Showing papers by "Ramón Tena-Zaera published in 2009"

Multiresponsive PEDOT–Ionic Liquid Materials for the Design of Surfaces with Switchable Wettability

Abstract: Among the different types of stimuli-responsive polymers, conjugated polymers reveal unique multiresponsive behavior. In this work, the synthesis and characterization of new functional poly(3,4-ethylenedioxythiophenes) (PEDOT) bearing imidazolium ionic-liquid moieties (PEDOT-Im) is reported. PEDOT-Im polymers show multiresponsive properties to a variety of stimuli, such as temperature, pH, oxidative doping, and presence of anions. These stimuli provoke different changes in PEDOT-Im, such as changes in color, oxidation state, and, wetting behavior. In all cases, a reversible effect is observed, and the polymers reveal responsive properties in solution as well as in the form of thin films. Whereas sensitiveness to pH and oxidative doping are known phenomena for other PEDOT derivatives, responsiveness to temperature and to anions is a unique property of PEDOT-Im. The anion exchange is further investigated by means of the Quartz Crystal Microbalance with dissipation. Anion exchanges induce fast, adjustable, and reversible contact angle changes between 24° and 107°. As a potential application, surfaces with switchable wettability triggered by anion solutions are prepared by spin-coating PEDOT-Im films onto different substrates.

Localized versus delocalized states: Photoluminescence from electrochemically synthesized ZnO nanowires

Abstract: 810 19 cm 3 in the as-deposited nanowires and show that the near-band-edge emission results from band-to-band recombination processes delocalized states. A photoluminescence band centered at 3.328 eV scales with the diameter of the nanowires and is assigned to recombination processes involving surface states. We show that annealing at 500 °C in air reduces the donor density in the nanowires by more than one order of magnitude, leading to sharp excitonic transitions in the electrochemically deposited nanowires. © 2009 American Institute of Physics. doi:10.1063/1.3211294

ZnO/CdSe nanowires and nanotubes: formation, properties and applications

Abstract: Arrays of vertically aligned ZnO nanotubes were obtained in two steps by combining the electrochemical deposition and chemical dissolution of the nanowire core. In the first step arrays of nanowires (diameter ∼ 200 nm, length ∼ 1.5 μm) were electrodeposited from O2 reduction in aqueous zinc chloride solutions. In the second step, the chemical dissolution of the nanowire core in a neutral pH chloride solution led to the formation of arrays of ZnO nanotubes with the same external dimensions and a wall thickness of ∼ 35 nm. Nanowires and nanotubes exhibited single-crystalline nature and no spurious phases were detected. The light scattering in both types of arrays was studied, emphasizing its influence on the sensitization of ZnO to solar light, by using a CdSe nanocrystalline coating as a light absorber. For a constant amount of CdSe deposited, the ZnO/CdSe nanowire arrays had a slightly higher effective absorption of the solar light (86% in the 400–725 nm range of (AM1.5) solar spectrum) than the ZnO/CdSe nanotubes (84%). However, ZnO/CdSe nanotubes exhibit a more attractive morphology for the transfer of electrical charge carriers and arrays of ZnO nanotubes appear to be very promising building blocks for nanostructured solar cells. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)