2010 Vol. 23, No. 2

Article
A combination of high-field asymmetric waveform ion mobility spectrometry (FAIMS) with mass spectrometer (MS) was analyzed. FAIMS separates ions from the volatile organic compounds in the gas-phase as an ion-filter for MS. The sample ions were created at ambient pressure by ion source, which was equipped with a 10.6 eV UV discharge lamp (λ=116.5 nm).The drift tube of FAIMS is composed of two parallel planar electrodes and the dimension is 10 mm×8 mm×0.5 mm. FAIMS was investigated when driven by the high-filed rectangular asymmetric waveform with the peak-to-peak voltage of 1.36 kV at the frequency of 1 MHz and the duty cycle of 30%. The acetone, the butanone, and their mixture were adopted to characterize the FAIMS-MS. The mass spectra obtained from MS illustrate that there are ion-molecular reactions between the ions and the sample neutral molecular. And the proton transfer behavior in the mixture of the acetone and the butanone is also observed.With the compensation voltage tuned from -30 V to 10 V with a step size of 0.1 V, the ion pre-separation before MS is realized.
The reactions of anionic zirconium oxide clusters ZrxOy- with C2H6 and C4H10 are investi-gated by a time of flight mass spectrometer coupled with a laser vaporization cluster source.Hydrogen containing products Zr2O5H- and Zr3O7H- are observed after the reaction. Den-sity functional theory calculations indicate that the hydrogen abstraction is favorable in the reaction of Zr2O5- with C2H6, which supports that the observed Zr2O5H- and Zr3O7H- are due to hydrogen atom abstraction from the alkane molecules. This work shows a newpossible pathway in the reaction of zirconium oxide cluster anions with alkane molecules.
The production cross-sections, intensity ratios, and radiative Auger intensity ratios of Co, Ni, Cu, and Zn elements in different complexes were measured. The chemical effects on the K shell fluorescence parameters and the radiative Auger intensity ratios of these elements were investigated and the changes in these parameters were interpreted according to the charge transfer process. The samples were excited by 59.5 keV γ-rays from a 241Am annular radioactive source. K X-rays emitted by samples were counted by an Ultra-LEGe detector with a resolution of 150 eV at 5.9 keV.
A series of “H-shaped” organic dimers (azobenzene derivatives) exhibit linear absorption red shift compared with their corresponding monomers experimentally. Dipolar interaction model is not appropriate for the azobenzene derivatives due to the small distance between two “D-π-A” chains. Energy transfer model is suggested for explanation of the absorption red shift. Two necessary conditions for energy transfer were verified. In addition, bi-exponential florescence-delay behavior of the dimer as well as Bella's quantum chemistry calculation shows evidence of energy transfer.
Quasiclassical trajectory calculation of the title reaction O(3P)+H2→OH+H at three different scattering energies of 0.5, 0.75, and 1.0 eV on the lowest electronic potential energy surface 13A" has been done. Distribution P(θr) of polar angles between the relative velocityk of the reactant and rotational angular momentum vector j' of the product, distribution P(φr) of the azimuthal as well as dihedral angles correlating k-k'-j', 3-dimensional distri-bution, and polarization-dependent differential cross sections (PDDCSs)dependent upon the scattering angle of the product molecule OH between the relative velocity k of the reactant and k' of the product at different scattering energies of 0.5, 0.75, and 1.0 eV are presented and discussed.
The potential energy curves of the ground state X2+g of the fluorine molecule have been ac-curately reconstructed employing the Ryderg-Klein-Rees (RKR) method extrapolated by a Hulburt and Hirschfeler potential function for longer internuclear distances. Solving the cor-responding radial one-dimensional Schr?dinger equation of nuclear motion yields 22 bound vibrational levels above v=0. The comparison of these theoretical levels with the experimen-tal data yields a mean absolute deviation of about 7.6 cm-1 over the 23 levels. The highest vibrational level energy obtained using this method is 13308.16 cm?1 and the relative de-viation compared with the experimental datum of 13408.49 cm-1 is only 0.74%. The value from our method is much closer and more accurate than the value obtained by the quantum mechanical ab initio method by Bytautas. The reported agreement of the vibrational levels and dissociation energy with experiment is contingent upon the potential energy curve of the F2 ground state.
