Synthesis of inorganic-organic hybrids by incorporation of inorganic components into organic polymer using metal alkoxides

Inorganic-organic hybrids have been synthesized by incorporation of the inorganic component of Ti(OC₂H₅)₄ into the organic polymer of ethyl cellulose. The inorganic-organic hybrids did not dissolve in toluene used as a solvent for the starting materials. The ethanol was formed as a by-product of the alcoholysis condensation reaction between Ti(OC₂H₅)₄ and ethyl cellulose. These results suggest that ethoxy groups of Ti(OC₂H₅)₄ react with hydroxy groups of ethyl cellulose to form cross-linking bonds of –O–Ti–O–. The reaction of Ti(OC₂H₅)₄ with ethyl cellulose was further investigated by Fourier transform infrared (FT-IR) spectroscopy. The FT-IR spectroscopic experiments revealed that the Ti–O bond state of Ti(OC₂H₅)₄ was changed by refluxing a toluene solution of Ti(OC₂H₅)₄ with ethyl cellulose. The inorganic-organic hybrids have an interesting dielectric property; their dielectric constant is higher than that of ethyl cellulose and that of a simple mixture of TiO₂ and ethyl cellulose.     

CaTiO3纳米粉体溶胶-凝胶法合成、表征及介电特性

采用无机盐溶胶-凝胶法制备了CaTiO₃纳米粉体，采用TG-DTA、XRD、TEM等技术进行了表征，并探讨了CaTiO₃纳米粉体烧结特性及介电效应。结果表明，干凝胶800 ℃低温煅烧可获得粒径分布较窄、平均粒径为60～70 nm的单相CaTiO₃纳米粉。纳米CaTiO₃粉具有较大的比表面积，使作为粉体烧结驱动力的表面能剧增，促使CaTiO₃在1 200 ℃实现致密烧结，比固相法制备的微米粉烧结降低100～200 ℃，且具有较宽的烧结温区。与微米级粉体烧结体介电特性相比，纳米粉具有更高的Q_f值。纳米CaTiO₃粉制备的陶瓷在1 250 ℃烧结2 h，获得优良的介电性能：ε_r=172，Q_f=4 239 GHz，τ_f=+7.68 × 10^-4 ℃^-1。     

聚苯胺／聚乙烯醇导电复合膜的制备及性质研究

用较简单的化学氧化现场吸附聚合法（ｉｎ－ｓｉｔｕｐｏｌｙｍｅｒｉｚａｔｉｏｎ）制得了聚苯胺（ＰＡｎ）／聚乙烯醇（ＰＶＡ）导电复合膜．该膜具有较好的导电性和机械性能；其电导率可达５．８ｓ／ｃｍ，拉伸强度达１３ＭＰａ，断裂伸长率为１１０％左右．本文讨论了制备的各种条件对复合膜导电性能及力学性能的影响、稳定性及电化学活性；并采用循环伏安曲线、扫描电镜（ＳＥＭ）、ＦＴＩＲ谱及元素分析对该复合膜的结构和性能进行了表征．     

A novel microwave dielectric ceramic Ca2Zn4Ti16O38: Preparation and dielectric properties

A novel microwave dielectric powder with composition of Ca₂Zn₄Ti₁₆O₃₈ was synthesized through a citrate sol-gel process. The development of crystalline phases with heat-treating temperature for the gel derived powders was evaluated by using thermo-gravimetric analysis and X-ray powder diffraction analysis techniques. The pure phase of Ca₂Zn₄Ti₁₆O₃₈ with crichtonite crystal structure was obtained at relatively low temperature of 1000 °C. The synthesized powder has high reactivity and the dense ceramics with single crystalline phase were obtained at low sintering temperature of 1100 °C. Impedance spectroscopy and microwave dielectric measurements on sintered samples showed the present compound to be a modest dielectric insulator with excellent dielectric properties of ε_r∼47-49, Qf value ∼27,800-31,600 GHz and τ_f∼+45 to +50 ppm/°C. It shows comparable microwave dielectric properties to other moderate-permittivity microwave dielectrics, but much lower sintering temperature of 1100 °C.     

