聚偏氟乙烯-磺化聚醚砜相容性及其成膜性能

研究了聚偏氟乙烯(PVDF)-磺化聚醚砜(SPES)的相容性及其成膜性能.首先通过溶解度参数、粘度法和目测法研究共混溶液的相容性,接着采用浊度法测定了共混溶液的热力学性质,最后采用浸没沉淀法制备了共混膜并探讨了成膜性能.结果显示,PVDF和SPES为部分相容体系,随着SPES含量的增加,共混溶液相容性逐渐减小,当SPES含量增加到50wt%时,体系发生分相.共混溶液的成膜性能良好,SPES含量增加有利于体系发生液液分相,生成高孔隙率膜,并且极大的提高了PVDF膜的亲水性和水通量.     

Copolymerization of vinylidene difluoride with hexafluoropropene in supercritical carbon dioxide

Vinylidene difluoride and hexafluoropropene are copolymerized in supercritical carbon dioxide at 280 bar and 50 °C by means of free radical copolymerization, initiated by diethyl peroxydicarbonate. The first stages of the reaction were monitored by turbidity measurements and the time/conversion curve was followed gravimetrically to measure the initial rates of polymerization. The obtained copolymers possessed bimodal molecular weight distributions, their average comonomer composition was well described by the Lewis‐Mayo equation with the copolymerization parameters r_VDF = 4.8 and r_HFP = 0. The glass transition and melting temperatures of the copolymers are similar to that of the materials resulting from aqueous emulsion polymerization. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1299–1316, 2006     

The silica-like extended polymorphism of cobalt(II) imidazolate three-dimensional frameworks: X-ray single-crystal structures and magnetic properties

Five polymorphous frameworks of cobalt(II) imidazolates (1-5) have been prepared by solvatothermal syntheses. Of these, compound 3 has already been synthesized in a gas-phase reaction by Seel et al. in 1969 and structurally characterized by Sturm et al. in 1975. The new synthetic strategy affords four polymorphous frameworks of cobalt(II) imidazolates (1, 2, 4, 5) of crystalline substances, of which the compound 4 (a = b = 23.450(3), c = 12.460(3) A, tetragonal, I4(1)cd, Z = 16) is an isomorphous compound of [Zn(im)(2)]( infinity ), which was also synthesized in a gas-phase reaction in 1980. The frameworks of compounds 1 and 2 are porous and isostructural; they have the same framework topology that represents a novel uninodal (6,4)-net: 1: a = 18.513(4), b = 24.368(5), c = 9.2940(19) A, orthorhombic, Fdd2, Z = 16; 2: a = 17.635(4), b = 27.706(6), c = 9.0810(18) A, orthorhombic, Fdd2, Z = 16. The framework of compound 5 exhibits a topology of zeolitic structure with the unit-cell parameters: a = 24.3406(8), b = 9.4526(3), c = 24.8470(8) A, beta = 91.977(1) degrees, monoclinic, P2(1)/n, Z = 4. All polymorphous frameworks of cobalt(II) imidazolates reflect the structural features of silica (SiO(2)) and also exhibit different magnetic behaviors, although the imidazolates transmit the antiferromagnetic coupling between the cobalt(II) ions in all cases. However, the uncompensated antiferromagnetic couplings arise from spin-canting are sensitive to the structures: compound 1 is an antiferromagnet with T(N) = 13.11 K; compounds 2-4 are weak ferromagnets (canted antiferromagnets): 2 shows a very weak ferromagnetism below 15 K, 3 exhibits a relatively strong ferromagnetism below 11.5 K and a coercive field (H(C)) of 1800 Oe at 1.8 K, and 4 displays the strongest ferromagnetism of the three cobalt imidazolates and demonstrates a T(C) of 15.5 K with a coercive field, H(C), of 7300 Oe at 1.8 K. However, compound 5 seems to be a hidden canted antiferromagnet with a magnetic ordering temperature of 10.6 K.     

Surfactant-directed polypyrrole/CNT nanocables: synthesis, characterization, and enhanced electrical properties.

