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Chemistry Method (chemistry + method)

Distribution by Scientific Domains

Polymers and Materials Science	50%
Chemistry	50%

Selected Abstracts

Silver Surface Iodination for Enhancing the Conductivity of Conductive Composites

ADVANCED FUNCTIONAL MATERIALS, Issue 16 2010
Cheng Yang
Abstract The electrical conductivity of a silver microflake-filled conductive composites is dramatically improved after a filler surface treatment. By a simple iodine solution treatment, nonstoichiometric silver/silver iodide nanoislands form on the silver filler surface. Evidence of the decrease of surface silver oxide species is provided by TOF-SIMS and the redox property of the nanoclusters is studied using cyclic voltammetry and TOF-SIMS depth profile analyses. The redox property of the nanoclusters on silver flakes helps enhance the electrical conductivity of the conductive composites. The electrical resistivity of the improved conductive composites is measured by four-point probe method; the reliability of the printed thin film resistors is evaluated by both the 85 °C/85% relative humidity moisture exposure and the ,40 , 125 °C thermal cycling exposure. The conductive composite printed radio frequency identification (RFID) antennas with 27.5 wt% of the modified silver flake content show comparable performance in the RFID tag read range versus copper foil antennas, and better than those commercial conductive adhesives that require much higher silver content (i.e., 80 wt%). This work suggests that a surface chemistry method can significantly reduce the percolation threshold of the loading level of the silver flakes and improve the electrical conductivity of an important printed electronic passive component. [source]

Silver Surface Iodination for Enhancing the Conductivity of Conductive Composites

Reaction pathways of propene pyrolysis

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 7 2010
Yena Qu
Abstract The gas-phase reaction pathways in preparing pyrolytic carbon with propene pyrolysis have been investigated in detail with a total number of 110 transition states and 50 intermediates. The structure of the species was determined with density functional theory at B3PW91/6-311G(d,p) level. The transition states and their linked intermediates were confirmed with frequency and the intrinsic reaction coordinates analyses. The elementary reactions were explored in the pathways of both direct and the radical attacking decompositions. The energy barriers and the reaction energies were determined with accurate model chemistry method at G3(MP2) level after an examination of the nondynamic electronic correlations. The heat capacities and entropies were obtained with statistical thermodynamics. The Gibbs free energies at 298.15 K for all the reaction steps were reported. Those at any temperature can be developed with classical thermodynamics by using the fitted (as a function of temperature) heat capacities. It was found that the most favorable paths are mainly in the radical attacking chain reactions. The chain was proposed with 26 reaction steps including two steps of the initialization of the chain to produce H and CH3 radicals. For a typical temperature (1200 K) adopted in the experiments, the highest energy barriers were found in the production of C3 to be 203.4 and 193.7 kJ/mol. The highest energy barriers for the production of C2 and C were found 174.1 and 181.4 kJ/mol, respectively. These results are comparable with the most recent experimental observation of the apparent activation energy 201.9 ± 0.6 or 137 ± 25 kJ/mol. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010 [source]

Synthesis and Characterization of Highly Dispersed Antimony-Doped Stannic Hydroxide Nanoparticles: Effects of the Azeotropic Solvents to Remove Water on the Properties and Microstructures of the Nanoparticles

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2007
Fen Yang
Highly dispersed antimony (Sb)-doped stannic hydroxide nanoparticles have been successfully prepared using the solution chemistry method. The properties and microstructures of the nanoparticles are investigated in detail by means of infrared, transmission electron microscope, X-ray diffractometer, and Brunauer-Emmett-Teller nitrogen surface area measurements. The results indicate that the properties and microstructures of the nanoparticles strongly depend on the azeotropic solvents used to remove water at the drying stage. Various azeotropic solvents are screened to investigate their effects on the size and dispersivity of dried Sb-doped stannic hydroxide. Three empirical rules are drawn for selecting an effective azeotropic solvent: (1) the solvent molecule should contain at least one atom such as oxygen as the hydrogen (H)-bond acceptor to form H bonds with the surface ,OH (acting as an H-bond donor) of polymer particle; (2) the H-bond acceptor should locate in the middle of the alkane chain rather than on the terminal so that the alkane chain can stretch out and cover more surface area, improving the dispersivity of the dried product; and (3) the solvent should have a higher boiling point (,140°C) to reduce the time of azeotropic distillation for removing water and maintain a lower residual amount of azeotropic agent. Based on the empirical rules, it is discovered that iso-amyl acetate is the most effective azeotropic solvent. [source]

Second-order Scattering and Frequency Doubling Scattering Spectra of Thallium(III)-Methotrexate System and Its Analytical Application

CHINESE JOURNAL OF CHEMISTRY, Issue 9 2008
Cun-Xian XI
Abstract In pH 4.9 Britton-Robinson buffer solution, methotrexate (MTX) reacted with thallium(III) to form a 3:1 chelate. This resulted in great enhancement of second-order scattering (SOS) spectra and frequency doubling scattering (FDS) spectra and appearance of new SOS and FDS spectra. Their maximum wavelengths were located at 520 and 390 nm, respectively. The increments of scattering intensities (,I) were directly proportional to the concentrations of MTX in the ranges of 0.022,2.0 µg·mL,1 (SOS method) and 0.008,2.5 µg·mL,1 (FDS method). The methods exhibited high sensitivities. The detection limits for MTX were 7.4 ng·mL,1 (SOS method) and 2.3 ng·mL,1 (FDS method), respectively. The optimum conditions of the reaction, the influencing factors and the effects of coexisting substances were investigated. A highly sensitive, simple and fast method for the determination of MTX has been developed. The method can be applied satisfactorily to the determination of MTX in human serum samples. In this work, the charge distribution of MTX was calculated by a CNDO quantum chemistry method. In addition, the reaction mechanism was discussed. [source]

Theoretical Studies on Proton Transfer Reactions of 8-Hydroxyquinoline Monomers and Dimers

CHINESE JOURNAL OF CHEMISTRY, Issue 6 2006
Ji-Yang Zhao
Abstract Density functional theory (DFT) of quantum chemistry method was employed to investigate proton transfer reactions of 8-hydroxyquinoline (8-HQ) monomers and dimers. By studying the potential energy curves of the isomerization, the most possible reaction pathway was found. The total energy of 8-hydroxyquinoline was lower than that of quinolin-8(1H)-one, whereas the order was reversed in dimers. The findings explained the contrary experimental phenomena. The minimum reaction barrier of intramolecular proton transfer was 47.3 kJ/mol while that in dimer was only 25.7 kJ/mol. Hence it is obvious that proton transfer reactions of 8-HQ monomer have a considerable rate but it is easier to proceed for 8-HQ dimer than monomers. It implied that the hydrogen bond played an important role in depressing the activation energy of reaction. The mechanism of the tautomerization was discussed on the basis of theoretical results. [source]