An approach for fabricating self-assembled monolayer of Ag nanoparticles on gold as the SERS-active substrate

In this paper, an approach for fabricating an active surface-enhanced Raman scattering (SERS) substrate is adopted. This approach is based on the assembling of silver nanoparticles film on gold substrate. Rhodamine 6G (R6G) and p-aminothiophenol (P-ATP) were used as probe molecules for SERS experiments, showing that this new active substrate has sensitivity to SERS response. Tapping-mode atomic force microscopy (AFM) was also used to investigate the surface morphology following the fabricating process of the active SERS substrate, which showed that large quantities of silver nanoparticles were uniformly coated on the substrate.

Structure-properties relationship in toughening of poly(butylene terephthalate) with core-shell modifier

The performance of acrylonitrile-butadiene-styrene (ABS) core-shell modifier with different grafting degree, acrylonitrile (AN) content, and core-shell ratio in toughening of poly(butylene terephthalate) (PBT) matrix was investigated. Results show PBT/ABS blends fracture in ductile mode when the grafting degree is high, and with the decrease of grafting degree PBT/ABS blends fracture in a brittle way. The surface of rubber particles cannot be covered perfectly for ABS with low grafting degree and agglomeration will take place; on the other hand, the entanglement density between SAN and PBT matrix decreases because of the low grafting degree, inducing poor interfacial adhesion. The compatibility between PBT and ABS results from the strong inter-action between PBT and SAN copolymer and the interaction is influenced by AN content. Results show ABS cannot disperse in PBT matrix uniformly when AN content is zero and PBT/ABS fractures in a brittle way. With the addition of AN in ABS, PBT/ABS blends fracture in ductile mode. The core-shell ratio of ABS copolymers has important effect on PBT/ABS blends.

Simple preparation method of Pd nanoparticles on an Au electrode and its catalysis for dioxygen reduction

A simple method for the fabrication of Pd nanoparticles is described. The three-dimensional Pd nanoparticle films are directly formed on a gold electrode surface by simple electrodeposition at -200 mV from a solution of 1 M H2SO4+0.01 mM K2PdCl4. X-Ray photoelectron spectroscopy verifies the constant composition of the Pd nanoparticle films. Atomic force microscopy proves that the as-prepared Pd nanoparticles are uniformly distributed with an average particle diameter of 45-60 nm. It is confirmed that the morphology of the Pd nanoparticle films are correlated with the electrodeposition time and the state of the Au substrate. The resulting Pd-nanoparticle-film-modified electrode possesses high catalytic activity for the reduction of dissolved oxygen in 0.1 M KCl solution. Freshly prepared Pd nanoparticles can catalyze the reduction of O-2 by a 4-electron process at -200 mV in 0.1 M KCl, but this system is not very stable. The cathodic peaks corresponding to the reduction of O-2 gradually decrease with potential cycling and at last reach a steady state. Then two well-defined reduction peaks are observed at -390 and -600 mV vs. Ag/AgCl/KCl (sat.). Those two peaks correspond to a 2-step process for the 4-electron reduction pathway of O-2 in this neutral medium.

Effects of surfactant loadings on the dispersion of clays in maleated polypropylene

A series of organically modified clays (OMCs) with a surfactant loading range from 0.625 to 2.5 times the cation exchange capacity (CEC) were melt-mixed with maleated polypropylene (PPMA). Wide-angle X-ray diffraction and transmission electron microscopy results of these narrocomposites show that dispersion of clays becomes unfavorable in the PPMA matrix during melt intercalation as the surfactant loading increases in the process of modifying clays, though larger interlayer distances are obtained in their corresponding OMCs. It is even important that clays uniformly disperse at the nanoscale level in the PPMA matrix when the surfactant loadings are below the CEC, which implies that incomplete exchange of inorganic cations in the process of modifying clay benefits the dispersion of clays in the PPMA matrix.