We describe here a new approach to the synthesis of size-controllable polypyrrole/carbon nanotube (CNT) nanocables by in situ chemical oxidative polymerization directed by the cationic surfactant cetyltrimethylammonium bromide (CTAB) or the nonionic surfactant polyethylene glycol mono-p-nonylphenyl ether (Opi-10). When carbon nanotubes are dispersed in a solution containing a certain concentration of CTAB or Opi-10, the surfactant molecules are adsorbed and arranged regularly on the CNT surfaces. On addition of pyrrole, some of the monomer is adsorbed at the surface of CNTs and/or wedged between the arranged CTAB or Opi-10 molecules. When ammonium persulfate (APS) is added, pyrrole is polymerized in situ at the surfaces of the CNTs (core layer) and ultimately forms the outer shell of the nanocables. Such polypyrrole/CNT nanocables show enhanced electrical properties; a negative temperature coefficient of resistance at 77-300 K and a negative magnetoresistance at 10-200 K were observed.     

Structural,magnetic and electrical properties of Fe substituted GdCrO3

Single phase samples of bulk GdCr_1-xFe_xO₃ were prepared for x = 0 to 0.50. The lattice parameters obtained from Rietveld refinement based on Pbnm space group show that they increase systematically with Fe concentration, i.e. with a = 5.3145 Å, b = 5.5249 Å and c = 7.6068 Å for x = 0 to a = 5.3330 Å, b = 5.5670 Å, and c = 7.6382 Å for x = 0.50. Magnetization measurement shows that all samples exhibit antiferromagnetic transition. Their Neel temperature (T_N) gradually decreases upto x = 0.20 and beyond that it increases quite sharply due to considerable concentration of Fe³⁺ – O²⁻ – Fe³⁺ networks. The magnetization reversal observed in the parent compound (GdCrO₃) is found to be suppressed upon Fe substitution and however for x = 0.40, magnetic compensation is observed at T_comp = 125 K. They are explained by considering the variation in the magnitude of weak ferromagnetic moment for different Fe concentrations. Complex impedance spectra measured at different temperatures above room temperature show the thermally activated relaxation of charge carriers with contribution from both grains and grain boundaries. The relaxation frequency of charge carriers and dc conductivity follow the Arrhenius law with comparable activation energy values.     

Structural, electrical and electron spin resonance properties of CoCl2-filled polyvinylidene fluoride films

Polyvinylidene fluoride (PVDF) films, filled with mass fractions w≤15% of CoCl₂, were prepared. The X-ray diffraction (XRD) scans evidenced semicrystalline structures containing - and/or β-PVDF phases. IR spectra confirmed these findings, and revealed some structural defects such as mono- and di-fluorinated alkenes and head-to-head segments. The optical absorption spectra suggested the presence of: (a) two optical gaps (one of them, Eg₂, depends on W); (b) tetrahedral Co(II) coordination for all of the filling levels (FL); and (c) octahedral Co(II) forms at 15% FL. The electrical resistivity results are discussed on the basis of the modified interpolaron hopping model of Kuivalainen et al., Phys Rev 1985;B31:7900. The temperature and FL dependences of the calculated hopping distance (R_o) are discussed. It is implied that the difluorinated alkenes exert a significant influence on Eg₂ and R_o. The electron spin resonance (ESR) spectra confirmed the optical absorption implications.     

Structural,morphological and magnetic properties of nano-crystalline zinc substituted cobalt ferrite system

Nano-crystalline zinc-substituted cobalt ferrite powders, Co_1−xZn_xFe₂O₄ (x = 0, 0.25, 0.5, 0.75 and 1), have been synthesized by the combustion route. The structural, morphological and magnetic properties of the products were determined and characterized in detail by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and vibrating sample magnetometer (VSM). X-ray analysis showed that the samples were cubic spinel. The increase in zinc concentration resulted in an increase in the lattice constant, unit cell volume, X-ray density, ionic radii, the distance between the magnetic ions and bond lengths on tetrahedral sites and octahedral sites of cubic spinel structure. Opposite behavior was observed for the average crystallite size of the as synthesized solids. The variation of saturation magnetization (M_s) value of the samples was studied. The maximum saturation magnetization value of the Co_o.25Zn_0.75Fe₂O₄ sample reached 76.87 emu/g. The high saturation magnetization of these samples suggests that this method is suitable for preparing high-quality nano-crystalline magnetic ferrites for practical applications.     