Molecular dynamics simulations were carried out to study the internal energy and microstruc-ture of potassium dihydrogen phosphates (KDP) solution at different temperatures. The water molecule was treated as a simple-point-charge model, while a seven-site model for the dihydrogen phosphate ion was adopted. The internal energy functions and the radial dis-tribution functions of the solution were studied in detail. An unusually large local particle number density fluctuation was observed in the system at saturation temperature. It has been found that the specific heat of oversaturated solution is higher than that of unsaturated solution, which indicates the solution experiences a crystallization process below saturation temperature. The radial distribution function between the oxygen atom of water and the hydrogen atom of the dihydrogen phosphate ion shows a very strong hydrogen bond struc-ture. There are strong interactions between potassium cation and oxygen atom of dihydrogen phosphate ion in KDP solution, and much more ion pairs were formed in saturated solution.
The mechanism and regioselectivity of 1,3-dipolar cycloaddition of N-[methyl]-C-[5-nitro-2-furyl] nitrilimine with dimethyl 7-oxabicyclo[2,2,1]hepta-2,5-diene-2,3-dicarboxylate were investigated using activation energy calculations and density functional theory-based re-activity indexes. The reaction proceeds by an asynchronous concerted mechanism. The calculations are performed at the B3LYP/6-31G(d) level of theory and the obtained results are in agreement with experimental outcome.
The mechanism of the cycloaddition reaction between singlet dimethyl-silylene carbene and acetone has been investigated with density functional theory, From the potential energy profile, it can be predicted that the reaction has two competitive dominant reaction pathways. The presented rule of this reaction: the [2+2] cycloaddition effect between the πorbital of dimethyl-silylene carbene and the π orbital of π-bonded compounds leads to the formation of a twisty four-membered ring intermediate and a planar four-membered ring product; The unsaturated property of C atom from carbene in the planar four-membered ring product,resulting in the generation of CH3-transfer product and silicic bis-heterocyclic compound.
The process and mechanism of the ligand volume controlled Pd(PR3)2 (PR3=PH3, PMe3, and PtBu3) oxidative addition with aryl bromide were investigated, using density functional theory method with the conductor-like screening model. Association pathway and dissocia-tion pathway were investigated by the comparison of several energies. The cleavage energy of Pd(PR3)2 complex was calculated, as well as the oxidative addition reaction barrier energy of Pd(PR3)n (n=1,2) with aryl bromide in N,N-dimethylformamide solvent. This study proved that the ligands volume possessed a great impact on the mechanism of oxidative addition: less bulky ligand palladium associated with aryl bromide via two donor ligands,but larger bulky ligand palladium coordinated via monoligand.
The thermodynamic properties of linear protein solutions are discussed by a statistical me-chanics theory with a lattice model. The numerical results show that the Gibbs function of the solution decreases, and the protein chemical potential is enhanced with increase of the protein concentration for dilute solutions. The influences of chain length and temperature on the Gibbs function of the solution as well as the protein chemical potential are analyzed.As an application of the theory, the chemical potentials of some mutants of type I antifreeze proteins are computed and discussed.
Three kinds of polymeric materials are taken as example for the verification of linear ex-trapolation method from unified master lines with reduced universal equations on creep and stress relaxation tests. The theoretical values of long-term mechanical behavior and lifetime for a cured epoxide, polypropylene, poly(methyl-methacrylate), and SBR rubber are directly evaluated with the universal equations on reduced creep compliance and reduced stress relax-ation modulus and are compared with their predicted values by the linear extrapolation from the unified master lines of creep and stress relaxation. The results show that the theoretical values of dimensional stability, bearing ability and lifetime are in an excellent agreement with the predicted values, it shows that the linear extrapolation method is more simple and reliable. The dependences of long-term mechanical behaviors and lifetime on the different aging times are discussed.
