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This paper describes the preparation of Pt- or W-supported Pt nanowires by directly growing them on the surface of Pt or W gauze. The growth direction of the nanowires was determined to be along the <111> axis. Electrochemical measurements were performed to investigate their catalytic performance toward methanol oxidation. It was found from cyclic voltammetry that the Pt nanowires supported on Pt gauze had the largest electrochemically active surface area with the greatest activity toward methanol oxidation reaction. They also exhibited a slightly slower current decay over time, indicating a higher tolerance to CO-like intermediates. Furthermore, electrochemical impedance spectroscopy measurements showed that the catalytic performance of the supported Pt nanowires prepared with a H(2)PtCl(6) precursor concentration of 40 mM is significantly better for methanol oxidation than the samples prepared at a concentration of 80 mM. This was due partially to the incomplete removal of poly(vinyl pyrrolidone) (PVP) from the more concentrated sample. In contrast, the Pt nanowires supported on W gauze performed the worst.
ACS Nano 2008 Oct 28
PMID:Electrocatalytic properties of Pt nanowires supported on Pt and W gauzes. 1920 64

A facile route was developed to create surface porous polystyrene/poly(vinylpyrrolidone) (PS/PVP) films, via phase separation in a dip-coating process, for antireflection applications. The film thickness, pore size, and pore depth of the product films can be effectively adjusted with the concentration of the PS/PVP (volume ratio of 7:3) solution and withdrawal speed. At an optimal concentration of 0.6 wt % and withdrawal speed of 19 cm/min, the product films had an average thickness of 125 nm, a pore size of 156 nm, and a pore depth of 20 nm, giving a percent transmittance increase of 3-4% over the bare glass. Further removal of the PVP phase, which was concentrated at the pore bottom, with water etching deepened the pore depth to 37 nm, thus boosting the percent transmittance for another 0.5%.
ACS Appl Mater Interfaces 2009 Jan
PMID:A facile route to create surface porous polymer films via phase separation for antireflection applications. 2035 56

This article describes a novel and simple route to preparing VO(2) thermochromic films by using a VOCl(2) solution with poly(vinylpyrrolidone) (PVP). X-ray diffraction and Raman spectra showed that the VO(2) films deposited with PVP consisted of a nearly pure monoclinic/rutile (M/R) phase. Conversely, films prepared without PVP contained obviously impure crystalline phases. The as-prepared films with PVP showed excellent optical properties compared to those prepared by common gas-phase methods: an integral visible transmittance of 54.5% and an IR reduction (change in transmittance) of 41.5% at 2000 nm. The phase-transition temperatures were adjusted from 69 to 54 degrees C by tungsten doping. Equipment analyses revealed that PVP plays two roles in the film formation. First, it fundamentally acts as a film-forming promoter to improve physical gelation via interactions among oppositely charged carbonyl groups and amine groups of the polymer. Second, the negatively charged carbonyl groups can interact with VO(2+) to form a uniform mixed-gel film after solvent evaporation. Thus, the addition of PVP can stabilize the solution and improve the as-prepared film quality and phase purity. The current study suggests that the process has promise in applications of smart windows.
ACS Appl Mater Interfaces 2009 Oct
PMID:A novel solution process for the synthesis of VO2 thin films with excellent thermochromic properties. 2035 55

Networks of nano/microfibers (fiber mats) have been electrospun from solutions of dispersed poly(vinylpyrrolidone) (PVP) and a titania precursor onto glass and indium-tin oxide (ITO) plates to study their wettability. Collection time and electrode separation are the two key fabrication parameters investigated, along with the flow rate, polymer molecular weight, and drying conditions, to determine the effects on network morphology and the relationship to contact angles. Measurements indicate that the fiber mats on both glass and ITO increase in thickness and contact angle for longer spinning time and shorter distance, resulting in an extreme case of apparent ultrahydrophobicity on ITO of up to 169.9 degrees with water. The fiber mats are shown by optical microscopy to exhibit differences in morphology for insulating glass (straight) and conductive ITO (loopy) substrates responsible for the wide-ranging and well-controlled wettability to within 1-2 degrees. Fiber mats baked at 200 degrees C for 24 h show excellent mechanical stability with wetting even against frequent heavy rinsing, conducive for reusable aqueous applications such as biosensors or cellular scaffolding.
ACS Appl Mater Interfaces 2009 Oct
PMID:Wettability of electrospun poly(vinylpyrrolidone)-titania fiber mats on glass and ITO substrates in aqueous media. 2035 69

We report herein a simple procedure for the fabrication of TiO2 nanofibers by the combination of electrospinning and sol-gel techniques by using poly(vinylpyrrolidone) (PVP), titanium(IV) butoxide, and acetylacetone in methanol as a spinning solution. TiO2 nanofibers (260-355 nm in diameter), with a bundle of nanofibrils (20-25 nm in diameters) aligned in the fiber direction, or particle-linked structures were obtained from the calcination of as-spun TiO2/PVP composite fibers at temperatures ranging from 300 to 700 degrees C. These nanofibers were utilized as photocatalysts for hydrogen evolution. The nanofiber photocatalyst calcined at 450 degrees C showed the highest activity among the TiO2 nanofibers tested such as ones prepared by the hydrothermal method and anatase nanoparticles (Ishihara ST-01). These results indicate that one-dimensional electrospun nanofibers with highly aligned bundled nanofibrils are beneficial for enhancement of the crystallinity, large surface area, and higher photocatalytic activity.
ACS Appl Mater Interfaces 2009 May
PMID:Photocatalytic activity for hydrogen evolution of electrospun TiO2 nanofibers. 2035 2