Characterization of organic-inorganic multilayer films by cyclic voltammetry, UV-Vis spectrometry, X-ray photoelectron spectroscopy, small-angle X-ray diffraction and electrochemical impedance spectroscopy

We have employed several techniques, including cyclic voltammetry, UV-Vis spectrometry, small-angle X-ray diffraction, X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy, to characterize the formation processes and interfacial features of ultrathin multilayer films of silicotungstate and a cationic redox polymer on cysteamine-coated Au electrodes self-assembled monolayers. All of these techniques confirm that the multilayer films are built up stepwise as well as uniformly in a layer-by-layer fashion. In particular, the electrochemical impedance spectroscopy is successfully used to monitor the multilayer deposition processes. It has been proved that the electrochemical impedance spectroscopy is a very useful technique in characterization of multilayer films because it provides valuable information about the interfacial impedance features.

Sol-gel preparation and luminescence properties of nano-structured hybrid materials incorporated with europium complexes

Microporous silica gel has been prepared by the sol-gel method utilizing the hydrolysis and polycondensation of tetraethylorthosilicate (TEOS). The gel has been doped with the luminescent ternary europium complex Eu(TTA)(3)(.)phen: where HTTA=1-(2-thenoyl)-3,3,3-trifluoracetone and phen=1,10-phenanthroline. By contrast to the weak f-f electron absorption bands of Eu3+, the complex organic ligand exhibits intense near ultraviolet absorption. Energy transfer from the ligand to Eu3+ enables the production of efficient, sharp visible luminescence from this material. Utilizing the polymerization of methyl methacrylate, the inorganic/polymer hybrid material containing Eu(TTA)(3)(.)phen has also been obtained. SEM micrographs show uniformly dispersed particles in the nanometre range. The characteristic luminescence spectral features of europium ions are present in the emission spectra of the hybrid material doped with Eu(TTA)(3)(.)phen.

Characterization of Y2O3 : Eu coated with polystyrene

The core-shell Y2O3:Eu3+/polystyrene particles was prepared by surface modification with citric acid and emulsion polymerization method of styrene. The DTA curve of coated particles exhibits a small and wide exothermic peak of organic compound around 387 degreesC. The carbonyl stretching vibration band was shifted to low wavenumber in FTIR spectrum and the binding energy of Y3d5/2 was shifted to high-energy band in XPS spectrum. The results of FTIR and XPS show that citric acid was coupled to the particles surface. The hydrophilic surface became amphiphilic by modification of citric acid. So styrene could adsorb on particles surface to form emulsion structure which inorganic core was inside. EDS spectra show that Y2O3:Eu3+ particles were coated uniformly with polystyrene.

Oriented polyoxometalate-polycation multilayers on a carbon substrate

In this paper, a new method of fabricating multilayers on a carbon substrate is presented. First, a uniformly charged carbon surface was prepared through molecular design. Then an ultrathin film consisting of layer-pairs of oppositely charged polymeric cationic poly(diallyldimethylammonium chloride) (PDDA) and silicotungstate, SiW12O404- (SiW12), was grown layer-by-layer onto the grafted carbon substrate using a molecular self-assembly technique and an electrochemical method. The technique allows one to prepare highly adherent, dense and smooth films of polyoxometalates with special properties. By combining cyclic voltammetry (CV) and X-ray (XR) reflectometry, it was determined that the average surface density of SiW12 was 2.10 x 10(-10) mol cm(-2), and the thickness increase per adsorption of PDDA-SiW12 was 1.7 +/- 0.2 nm, indicating that the amount of SiW12 anion per one layer adsorption corresponded to a monolayer coverage. Atomic force microscopy (AFM) was also used to examine the surface morphology and determine the grain size distribution and roughness for multilayer films. An increase in root-mean-square (RMS) surface roughness from 7 to 9 Angstrom was observed as the number of layer-pairs in the film increased from 2 to 6. FTIR results showed that the good stability of the multilayer films was due to Coulomb interactions between the SiW12 anion and the polymeric cations PDDA. Moreover, the multilayer films, in acidic aqueous solution, showed good electrocatalytic activity toward the reduction of NO2-, and the catalytic currents increased with increasing the layer numbers of SiW12 adsorption. These characteristics of the multilayer films might find potential applications in the field of sensors and microelectronics devices.

