Radiation grafted poly(vinylidene fluoride)-graft-polystyrene sulfonic acid membranes for fuel cells: Structure-property relationships

<正>Structure-property relationships for poly(vinylidene fluoride)-graft-polystyrene sulfonic acid(PVDF-g-PSSA) fuel cell membranes prepared by a single step method involving radiation-induced grafting of sodium styrene sulfonate(SSS) onto electron beam(EB) irradiated poly(vinylidene fluoride)(PVDF) films were established.The physico-chemical properties of the membranes such as ion exchange capacity,water swelling and proton conductivity were correlated with the degree of grafting(G,%) and the structural changes taking place in the membrane matrix during the preparation procedure. The variation in the crystallinity and the thermal stability of membranes was studied by differential scanning calorimetry (DSC) and thermogravimetric analysis(TGA),respectively.The membranes were found to undergo substantial structural changes in forms of ionic sites increase,hydrophilicity enhancement,hydrophobicity reduction and crystallinity decrease with the variation in G(%) and the preparation method.The structural and thermal properties of the obtained membranes were also compared with their counterparts prepared by a conventional two-steps method i.e.radiation induced grafting of styrene onto EB irradiated PVDF films followed by sulfonation.The PVDF-g-PSSA membranes obtained by a single-step method were found to have superior properties compared to those obtained by the conventional two-steps method.     

Electrical Behavior of the Insulator Class-E around Glass Transition: Experimental and Numerical Analyses

Currents flowing through semicrystalline polyethylene terephthalate (PET) film were measured over the temperature range 60°–100°C in electric fields from 24 × 10⁶ to 72 × 10⁶ V/m. A study of the influence of these external stresses on the electrical behavior of PET, at glass transition phase, permitted interpreting its response in terms of dipolar relaxation and movements of free charges. The simulation of the charging current around the glass transition temperature using a model consisting of the presence of bipolar carriers and one kind of permanent dipole with relaxation time τ allowed reproducing the experimental behavior. From this numerical calculation, space dependence of charge densities and field can be determined in order to explain the electrical behavior of current, which depends on parameters such as injection coefficient A _i , relaxation time τ, and mobility μ.     

Fabrication of nitrogen-enriched graphene oxide/Cu NPs as a highly efficient and recyclable heterogeneous nanocatalyst for the Chan–Lam cross-coupling reaction

Herein, we demonstrate the direct polymerization of melamine and cyanuric chloride in the surface of graphene oxide (GO) (N-enriched GO) in order to develop a new nanocatalyst. The supramolecular polymerized GO acts not only as a spacer to prevent the restacking of graphene sheets but also as a nitrogen source to generate active centers for Cu NP attachments. Subsequently, the nitrogen on the surface of the GO sheets coordinates with copper ions to generate copper nanoparticles. The prepared nanocatalyst was characterized by Fourier transform infrared spectroscopy, X-ray powder diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy and thermogravimetric analysis. This catalyst showed high efficiency and good activity in the Chan–Lam cross-coupling reaction of N-heterocycles and aniline derivatives with high yields in short reaction times. In addition, the nanocatalyst was easily recovered and reused for five consecutive runs without any noticeable loss of performance.     

Straightforward and highly efficient catalyst-free one-pot synthesis of dithiocarbamates under solvent-free conditions

[Structure: see text] A highly efficient and simple synthesis of dithiocarbamates is possible based on the one-pot reaction of amines, CS2, and alkyl halides without using a catalyst under solvent-free conditions. The mild reaction conditions, high yields, and broad scope of the reaction illustrate the good synthetic utility of this method. The reaction is a highly atom-economic process for production of S-alkyl thiocarbamates and successfully can be used in high quantities in the pharmaceutical or agrochemical industries.     

Soft Lattice and Defect Covalency Rationalize Tolerance of β‐CsPbI3 Perovskite Solar Cells to Native Defects

Although all‐inorganic metal halide perovskites (MHPs) have shown tremendous improvement, they are still inferior to the hybrid organic–inorganic MHPs in efficiency. Recently, a conceptually new β‐CsPbI₃ perovskite reached 18.4 % efficiency combined with good thermodynamic stability at ambient conditions. We use ab initio non‐adiabatic molecular dynamics to show that native point defects in β‐CsPbI₃ are generally benign for nonradiative charge recombination, regardless of whether they introduce shallow or deep trap states. These results indicate that MHPs do not follow the simple models used to explain defect‐mediated charge recombination in the conventional semiconductors. The strong tolerance is due to the softness of the perovskite lattice, which permits separation of electrons and holes upon defect formation, and only allows carriers to couple to the low‐frequency vibrations. Both factors decrease notably the non‐adiabatic coupling and slow down the dissipation of energy to heat.     