A new bovine serum albumin (BSA) surface imprinting method was developed by the in-corporation of quantum dots (QDs) into molecularly imprinted polymers (MIP), which can offer shape selectivity. Preparation and adsorption conditions were optimized. Physical ap-pearance of the QDs and QDs-MIP particles was illustrated by scanning electron microscope images. Photoluminescence emission of CdS was quenched when rebinding of the template.The quenching of photoluminescence emissions is presumably due to the fluorescence reso-nance energy transfer between quantum dots and BSA template molecules. The adsorption is compiled with Langmuir isotherm, and chemical adsorption is the rate-controlling step.The maximum adsorption capacity could reach 226.0 mg/g, which is 142.4 mg/g larger than that of undoped BSA MIP. This study demonstrates the validity of QDs coupled with MIP technology for analyzing BSA.
The energetics, electronic structures, and optical properties of several neutral vacancies for γ-Si3N4 are studied based on density function theory within the generalized gradient approximation. The binding and formation energies of nitrogen vacancy are smaller than that of silicon vacancies, implying that nitrogen vacancy can be easily formed in γ-Si3N4.Corresponding density of states of different point vacancies is analyzed. We concluded that the neutral silicon vacancies introduce the p-type carriers into the system, whereas single nitrogen vacancy leads to an n-type semiconductor. The results show indirect semiconductor of nitrogen vacancy for γ-Si3N4. The effects of optical properties are discussed on single vacancies for γ-Si3N4. For silicon vacancies, the materials have much higher static dielectric constants than these of nitrogen vacancy and perfect γ-Si3N4. The single nitrogen vacancy for γ-Si3N4 has no effects on absorption and reflection in visible and infrared light. For silicon vacancy, it is significantly increased.
Polypyrrole (PPY) microbelts are synthesized via the absorbent cotton template for the first time. PPY microbelts are characterized by Fourier transform infrared spectroscopy.The stability, the morphology and electrical conductivity of such microbelts are evaluated by means of scanning electron microscope, thermo-gravimetric analysis and four-probe con-ductivity. A possible mechanism for the formation of PPY microbelts are proposed. The conductivity is measured, and the conductivity variation mechanism of the PPY microbelts with the pyrrole monomer concentrations is analyzed.
The electrochemical deposition technique was applied to achieve porous silicon (PS) surface passivated with Ag deposition for improving the properties of PS photoluminescence. The relation of Ag depositing forms to current density and the effect of PS hydrophilic surface on deposition uniformity were investigated. The experimental results indicated that there were two critical current densities (maximum and minimum) in which Ag was absent and electroplated on PS surface correspondingly, and the range of current density for deposition of Ag on porous silicon was from 50 μA/cm2 to 400 μA/cm2. The process of changing PS surface from hydrophobic into hydrophilic had positive effect on Ag deposition uniformity. Under the same experimental conditions, PS hydrophobic surface presented uneven Ag deposition.However, hydrophilic surface treated with SC-1 solution was even. Finally, the effect of PS surface passivation with Ag even deposition on photoluminescence intensity and stabilization of PS was studied. It was discovered that Ag passivation inhibited the degradation of PL intensity effectively. In addition, excessive Ag deposition had a quenching effect on room-temperature visible photoluminescence of PS.
The efficient thickness of a composite electrode for solid oxide fuel cells was directly calcu-lated by developing a physical model taking into account of the charge transfer process, the oxygen ion and electron transportation, and the microstructure characteristics of the elec-trode. The efficient thickness, which is defined as the electrode thickness corresponding to the minimum electrode polarization resistance, is formulated as a function of charge trans-fer resistivity, effective resistivity to ion and electron transport, and three-phase boundary length per unit volume. The model prediction is compared with the experimental reports to check the validity. Simulation is performed to show the effect of microstructure, intrinsic material properties, and electrode reaction mechanism on the efficient thickness. The results suggest that when an electrode is fabricated, its thickness should be controlled regarding its composition, particle size of its components, the intrinsic ionic and electronic conductivities,and its reaction mechanisms as well as the expected operation temperatures. The sensitivity of electrode polarization resistance to its thickness is also discussed.
