis (175 references).     

Control of diameter,morphology, and structure of PVDF nanofiber fabricated by electrospray deposition

Poly(vinylidene fluoride) (PVDF) nanofibers were prepared by electrospray deposition (ESD). To control the diameter, morphology, and structure of PVDF nanofibers, some parameters were investigated, such as polymer concentration, nozzle‐to‐ground collector distance, feeding rate of the polymer solution, and applied voltage. The fabricated fiber was 80–700 nm in diameter. The increase in the polymer concentration caused an increase in the polymer viscosity and fiber diameter. At low polymer concentration (5 wt %), polymer nanoparticles were formed. An increase in applied voltage will increase the fiber diameter. Variation in the nozzle‐to‐ground collector distance did not result in significant changes in the fiber diameter. Increase in the feeding rate of the polymer solution decreased the fiber diameter. Differential scanning calorimetry (DSC) and wide angle X‐ray diffraction (WAXD) measurements showed that the melting point and total crystallinity were decreased. Fourier transform infrared spectroscopy (FTIR) measurement revealed that ESD process induced the formation of the oriented β‐phase PVDF structures. It was also demonstrated that the addition of hydrofluorocarbon solvent to polymer solution remarkably enhanced the formation of β‐phase crystalline structure of PVDF nanofiber. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 779–786, 2006     

Development of epitaxial silicon lattice-matched insulators: silicon heterostructures for quantum confinement

Epitaxial films of the wide-bandgap II–VI beryllium chalcogenide semiconductors, BeTe, BeSe, and BeSeTe were grown on arsenic-terminated silicon substrates by MBE. Silicon was also epitaxially regrown on Be-chalcogenide films. Initial structural characterization revealed the desired smooth two-dimensional nature of the layer growth. The composition of BeSeTe ternary films was governed by the Be/Se flux ratio during deposition rather than by the Se/Te flux ratio. The variation in Be/Se flux ratio or in the sticking coefficients due to temperature gradients led to radial compositional inhomogeneity. Current versus temperature measurements of the Be-chalcogenide films at elevated temperatures analyzed assuming thermionic emission over the heterojunction barrier, showed conduction band offsets of 1.2 eV for the BeSe_0.41Te_0.59/As/Si and 1.3 eV for the BeSe/As/Si heterostructures. At room temperature, current density through BeSe/Si and BeSe_0.41Te_0.59/Si films was mid-10 ^{− 9}A cm ^{− 2}at 0.1 MV cm ^{− 1}, similar to previously reported values for ZnS/Si, while BeTe/Si films had orders of magnitude higher current density, possibly due to interfacial recombination.     

Lithographically Cut Multiwalled Carbon Nanotubes: Opening Caps,Controlling Length Distribution,and Functionalization

This work presents a microwave digestion heating method using a 40 ml mixture of potassium permanganate and sulfuric acid (3/1 mol) to cut, end-open, and functionalize as-prepared multiwalled carbon nanotubes (A-MWCNTs). Also, the ability of the microwave digestion method was studied at different reaction times (5, 10, 20, 30, and 40 minutes). To harness the extent of treatment, shortened multiwalled carbon nanotubes (S-MWCNTs) were fully characterized by UV-visible, Fourier transform infrared spectroscopy, and Raman spectroscopies, as well as, transmission electron microscopy and optical microscopy. The results showed that, with this mild treatment, the A-MWCNTs (>80 µm) were efficiently and significantly shortened to below 1 µm after 40 minutes. Also, heating the closed reaction vessel under microwave irradiation at 90°C for 20 minutes was very effective in the functionalization of MWNTs. At the same time, the S-MWCNTs formed the best state of dispersion in water without the help of surfactants that provided possibility for further functionalizations. For the first 10 minutes, crystallinity increased then decreased until 20 minutes, and after that improved slightly. Finally, the mechanism of this process is explained schematically. This method could be used as high-efficiency and damage-free process to the cut, end-open, and functionalization of CNTs that led to dispersion of CNTs and ultimately for such application.      

Multifunctional Co3S4/Graphene Composites for Lithium Ion Batteries and Oxygen Reduction Reaction

Cobalt sulfide is a good candidate for both lithium ion batteries (LIBs) and cathodic oxygen reduction reaction (ORR), but low conductivity, poor cyclability, capacity fading, and structural changes hinder its applications. The incorporation of graphene into Co₃S₄ makes it a promising electrode by providing better electrochemical coupling, enhanced conductivity, fast mobility of ions and electrons, and a stabilized structure due to its elastic nature. With the objective of achieving high‐performance composites, herein we report a facile hydrothermal process for growing Co₃S₄ nanotubes (NTs) on graphene (G) sheets. Electrochemical impedance spectroscopy (EIS) verified that graphene dramatically increases the conductivity of the composites to almost twice that of pristine Co₃S₄. Electrochemical measurements indicated that the as‐synthesized Co₃S₄/G composites exhibit good cyclic stability and a high discharge capacity of 720 mA h g^?1 up to 100 cycles with 99.9 % coulombic efficiency. Furthermore, the composites react with dissolved oxygen in the ORR by four‐ and two‐electron mechanisms in both acidic and basic media with an onset potential close to that of commercial Pt/C. The stability of the composites is much higher than that of Pt/C, and exhibit high methanol tolerance. Thus, these properties endorse Co₃S₄/G composites as auspicious candidates for both LIBs and ORR.