Dielectric analysis of polystyrene microcapsules using scanning dielectric microscope

 A dielectric imaging technique with a scanning dielectric microscope was applied to polystyrene microcapsules in an aqueous environment to study the electrical properties of individual ones. The dielectric images obtained over a frequency range from 10 kHz to 10 MHz showed frequency dependence, which indicated dielectric dispersion (or relaxation) due to interfacial polarization or the build up of charge on the boundaries between the microcapsule shell and the aqueous phases. The dielectric dispersion was analyzed based on an equivalent electrical circuit model and a shell-sphere model in which a spherical core is covered with an insulating shell. Received: 26 September 1997 Accepted: 26 December 1997     

A novel technique to measure the surface electrical potential of polymer films by using dielectric spectroscopy

A novel method that allows the determination of the electrical potential of a polymer surface has been applied for polypropylene film treated by N₂ + H₂ cold plasma. The plasma treatment results in formation on the film surface of NH₂ groups, which then gets transformed to NH₃⁺ in contact with an electrolyte and leads to the formation of an electrical double layer. The method consists of theoretical calculation of electrical model potential, using the measurement of the electrical capacitance of the film in contact with an electrolyte by dielectric spectroscopy. Comparison with the results obtained by theoretical model shows similar dependencies of the electrical potential as a function of amino‐groups density and electrolyte concentration, but systematic differences of absolute values are observed. Copyright © 2005 John Wiley & Sons, Ltd.     

Rigid nanoscopic containers for highly dispersed, stable metal and bimetal nanoparticles with both size and site control

We demonstrate a novel strategy for the preparation of mesoporous silica-supported, highly dispersed, stable metal and bimetal nanoparticles with both size and site control. The supporting mesoporous silica, functionalized by polyaminoamine (PAMAM) dendrimers, is prepared by repeated Michael addition with methyl acrylates (MA) and amidation reaction with ethylenediamine (EDA), by using aminopropyl-functionalized mesoporous silica as the starting material. The encapsulation of metal nanoparticles within the dendrimer-propagated mesoporous silica is achieved by the chemical reduction of metal-salt-impregnated dendrimer-mesoporous silica by using aqueous hydrazine. The site control of the metal or bimetal nanoparticles is accomplished by the localization of inter- or intradendrimeric nanoparticles within the mesoporous silica tunnels. The size of the encapsulated nanoparticles is controlled by their confinement to the nanocavity of the dendrimer and the mesopore. For Cu and Pd, particles locate at the lining of mesoporous tunnels, and have diameters of less than 2.0 nm. For Pd/Pt, particles locate at the middle of mesoporous tunnels and have diameters in the range of 2.0-4.2 nm. The Pd and Pd/Pt nanoparticles are very stable in air, whereas the Cu nanoparticles are stable only in an inert atmosphere.     

Measurement of moisture in grains at extreme temperatures

Summary This research has demonstrated that the dielectric method can be used successfully for grain moisture measurements for diverse grain types over wide ranges of temperatures if the grain moisture content is below certain (grain-specific) threshold values. These high-moisture limits were estimated. Optimum temperature correction coefficients for 149 MHz moisture measurements were determined for grain samples at different moisture levels. This information should be very helpful for grain moisture meter manufacturers and for moisture meter users who need to determine grain moisture contents at temperature extremes to be able to market grain more efficiently.     

明胶中α组分含量对明胶/羟基磷灰石复合材料力学性能的影响

选用α组分含量分别为20.5%,41%和50%的A、B、C 3种明胶作为原料,采用同时加入法制备了明胶/羟基磷灰石(HAP)复合材料.通过对干态复合物膜拉伸性能的测试和对比,发现,明胶α组分含量的变化对复合材料的弹性模量影响较大,而对拉伸强度和断裂伸长率的影响则相对较小,但总的来说,三者均随α组分含量的增加而增大.其中,α组分含量最高的复合物C的拉伸强度为86.40 MPa,弹性模量为2682.35 MPa,断裂伸长率为8.65%.另外,对复合物C基本性质的表征结果表明,该材料具有类似于自然骨的组成和结构性质,因此有望成为一种具有优异力学性能的骨替代材料.     

Ion Association and Hydration in Aqueous Solutions of Nickel(II) and Cobalt(II) Sulfate

Aqueous solutions of nickel(II) and cobalt(II) sulfate have been investigated at 25 ^∘C by dielectric relaxation spectroscopy (DRS) over a wide range of frequencies (0.2 ≤ ν (GHz) ≤ 89) and salt concentrations (0.025 ≤ c(mol-L⁻¹) ≤ 1.4). The spectra indicate, as for MgSO₄(aq) studied previously, the simultaneous presence of double solvent-separated, solvent-shared and contact ion pairs in both NiSO₄(aq) and CoSO₄(aq). The stepwise formation constants for each ion-pair type and the overall association constant, obtained from the data are in good agreement with ultrasonic relaxation and other estimates. The DR spectra at higher concentrations (c ≥ 0.5 mol-L⁻¹) suggest the existence of a nonlinear triple ion M₂SO₄²⁺(aq). Consistent with the very strong hydration of the salts, which have ‘effective’ hydration numbers approaching 27 at infinite dilution, there are no significant differences in any of the relaxation or thermodynamic parameters for NiSO₄(aq) and CoSO₄(aq), except that the triple ion appears to be somewhat more stable for the latter.