Fatigue properties of magnetorheological elastomer (MRE) samples were investigated based on cis-polybutadiene rubber by using a fatigue test machine. Three MRE samples with iron particles mass fraction of 60%, 70%, and 80% were fabricated, and their properties dependence of three strain amplitudes (50%, 75%, and 100%) were measured. The absolute magnetorheological (MR) effect, storage modulus, and loss modulus of MRE samples after fatigue were evaluated by a modified dynamic mechanical analyzer. The results revealed that MR effect, storage modulus, and loss modulus of MREs containing 80% iron particles depended strongly on the strain amplitudes and the number of cycles, while storage mod-ulus and loss modulus of MREs containing 70% iron particles also depended on the strain amplitudes and the number of cycles but not as strongly as sample which contains 80% iron particles, but the properties of MREs containing 60% iron particles after cyclic deforma-tion were almost independent of the fatigued conditions. In order to investigate the fatigue mechanism of MREs, the sample was carried out with a quasi-static tensile testing and its surface morphology during testing was observed in situ by scanning electron microscopy.
Self-made TiO2 nanoparticles were used as photoelectrode material of dye sensitized solar cell. The TiO2 thin film coats through spreading nanoparticles evenly onto the ITO glass via self-made spin-heat platform, and then TiO2 thin film is soaked in the dye N-719 more than 12 h to prepare the photoelectrode device. The TiO2 nanoparticles produced by electric-discharge-nanofluid-process have premium anatase crystal property, and its diameter can be controlled within a range of 20-50 nm. The surface energy zeta potential of nanofluid is from -22 mV to -28.8 mV, it is a stable particle suspension in the deionized water. A trace of surfactant Triton X-100 put upon the surface of ITO glass can produce a uniform and dense TiO2 thin film and heating up the spin platform to 200 oC is able to eliminate mixed surfac-tant. Self-made TiO2 film presents excellent dye absorption performance and even doesn't need heat treatment procedure to enhance essential property. Results of energy analysis show the thicker film structure will increase the short-circuit current density that causes higher conversion efficiency. But, as the film structure is large and thick, both the open-circuit voltage and fill factor will decline gradually to lead bad efficiency of dye-sensitized solar cell.
At 105 K, strontium titanate is known to undergo an antiferrodistortive transition transform-ing from cubic to tetragonal structure as a result of the rotation of the oxygen octahedral around a cubic axe. Based on the Curie principle, the order parameter is determined to be a third-order complete symmetry polarization tensor. To take into account of quantum effects,the dielectric permittivity is measured from Landau free energy, and the Curie Weiss-type behavior is analyzed. From crystallization chemistry viewpoint, the dielectric behavior at low temperature is connected to small radius of Sr2+, which is much easier to move around the oxygen octahedral than Ba2+ in BaTiO3 or Pb2+ in PbTiO3.
A dielectric analysis model for the fouling layer on the polyethersulfone composite ultrafil-tration (UF) membrane and solution system, which consists of the solution, concentration polarization layer (CPL), and cake layer, was established by virtue of the interfacial polar-ization and the electrostatic field theory. The effect of some important parameters, such as the depth, conductivity of CPL, and cake layer, on the dielectric spectroscopy (or dielectric relaxation properties) of the UF system was discussed by the parameter sensitivity analy-sis and the dielectric measurement. The simulations indicate that the CPL can be created rapidly and the cake layer formation is the dynamic balance process of growth and erosion in the process of UF. The key factor affecting on the dielectric spectrum of UF system is the electrical properties of the CPL and the cake layer. In comparison to the results of dielectric measurement, the simulations indicate that the model proposed in this work is valid and reliable to some degree for describing and explaining the dielectric relaxation phenomenon in UF system. It is very important to further understand the fouling behavior of membrane surface and optimize the controlling techniques of membrane fouling in the process of UF.