Structural,magnetic, and vibrational properties of stoichiometric clusters of CrN

We performed density‐functional‐theoretic calculations to investigate the structural, magnetic and vibrational properties of the stoichiometric clusters (CrN)_n ( ). We show that the building block of the ground‐state structures of these clusters is a square CrNCrN unit; the only exception with n > 2 occurs for (CrN)₃, but this cluster has an isomer not very far in energy from the ground state consisting of a pair of CrNCrN squares sharing a CrN bond. In the smaller CrN, (CrN)₂, and (CrN)₃ clusters the magnetic moments of the N atoms are non‐negligible and antiparallel to those of the Cr atoms, but for the larger species (CrN)₄, (CrN)₅, (CrN)₆, and (CrN)₉ the cluster magnetic moments are almost entirely due to the Cr atoms. Lack of imaginary vibrational frequencies in the predicted ground‐state structures of (CrN)_n ( ) confirms that they are mechanically stable equilibrium states. © 2015 Wiley Periodicals, Inc.     

Reactions of isocyanatophosphoryl difluoride with π-abundant nitrogen heterocycles and carbonyl compounds

Reactions of electron-rich nitrogen heterocycles with isocyanatophosphoryl difluoride were studied. Novel heteroylaminophosphoryl difluorides were obtained in high yields. N-Phosphorylated imines were synthesized for the first time from carbonyl compounds and phosphorus isocyanates. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 564–566, March, 2006.     

Synthesis,characterization, and preceramic properties of π‐conjugated polymers based on Ni(II) complexes of goedken's macrocycle

Nickel(II) complexes of Goedken's macrocycle bearing alkyne substituents were copolymerized with 2,7‐dibromo‐9,9‐dihexylfluorene, 2,5‐dibromo‐3‐hexylthiophene, and 1,4‐dibromo‐2,5‐bis(hexyloxy)benzene via microwave‐induced Sonogashira cross‐coupling reactions to produce copolymers 6F , 6T , and 6B . The spectroscopic and electrochemical properties of the copolymers were examined and compared to model compounds. Specifically, each polymer exhibited a nickel‐based absorption centered at about 589 nm and two π → π* transitions between 272 and 387 nm. While the copolymers did not exhibit extended π conjugation, the nature of the organic spacer did affect the high energy transitions. Furthermore, each copolymer underwent two ligand‐based one‐electron oxidations at potentials of about 0.24 V and about 0.75 V relative to the ferrocene/ferrocenium redox couple. Postpolymerization functionalization of the alkyne group in 6F with Co₂(CO)₈ afforded a novel heterobimetallic copolymer that yielded amorphous nanomaterials containing Ni/Co when pyrolyzed at 800 °C for 3 h under an atmosphere of N₂/H₂ (95:5). © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3257–3266     

Automated polyvinylidene difluoride hollow fiber liquid-phase microextraction of flunitrazepam in plasma and urine samples for gas chromatography/tandem mass spectrometry

A new polyvinylidene difluoride (PVDF) hollow fiber (200 μm wall thickness, 1.2 mm internal diameter, 0.2 μm pore size) was compared with two other polypropylene (PP) hollow fibers (200, 300 μm wall thickness, 1.2 mm internal diameter, 0.2 μm pore size) in the automated hollow fiber liquid-phase microextraction (HF-LPME) of flunitrazepam (FLNZ) in biological samples. With higher porosity and better solvent compatibility, the PVDF hollow fiber showed advantages with faster extraction efficiency and operational accuracy. Parameters of the CTC autosampler program for HF-LPME in plasma and urine samples were carefully investigated to ensure accuracy and reproducibility. Several parameters influencing the efficiency of HF-LPME of FLNZ in plasma and urine samples were optimized, including type of porous hollow fiber, organic solvent, agitation rate, extraction time, salt concentration, organic modifier, and pH. Under optimal conditions, extraction recoveries of FLNZ in plasma and urine samples were 6.5% and 83.5%, respectively, corresponding to the enrichment factor of 13 in plasma matrix and 167 in urine matrix. Excellent sample clean-up was observed and good linearities (r² = 0.9979 for plasma sample and 0.9995 for urine sample) were obtained in the range of 0.1–1000 ng/mL (plasma sample) and 0.01–1000 ng/mL (urine sample). The limits of detection (S/N = 3) were 0.025 ng/mL in plasma matrix and 0.001 ng/mL in urine matrix by gas chromatography/mass spectrometry/mass spectrometry.     