Study of the Influence of the Nature and Position of the Halogen Atom in the N-Halogenophenyl-2,5-dimethylpyrrole Upon the Vibrational (Hyper)polarizability: Theoretical Study

The two contributions, vibrational and electronic, to the electrical properties polarizability and first hyperpolarizability of the N-[(2, 3, or 4)-fluorophenyl]-2,5-dimethylpyrrole are evaluated theoretically at the HF/6-31G level within the double harmonic oscillator approximation. The calculations demonstrate that, with the exception of the second harmonic generation, the vibrational contribution to the first hyperpolarizability is important. However, the vibrational polarizability, contributes at most, 10% to the total electric polarizability. The analysis upon the sum-over-states expressions shows that there are only few modes which contribute strongly and, generally, have small vibrational energies. The effect of the fluorine substitution by an other substituent is also addressed.     

Correlation for Nusselt number in pure magnetic convection ferrofluid flow in a square cavity by a numerical investigation

Magnetic convection heat transfer in a two-dimensional square cavity induced by magnetic field gradient is investigated numerically using a semi-implicit finite volume method. The side walls of the cavity are heated with different temperatures, the top and bottom walls are isolated, and a permanent magnet is located near the bottom wall. Thermal buoyancy-induced flow is neglected due to the nongravity condition on the plane of the cavity. Conditions for the different values of non-dimensional variables in a variety of ferrofluid properties and magnetic field parameters are studied. Based on this numerical analysis, a general correlation for the overall Nusselt number on the side walls is introduced for a wide range of effective parameters. Results showed that maximum error produced by use of this correlation is about 6 percent.     

Synthesis and antiproliferative activity of (Z + E)‐1‐[4‐(2‐(cyclopentadienyltricarbonylmanganese)‐2‐oxo‐ethoxy)phenyl]‐1,2‐di(p‐hydroxyphenyl)‐but‐1‐ene against breast cancer cells

This paper describes the synthesis of (Z + E)‐1‐[4‐(2‐(cyclopentadienyltricarbonylmanganese)‐2‐oxo‐ethoxy)phenyl]‐1,2‐di(p‐hydroxyphenyl)‐but‐1‐ene. Two synthetic pathways were explored. The best pathway consisted of the alkylation of 1,2‐bis‐[4‐(tert‐butyl‐dimethylsilyloxy)phenyl]‐1‐(4‐hydroxyphenyl)but‐1‐ene with BrCH₂COOEt. The ester obtained was transformed into the Weinreb amide by reaction with HN(OMe)Me–HCl. The reaction of lithium manganese tricarbonylcyclopentadienide with the Weinreb amide produced 1‐[4‐(2‐(cyclopentadienyltricarbonylmanganese)‐2‐oxo‐ethoxy)phenyl]‐1,2‐di(p‐tert‐butyldimethylsiloxyphenyl)‐but‐1‐ene. The deprotection of phenolic functions of the latter compound led to the formation of the final compound. The Z and E isomers could be separated but the isomerization of these isomers from one to another is an easy process. The Z + E compound 2 was tested against the hormone‐dependent MCF‐7 and hormone‐independent MDA‐MB‐231 breast cancer cell lines. The IC₅₀ values of compound 2 were 4.80 ± 2.00 µm and 4.79 ± 0.70 µm for MCF‐7 cells and MDA‐MB‐231 cells, respectively, which was three times better than the ferrocenyl analogue. Copyright © 2012 John Wiley & Sons, Ltd.     

Transportation and Settling Distribution of Microparticles in Low-Reynolds-Number Poiseuille Flow in Microchannel

In this article, velocity field and settling distribution of microparticles in a dilute suspension in low-Reynolds-number Poiseuille flow in a microchannel is experimentally investigated using microscopic image analysis. An effective technique is applied to manipulate single-particle tracking in order to determine the controlling parameters on transportation and settling of microparticles in microchannels. The results show that the velocities of dispersed phase are affected by the hydrodynamic properties, and this velocity deviation can be significant when the hydrodynamic coupling between particles and channel walls is considerable. Increasing the Reynolds number would result in decrease in total number of particles settled on the bottom wall of channel.     

Microwaves in organic synthesis: Facile synthesis of biologically active pyridazinone and iminopyridazine derivatives

Condensation of Wittig reagents 1a,b with arylhydrazones 2a,b by conventional and by microwave heating techniques furnished the corresponding pyridazines 3a‐e . The arylhydrazones 7a,b were allowed to react with 1a,b under the same conditions to produce the pyridazinones 10a,b and iminopyridazines 11a,b respectively. On the other hand, the arylhydrazones 12a‐c reacted with 1a to afford the pyridazinones 13a‐c . Treatment of 3b with dimethylformamide dimethyl acetal (DMFDMA) produced the adduct 15 . The utility of microwave heating technique led to the reduction of the reaction times to few minutes and to the improvement of the yields of the products. The in vitro biological activity of some newly prepared compounds against four types of fungi was studied.