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排序方式: 共有1153条查询结果,搜索用时 34 毫秒
171.
The adsorption characteristics of 1,3‐benzenedithiol (1,3‐BDT) and 1,3‐benzenedimethanethiol (1,3‐BDMT) on Au surfaces are investigated by means of surface‐enhanced Raman scattering, UV/Vis absorption spectroscopy, and cyclic voltammetry (CV). 1,3‐BDMT is found to adsorb via two S–Au linkages at concentrations below monolayer coverage, but to have an upright geometry as the concentration increases on Au nanoparticles. On the other hand, 1,3‐BDT is found to adsorb by forming two S–Au linkages, regardless of concentration, based on the disappearance of the ν(SH)free stretching band. Because of the absence of the methylene unit, 1,3‐BDT appeares not to self‐assemble efficiently on Au surfaces. The UV/Vis absorption spectroscopy and CV techniques are also applied to check the formation of self‐assembled monolayers of 1,3‐BDT and 1,3‐BDMT on Au. Density functional theory calculations based on a simple adsorption model using an Au8 cluster are performed to better understand the nature of the adsorption characteristics of 1,3‐BDT and 1,3‐BDMT on Au surfaces. 相似文献
172.
Joo JE Pham VT Tian YS Chung YS Oh CY Lee KY Ham WH 《Organic & biomolecular chemistry》2008,6(8):1498-1501
A concise, stereocontrolled synthesis of (+)-polyoxamic acid was achieved. Starting from trans-oxazoline as a chiral building block, the key step involves diastereoselective oxazine formation catalyzed by palladium(0). 相似文献
173.
Dong Joo Moon Seoung Dal Jung 《Journal of Mathematical Analysis and Applications》2008,342(1):354-360
Let M be a complete Riemannian manifold and let N be a Riemannian manifold of non-positive sectional curvature. Assume that at all x∈M and at some point x0∈M, where μ0>0 is the least eigenvalue of the Laplacian acting on L2-functions on M. Let 2?q?p. Then any q-harmonic map of finite q-energy is constant. Moreover, if N is a Riemannian manifold of non-positive scalar curvature, then any q-harmonic morphism of finite q-energy is constant. 相似文献
174.
175.
Park MS Lim TH Jeon YM Kim JG Joo SW Gong MS 《Journal of colloid and interface science》2008,321(1):60-66
We developed a simple method for the preparation of polyelectrolyte/silver nanocomposites, where silver nanoparticles were dispersed in a polyelectrolyte. Copoly(TEAMPS/VP)/silver (w/w=100/0, 100/1, 100/2, 100/3 and 100/4) nanocomposites were obtained by a thermal decomposition reaction of silver carbamate complex at 130 degrees C, and well-dispersed silver colloids were stabilized by copolymer of tetraethylammonium 2-acrylamido-2-methyl-1-propanesulfonate (TEAMPS) and N-vinylpyrrolidone (VP). A dark brown solution in its UV-vis absorption spectrum showed surface plasmon resonance absorption bands at 420 nm in solution. The silver precursor and the resulting polyelectrolyte/Ag nanocomposite was characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray diffraction (XRD), infrared (IR), transmission electron microscopy (TEM). In addition the humidity-sensing properties using copoly(TEAMPS/VP)/Ag nanocomposite films were examined. 相似文献
176.
177.
