Optical,structural characterization and dielectric relaxation of [C2H5NH3]2ZnCl4 compound

ABSTRACT

The new organic-inorganic compound [C₂H₅NH₃]₂ZnCl₄ has been grown by the slow evaporation at room temperature. The zero-dimensional (0-D) structure for this compound was determined by the single X-ray diffraction. It crystallizes at room temperature in the non-centrosymmetric space group Pna2₁ and consists of ethylammonium cations [C₂H₅NH₃]⁺ and [ZnCl₄]^2? tetrahedra anions. That is interconnected by means of hydrogen bonding contacts N-H···Cl. The molecular geometry and vibrational frequencies of [ZnCl₄]^2? and [C₂H₅NH₃]⁺ in the ground state was calculated using density functional method (B3LYP) with 6–31G(d) and 6–311G (d,p) basis set. The optimized geometric bond lengths and bond angles, obtained by using B3LYP/6–311G (d,p), show the best agreement with the experimental data. The optical absorbance was measured in order to deduce the absorption coefficient α, optical band gap E_g. The optical band gap is determined by extrapolating the plotted graph of (αhυ)^1/2 vs. (hυ). The large value of indirect optical band gap energy indicates the insulating nature of this material. Moreover, the extinction coefficient, refractive index and the dielectric permittivity of [C₂H₅NH₃]₂ZnCl₄ compound were calculated and the results are discussed. The evolution of the dielectric loss as a function of frequency revealed a distribution of relaxation times, probably ascribed to the reorientational dynamics of alkyl chains in this compound, and then analyzed with the Cole–Cole formalism.     

高分子金属微球的磁性能研究

在苯乙烯和丙烯酸共聚物「Ｐ（Ｓｔ－ｃｏ－ＡＡ）」，苯乙烯和４－乙烯吡啶共聚物「Ｐ（Ｓｔ－ｃｏ－４ＶＰ）Ｎｉ、Ｐ（Ｓｔ－ｃｏ－４ＶＰ）Ｃｏ金属微球，研究了它们的交流磁化率，磁滞回线，居里温度等磁性能。结果表明制得的了的微球为软磁材料，热重（ＴＧ）分析了则得Ｐ（Ｓｔ－ｃｏ－ＡＡ）Ｎｉ和Ｐ（Ｓｔ－ｃｏ－４ＶＰ）Ｎｉ的居时温度（Ｔｃ）分别为１７５℃和１８０℃，远远低于块状金属的居里温度值。     

Ba1-xSrxTi1-yMyO3固溶体的湿化学法合成与介电特性

为了提高 BaTiO3的室温介电常数和减少介电损失，目前工业上在电子元器件的制造过程中，采用固相掺杂方法，于 BaTiO3粉体中掺入适量锶、锆、锡和一些稀土元素的氧化物，以改善其性能。但由于固相掺杂的不均匀性，使得元器件的各项参数改善并不理想 [1]。近几年国外虽有用 Sol Gel法对 BaTiO3进行掺杂改性的研究 [2]，但却因为原材料价格昂贵而无法在我国生产。为此，本文率先用湿化学合成方法，在 100℃以下水溶液中对 BaTiO3进行了掺杂改性，使掺杂离子均匀进入母体晶格，合成了一系列 BaTiO3基固溶体纳米粉末，并对其介电特性进…     

Maxwell's Equations in Two-Phase Systems II: Two-Equation Model

The method of volume averaging is used to derive the two-equation model for Maxwell's equations in a two-phase system. The analysis provides a set of macroscopic transport equations for the electric and magnetic fields that are completely coupled in terms of the closure problem. When the closure problem is quasi-steady, a formal solution is obtained and estimates are developed for the differences between the averaged fields in the individual phases. These estimates lead to constraints for the condition of local electrodynamic equilibrium.     

Surface Functionalization at Atmospheric Pressure by DBD-Based Pulsed Plasma Polymerization

Dielectric barrier discharge (DBD)-based plasma deposition at atmospheric pressure, using glycidyl methacrylate (GMA, methacrylic acid-[2,3-epoxy-propyl ester]) as a prototype precursor was investigated in order to evaluate the applicability of dielectric barrier discharges to obtain plasma polymers with a high degree of structural retention of the starting precursor. Using pulsed excitation of the discharge, up to about 90% of the epoxy groups of GMA can be retained in plasma polymers obtainableat deposition rates in the order of 3–5nm/s. Preliminary investigations of the mechanism of film formation under pulsed plasma conditions indicate that the reaction of intact monomer molecules withsurface radicals generated during the pulses play a prominent role.     