Preparation and luminescence properties of sol-gel hybrid materials incorporated with europium complexes

Microporous silica gel has been prepared by the sol-gel method utilizing the hydrolysis and polycondensation of tetraethylorthosilicate (TEOS). The gel has been doped with the luminescent ternary europium complex Eu(TTA)(3). phen: where HTTA = 1-(2-thenoyl)-3,3,3-trifluoracetone and phen = 1,10-phenanthroline. By contrast to the weak f-f electron absorption bands of Eu3+, the complex organic ligand exhibits intense near ultraviolet absorption. Energy transfer from the ligand to Eu3+ enables the production of efficient, sharp visible luminescence from this material. Utilizing the polymerization of methyl methacrylate or ethyl methacrylate, the inorganic/polymer hybrid materials containing Eu(TTA)(3). phen have also been obtained. SEM micrographs show uniformly dispersed particles in the nanometre range. The characteristic luminescence spectral features of europium ions are present in the emission spectra of the hybrid material doped with Eu(TTA)3 phen. (C) 2000 Kluwer Academic Publishers.

Simple preparation method of multilayer polymer films containing Pd nanoparticles

A simple route to the fabrication of multilayer films containing Pd nanoparticles is described. Following layer-by-layer assembly of PdCl42- and polycation, QPVP-Os (a quaternized poly(4-vinylpyridine) complexed with [Os(bpy)(2)Cl](2+/+)), on 4-aminobenzoic acid-modified glassy carbon electrodes, the three-dimensional Pd nanoparticle multilayer films are directly formed on electrode surfaces via electrochemical reduction of PdCl42- sandwiched between polymers. The growth of PdCl42- is easy on electrode surfaces by electrostatic interaction, and the assembly processes are monitored by cyclic voltammetry and UV-vis spectroscopy. The depth profile analyses by X-ray photoelectron spectroscopy verify the constant composition of the Pd nanoparticle multilayer films. Atomic force microscopy proves that the as-prepared Pd nanoparticles are uniformly distributed with an average particle diameter of 3-7 mn. The resulting Pd nanoparticle multilayer-modified electrode possesses high catalytic activity for the reduction of dissolved oxygen and oxidation of hydrazine compounds in aqueous solution.

Sol-gel synthesis and properties of Ce1-xGdxO2-x/2 solid solutions

A series of solid electrolytes Ce1-xGdxO2-x/2(x=0 similar to0.6) was prepared by sol-gel method. The structure, thermal expansion coefficient and electrical properties of the solid solutions were systematically studied. XRD data showed that a complete cubic fluorite structure was formed at 160 degreesC. The purity of the product prepared by the sol-gel method is higher, the grain size is uniformly smaller. They were easily sintered into highly dense ceramic pellets at 1 300 degreesC. The sintering temperature was significantly lower than that by traditionally high temperature solid phase reaction method. The thermal expansion coefficient of Ce0.8Gd0.2O1.9, determined from high- temperature XRD data, is 8. 125 X 10(-6) K-1. Impedance spectra analyses showed that the grain-boundary resistance of the solid electrolyte prepared by sol-gel method was reduced or even eliminated. The conductivity of Ce0.8Gd0.2O1.9 is 5.26 X 10(-3) S/cm at 600 degreesC. The activation energy (E-a) is 0.82 eV.