Graft copolymers comprising poly(vinylidene fluoride‐co‐chlorotrifluoroethylene) backbone and poly(styrene sulfonic acid) side chains, i.e. P(VDF‐co‐CTFE)‐g‐PSSA were synthesized using atom transfer radical polymerization (ATRP) for composite nanofiltration (NF) membranes. Direct initiation of the secondary chlorinated site of CTFE units facilitates grafting of PSSA, as revealed by FT‐IR spectroscopy. The successful “grafting from” method and the microphase‐separated structure of the graft copolymer were confirmed by transmission electron microscopy (TEM). Wide angle X‐ray scattering (WAXS) also showed the decrease in the crystallinity of P(VDF‐co‐CTFE) upon graft copolymerization. Composite NF membranes were prepared from P(VDF‐co‐CTFE)‐g‐PSSA as a top layer coated onto P(VDF‐co‐CTFE) ultrafiltration support membrane. Both the rejections and the flux of composite membranes increased with increasing PSSA concentration due to the increase in SO3H groups and membrane hydrophilicity, as supported by contact angle measurement. The rejections of NF membranes containing 47 wt% of PSSA were 83% for Na2SO4 and 28% for NaCl, and the solution flux were 18 and 32 L/m2 hr, respectively, at 0.3 MPa pressure. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
178.
Qian S Joo SW Hou WS Zhao X 《Langmuir : the ACS journal of surfaces and colloids》2008,24(10):5332-5340
The electrophoretic motion of a spherical nanoparticle, subject to an axial electric field in a nanotube filled with an electrolyte solution, has been investigated using a continuum theory, which consists of the Nernst-Planck equations for the ionic concentrations, the Poisson equation for the electric potential in the solution, and the Stokes equation for the hydrodynamic field. In particular, the effects of nonuniform surface charge distributions around the nanoparticle on its axial electrophoretic motion are examined with changes in the bulk electrolyte concentration and the surface charge of the tube's wall. A particle with a nonuniform charge distribution is shown to induce a corresponding complex ionic concentration field, which in turn influences the electric field and the fluid motion surrounding the particle and thus its electrophoretic velocity. As a result, contrary to the relatively simple dynamics of a particle with a uniform surface charge, dominated by the irradiating electrostatic force, that with a nonuniform surface charge distribution shows various intriguing behaviors due to the additional interplay of the nonuniform electro-osmotic effects. 相似文献
179.
Joo W Yang SY Kim JK Jinnai H 《Langmuir : the ACS journal of surfaces and colloids》2008,24(21):12612-12617
Cylindrical nanoporous structures were prepared by using a mixture film of polystyrene-block-poly(methyl methacrylate) copolymer (PS-b-PMMA) and PMMA homopolymer (hPMMA), and they were analyzed by transmission electron microtomography (TEMT), X-ray reflectivity (XR), and grazing incidence small-angle X-ray scattering. For this purpose, the mixture film was spin-coated onto a silicon wafer modified by a neutral brush for PS and PMMA blocks, which generates PMMA cylindrical microdomains oriented normal to the substrate. Two methods were employed to prepare nanoporous structures: (1) all of the PMMA phase (PMMA block and PMMA homopolymer) in the film was removed by UV irradiation, followed by rinsing with a selective solvent (acetic acid) to PMMA and (2) only PMMA homopolymer was removed by selective solvent etching without UV irradiation. We found via TEMT and XR that the nanoporous structure in the film prepared by UV irradiation exhibited almost perfect cylindrical shape throughout the entire film thickness. However, when the film was rinsed with a selective solvent, nanoporous structures were not straight cylinders but had a funnel shape in which the diameter of nanopores located near the top of the film was larger than that located near the bottom of the film. 相似文献
180.
Baik JM Shon Y Lee SJ Jeong YH Kang TW Lee JL 《Journal of the American Chemical Society》2008,130(41):13522-13523
We report the room-temperature ferromagnetism in transition metals (Co, Ni)-doped 8-hydroxy-quinoline aluminum (Alq3) by thermal coevaporation of high purity metal and Alq3 powders. For 5% Co-doped Alq3, a maximum magnetization of approximately 0.33 microB/Co at 10 K was obtained and ferromagnetic behavior was observed up to 300 K. The Co atoms interact chemically with O atoms and provide electrons to Alq3, forming new states acting as electron trap sites. From this, it is suggested that ferromagnetism may be associated with the strong chemical interaction of Co atoms and Alq3 molecules. 相似文献