用电介质镜像法计算线电荷与介质圆柱所形成的电场

利用电介质镜像法计算线电荷与介质圆柱体所形成的电场,给出电势与场强的解析表达式,进一步得出等势线与电场线方程,并利用软件MATLAB绘制出电场线和等势线(面)图予以验证.     

Synthesis and application of hypercrosslinked polymers with weak cation-exchange character for the selective extraction of basic pharmaceuticals from complex environmental water samples

The synthesis of high specific surface area sorbents (HXLPP-WCX) in the form of hypercrosslinked polymer microspheres with narrow particle size distributions, average particle diameters around 6 μm, and weak cation-exchange (WCX) character, is described. The WCX character arises from carboxylic acid moieties in the polymers, derived from the comonomer methacrylic acid. A novel HXLPP-WCX sorbent with an attractive set of chemical and physical properties was then used in an off-line solid-phase extraction (SPE) protocol for the selective extraction of a group of basic compounds from complex environmental samples, a priority being the clean separation of the basic compounds of interest from acidic compounds and interferences. The separation power of the new sorbent for basic pharmaceuticals was compared to two commercially available, mixed-mode sorbents, namely Oasis WCX and Strata-X-CW. Under identical experimental conditions, HXLPP-WCX was found to deliver both higher capacity and better selectivity in SPE than either of the two commercially available materials. In an optimised SPE protocol, the HXLPP-WCX sorbent gave rise to quantitative and selective extractions of low μg l⁻¹ levels of basic pharmaceuticals present in 500 ml of river water and 250 ml of effluent waste water.     

Thermal and Spectral Dielectric Properties of Polypyrrole/Polymethylmethacrylate Composites

Thermal properties of polypyrrole/polymethylmethacrylate (PPy/PMMA) composites were analyzed by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). A decrease in the glass transition temperatures with PPy concentration reveals the increase of segmental motion. The dielectric properties of these composites were studied for several weight concentrations of PPy in the frequency range between 500 Hz and 0.2 MHz, over the temperature range 23–110°C. Jonscher's phenomenological model has been used for modeling the dielectric response of the composite materials. This study shows that the results obtained for the dielectric response are in good agreement with the results of TGA and DSC measurements.     

Reversible addition‐fragmentation chain transfer polymerization of a typical hydrophobic monomer of styrene within microreactor of shell‐corona hollow microspheres suspending in water

Reversible addition‐fragmentation chain transfer (RAFT) polymerization of a typical hydrophobic monomer of styrene within microreactor of shell‐corona hollow microspheres of poly(styrene‐co‐methacrylic acid) suspending in water is studied. The shell‐corona hollow microspheres contain a hydrophilic corona of poly(methacrylic acid) (PMAA) and a cross‐linked polystyrene shell, which can suspend in water because of the hydrophilic corona of PMAA. The size of the shell‐corona hollow microspheres is about 289 nm and the extent of the microcavity of the hollow microsphere is 154 nm. These shell‐corona hollow microspheres can act as microreactor, within which the typical hydrophobic monomer of styrene, the RAFT agent of S‐benzyl dithiobenzoate and the initiator of 2,2′‐azobisisobutyronitrile can be encapsulated and RAFT polymerization of styrene takes place in well controlled manner in water. It is found that the resultant polymer of polystyrene has a competitively low polydispersity index and its number‐average molecular weight linearly increases with monomer conversion. The method is believed to be a new strategy of RAFT polymerization of hydrophobic monomer in aqueous solution. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Preparation and dielectric properties of the KBiScNbO6 double perovskite

Ceramic KBiScNbO₆ compound was synthesized for the first time. X‐ray diffraction analysis revealed that at room temperature the samples consist of a mixture of the perovskite and pyrochlore phases. The dominant phase is the perovskite one. This phase can be described as distorted pseudocubic Pm3m structure with unit‐cell parameter a_c = 4.069 Å. Rhombohedral distortion leading the polar R3m phase is assumed to be one of possible structural distortions. Dielectric measurements of the compound under study demonstrated anomalies associated with relaxor ferroelectric behavior (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)