Preparation of stable mesoporous silica FSM-16 from water glass in the presence of cetylpyridium bromide

The synthesis and characterization of the mesoporous materials FSM-16 (folded sheets mesoporous materials) with highly ordered structure in open-vessel by using cetylpyridium bromide (CPBr) and the single-layered polysilica Kanemite as new template and silicon source, respectively, has been investigated systematically. The hexagonal arrangements of uniformly size pores were characterized by FTIR. XRD. nitrogen adsorption. TG-DTA. SEM and TEM. Especially, the porous products with higher surface areas show remarkable thermal stability up to 1000 C. The potential application as carrier of catalysts or host-guest materials is anticipated. (C) 2001 Elsevier Science B.V. All rights reserved.

Ring-banded spherulite surface structure of poly(epsilon-caprolactone) in its miscible mixtures with poly(styrene-co-acrylonitrile)

The surface structure of the ring-banded spherulites in polymer blends PCL/SAN (90/10) was studied by optical microscopy, SEM, and TEM, respectively. It is interesting to find that the surface structure of the ring-banded spherulites in polymer blends PCL/SAN (90/10) is made up of the convex bands. The landscape of the convex bands on the surface has been little emphasized before. Radial fibrils are arranged on the bands. Details of the radial fibrils on the bands can be observed by TEM. The landscape of the convex bands on the surface and twisting of lamellae in the convex bands for PCL/SAN blends may be useful to explain the formation mechanism of the ring banded spherulites in polymer blends or even in homopolymers. (C) 1999 John Wiley & Sons, Inc.

Fabrication and characterization of heteropolyanion Langmuir-Blodgett films

The possibility of the formation of Langmuir-Blodgett (LB) films with dimethyldioctadecylammonium (DODA) after the addition of cobalt(II)-substituted Dawson-type tungstodiphosphate anion (briefed as (H2O)(CoP2W17O618-)-P-11) in the subphase has been explored. Marked modifications of the compression isotherms are observed when this anion is dissolved in the subphase, which demonstrates that the polyanions interact with the monolayers. LB films have been readily obtained from this system. The adsorption Fourier transform IR (FT IR) spectroscopy, atomic force microscopy (AFM), X-ray diffraction (XRD) and cyclic voltammetry (CV) have been used to investigate the morphological and molecular structure of the deposited film. The FT IR results showed the presence of the polyanion within the LB films, and the shift for its characteristic bands may be related to the presence of positively charged DODA. AFM measurement reveals that the LB films of DODA/(H2O)(CoP2W17O618)-P-II are regularly and uniformly deposited on the substrate. XRD experiments prove that the lamellar structure of the LB films of DODA/(H2O)(CoP2W17O618-)-P-II is well-defined. The LB films of DODA/(H2O)(CoP2W17O618-)-P-II immobilized onto an indium-oxide (ITO) glass, in aqueous solutions of pH 2.0-5.0, show quite facile redox reactions even for multilayers. All the experiments carried out in the present study suggest that the new materials of heteropolyanions can be formed by LB techniques and beneficial physicochemical properties of heteropolyanions can be maintained/enhanced through molecular-level design. (C) 1999 Elsevier Science S.A. All rights reserved.

Study on the self-packing of SnO2 nanoparticles at the air-hydrosol interface and its composite LB films with arachidic acid

SnO2 nanoparticles were found to self-pack at the air-hydrosol interface and form a nanoparticulate film. The self-packed films were observed under a Brewster angle microscope, and investigated by recording the time evolution of surface pressure and pi-A isotherms. The results show that SnO2 nanoparticles take 3 h to form a complete film at the air-hydrosol interface. Composite monolayers of SnO2 and arachidic acid were obtained by spreading arachidic acid onto a fresh hydrosol surface. Composite Y-type LB films were transferred from the air-hydrosol interface onto substrates, and characterized by FTIR, UV-vis, X-ray diffraction spectroscopy and TEM techniques. The results show that the composite films have good structure, with SnO2 nanoparticles uniformly and compactly distributed in the arachidate matrix. (C) 1998 Elsevier Science S.A. All rights reserved.