The adhesive joint between silica nanoparticles and ultrathin poly(vinylpyridine) (PVP) layers (thickness between 3 and 100 nm) was tested using the cantilever of an atomic force microscope. Specifically, the strength of the adhesive bond (or practical adhesion) was probed in a tearing contact mode, when the particle was removed by applying a tangential force parallel to the substrate surface. The effect of the polymer molecular weight and layer thickness on the particle (practical) adhesion was investigated. It was found that the particles were removed by destroying the cohesive contact zone and that the PVP layer thickness had a pronounced effect on the force needed to destroy the adhesive joint. In particular, the greater the layer thickness, the larger was the required break force. However, the strength of the adhesive joint was estimated to be higher for a thinner layer. It is suggested that mechanical properties of the system as well as molecular characteristics of the PVP layer are responsible for the trend observed. The molecular weight of the polymer did not significantly affect the strength of the adhesive bond.
ACS Appl Mater Interfaces 2009 Mar
PMID:Gluing nanoparticles with a polymer bonding layer: the strength of an adhesive bond. 2035 78

The morphological changes from tubules to large hollow spheres to (micelle-sized) small hollow-spherical silica were realized by polystyrene-block-poly(vinylpyridine) (PS-b-PVP) block copolymer micelle templates by controlling the intermolecular interactions with the corona chains. PS-b-PVP with weak intermolecular interactions among PVP corona chains yields the coexistence of tubules, large hollow spheres, and small hollow spheres. The coexistence of the three phases arises from the direct aggregation of block copolymer micelles during hydrolytic condensation of a silica precursor (tetraethylorthosilicate), as evidenced by transmission electron microscopy. When the degree of intermolecular interactions within the PVP corona blocks is increased by a change in either the degree of quaternization of the PVP blocks or the dielectric constant of the medium, small hollow spherical silica, with size equivalent to the block copolymer micelles, were solely obtained. We believe that this morphological change is due to the fact that the dipole-dipole interactions among quaternized PVP blocks physically cross-link the PVP coronas in micelles resisting the curvature change during the silica condensation.
ACS Appl Mater Interfaces 2009 Apr
PMID:Morphological changes from silica tubules to hollow spheres controlled by the intermolecular interactions within block copolymer micelle templates. 2035 17

Monodispersed SiO(2)-shell/ZnO-core composite nanospheres have been prepared in an oil-in-water microemulsion system. By using cyclohexane as the oil phase and Triton X-100 as the surfactant, composite nanospheres with high core loading levels and tunable shell thickness were obtained. Utilization of PVP capping agent on ZnO allowed the synthesis of composite nanospheres without forming any coreless SiO(2) spheres or shell-less ZnO particles. The photoactivity of ZnO nanoparticles was greatly reduced by SiO(2)-coating, which enables their applications as durable, safe, and nonreactive UV blockers in plastics, coating, and other products.
ACS Appl Mater Interfaces 2010 Apr
PMID:Reverse microemulsion-mediated synthesis of SiO(2)-coated ZnO composite nanoparticles: multiple cores with tunable shell thickness. 2042 16

Protein repellent coatings are widely applied to biomedical devices in order to reduce the nonspecific adhesion of plasma proteins, which can lead to failure of the device. Poly(N-vinylpyrrolidone) (PNVP) is a neutral, hydrophilic polymer with outstanding antifouling properties often used in these applications. In this paper, we characterize for the first time a cross-linking mechanism that spontaneously occurs in PNVP films upon thermal annealing. The degree of cross-linking of PNVP films and their solubility in water can be tailored by controlling the annealing, with no need for additional chemical treatment or irradiation. The physicochemical properties of the cross-linked films were investigated by X-ray photoelectron spectroscopy, infrared spectroscopy, neutron and X-ray reflectometry, ellipsometry, and atomic force microscopy, and a mechanism for the thermally induced cross-linking based on radical formation was proposed. The treated films are insoluble in water and robust upon immersion in harsh acid environment, and maintain the excellent protein-repellent properties of unmodified PNVP, as demonstrated by testing fibrinogen and immunoglobulin G adsorption with a quartz crystal microbalance. Thermal cross-linking of PNVP films could be exploited in a wide range of biotechnological applications to give antifouling properties to objects of any size, essentially making this an alternative to high-tech surface modification techniques.
ACS Appl Mater Interfaces 2010 Aug
PMID:Thermally cross-linked PNVP films as antifouling coatings for biomedical applications. 2073 14

Layered polymer/nanoparticle composites have been created through the one-step two-beam interference lithographic exposure of a dispersion of 25 and 50 nm silica particles within a photopolymerizable mixture at a wavelength of 532 nm. The polymerizable mixture is composed of pentaerythritol triacrylate (monomer), 1-vinyl-2-pyrrolidinone (monomer), and photoinitiator. In the areas of constructive interference, the monomer begins to polymerize via a free-radical process and concurrently the nanoparticles move into the regions of destructive interference. The effects of exposure time, power density, nanoparticle size, and periodicity on the final nanocomposite structure were measured with transmission electron microscopy to determine the mechanism for particle segregation. Diffraction from the sample was monitored as well, though its magnitude was not a good predictor of nanostructure in this relatively low index contrast system. Exposure time did not have a strong effect on the final structure. The best nanoparticle sequestration was observed at reduced laser power density, smaller interferogram periodicity, and decreased nanoparticle size, indicating that particle segregation is dominated by diffusion-limited nanoparticle transport directed by a matrix containing a gradient of polymerization kinetics.
ACS Nano 2010 Oct 26
PMID:Holographically directed assembly of polymer nanocomposites. 2092 38


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