Zinc and cobalt complexes with (2-carboxyphenoxy) acetic acid ligand: syntheses,structures, fluorescent and magnetic properties

Four binary compounds, [Zn(cpa)(H₂O)₃] (1), [Co(cpa)(H₂O)₃] (2), [Zn(cpa)(H₂O)]_n, (3) and [Co(cpa)(H₂O)]_n (4) (H₂cpa = (2-carboxyphenoxy)acetic acid), have been synthesized and structurally characterized. In mononuclear 1 or 2, the metal ion (Zn^II for 1 and Co^II for 2) is surrounded by three water molecules and one tridentate chelate cpa^2? in a distorted octahedral geometry, while in 3 or 4, the central metal ion (Zn^II for 3 and Co^II for 4) is located in a deformed square–pyramid formed by one water and two cpa^2?. Each cpa^2? is chelate bridging μ₂ coordination and forms a 1-D zigzag chain structure 2 or 3. The different synthesis conditions for 1–4 have been carefully discussed. The solid-state fluorescence measurements for 1 and 3 together with magnetic properties for 4 also have been investigated.     

Structural and magnetic properties of Zn-substituted cobalt ferrites prepared by co-precipitation method

Zn substituted cobalt ferrite spinels with the general formula Zn(x)Co(1-x)Fe(2)O(4) (with x varying from 0 to 0.5) were synthesized by a co-precipitation method and calcined at 500 °C and 800 °C. It was found that Zn substitution has a big effect in decreasing the Curie temperature (T(c)), from around 440 °C for the undoped sample to ~180 °C with x = 0.5. However, these values were also strongly affected by the pre-calcination temperature of the samples, thus T(C) shifts from ~275 °C for the x = 0.3 sample to ~296 °C after calcination at 500 °C and 800 °C respectively. These effects are due to facilitation of demagnetisation by substitution of the non-magnetic Zn ions and by production of very small nanoparticles. The latter are removed by higher temperature calcinations and so T(C) increases.     

Synthesis,characterization, thermal,electrical and magnetic properties of polyaniline composites with rare earth gadolinium coordination complex

Novel polyaniline/gadolinium (PANI/Gd) composites were successfully synthesized by “in‐situ” polymerization at the presence of rare earth Gd coordination complex and D‐tartaric acid (an a dopant). It is rarely to find the studies on related field to add rare earth Gd coordination complex as fillers. Fourier transform infrared (FTIR) spectra, X‐ray diffraction (XRD) and scanning electron microscope (SEM) were used to examine the structure and surface appearance characterization of materials. The thermal stability performance of composites was investigated by thermogravimetry and derivative thermogravimetry (TG‐DTG). Electrochemical performance was measured by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge–discharge test. The magnetic property was investigated by physical property measurement system (PPMS). The structure and surface appearance characterization and the magnetic properties jointly demonstrate the polymerization of rare earth Gd coordination complex and PANI–D‐tartrate (DTA) not only simple physical mixing but also chemical mixing. TG‐DTG analysis suggests that thermal stability of PANI/Gd composites is higher than that of PANI–DTA. Electrochemical performance tests and SEM indicate that the composite (PANI/Gd = 3.3:1,mass ratio) has the most regular morphology and best specific capacitance. The magnetization of the composite (PANI/Gd = 3.3:1,mass ratio)is evidently smaller compared with PANI–DTA and rare earth Gd coordination complex. Copyright © 2016 John Wiley & Sons, Ltd.     

Polyhedral magnetite nanocrystals with multiple facets: facile synthesis, structural modelling, magnetic properties and application for high capacity lithium storage

Polyhedral magnetite nanocrystals with multiple facets were synthesised by a low temperature hydrothermal method. Atomistic simulation and calculations on surface attachment energy successfully predicted the polyhedral structure of magnetite nanocrystals with multiple facets. X-ray diffraction, field emission scanning electron microscopy, and high resolution transmission microscopy confirmed the crystal structure of magnetite, which is consistent with the theoretical modelling. The magnetic property measurements show the superspin glass state of the polyhedral nanocrystals, which could originate from the nanometer size of individual single crystals. When applied as an anode material in lithium ion cells, magnetite nanocrystals demonstrated an outstanding electrochemical performance with a high lithium storage capacity, a satisfactory cyclability, and an excellent high rate capacity.