Advanced Functional Materials

Cover image for Advanced Functional Materials

May, 2004

Volume 14, Issue 5

Pages 403–514

    1. Materials for Multibit-per-Site Optical Data Storage (pages 409–415)

      J. Wang and G. D. Stucky

      Version of Record online: 18 MAY 2004 | DOI: 10.1002/adfm.200400032

      An approach for multibit-per-site optical data storage has been proposed and demonstrated using mesostructured composite films incorporated with uniformly dispersed photoacid generator and pH-sensitive dye molecules (see Figure).

    2. Enhanced Photoelectrochemistry in CdS/Au Nanoparticle Bilayers (pages 416–424)

      L. Sheeney-Haj-Ichia, S. Pogorelova, Y. Gofer and I. Willner

      Version of Record online: 18 MAY 2004 | DOI: 10.1002/adfm.200305430

      Enhanced photocurrents are observed in Au-nanoparticle/CdS-nanoparticle bilayer assemblies bridged by molecular crosslinkers. Maximum photocurrent is observed in a system crosslinked by a bipyridinium electron relay (see Figure), quantum yield, φ = 0.1. The enhanced photocurrents are attributed to vectorial electron transfer in the systems that facilitates charge separation.

    3. Relating the Morphology of Poly(p-phenylene vinylene)/Methanofullerene Blends to Solar-Cell Performance (pages 425–434)

      J. K. J. van Duren, X. Yang, J. Loos, C. W. T. Bulle-Lieuwma, A. B. Sieval, J. C. Hummelen and R. A. J. Janssen

      Version of Record online: 18 MAY 2004 | DOI: 10.1002/adfm.200305049

      The morphology of polymer solar cells consisting of a blend of a poly(p-phenylene vinylene) and a methanofullerene is resolved in three dimensions on a nanometer scale and related to cell performance. Phase separation seen in atomic force micrographs (see Figure) is crucial for optimum energy conversion efficiency. The results are interpreted in terms of a hierarchical structure of two interpenetrating networks of fullerenes at different length scales.

    4. Interface Engineering for Solid-State Dye-Sensitized Nanocrystalline Solar Cells: The Use of Ion-Solvating Hole-Transporting Polymers (pages 435–440)

      S. A. Haque, T. Park, C. Xu, S. Koops, N. Schulte, R. J. Potter, A. B. Holmes and J. R. Durrant

      Version of Record online: 18 MAY 2004 | DOI: 10.1002/adfm.200400043

      Fabrication of novel nanostructured multicomponent films using a lithium ion doped dual-functional hole-transporting material (Li+–DFHTM, see Figure) to allow molecular level control of local chemical composition at nanostructured inorganic/organic semiconductor heterojunctions is reported. The Li+–DF-HTM layers provide a new and versatile control of the interface electrostatics, and consequently charge transfer, at the heterojunction.

    5. The Influence of the Phase Morphology on the Optoelectronic Properties of Light-Emitting Electrochemical Cells (pages 441–450)

      F. P. Wenzl, P. Pachler, C. Suess, A. Haase, E. J. W. List, P. Poelt, D. Somitsch, P. Knoll, U. Scherf and G. Leising

      Version of Record online: 18 MAY 2004 | DOI: 10.1002/adfm.200305431

      Light-emitting electrochemical cells (LECs) operate via the accumulation of ionic species provided by the electrolyte at the electrodes. It is shown here that different conjugated polymer/electrolyte phase-separation processes (see Figure), in combination with the complexation tendencies of the ionic species and the ionic transport numbers, influence the performance of LECs. This opens up new strategies for tuning the optoelectronic properties of ion-supported organic electronic devices.

    6. Extracting Light from Polymer Light-Emitting Diodes Using Stamped Bragg Gratings (pages 451–456)

      J. M. Ziebarth, A. K. Saafir, S. Fan and M. D. McGehee

      Version of Record online: 18 MAY 2004 | DOI: 10.1002/adfm.200305070

      An increase in the external efficiency of polymer light-emitting diodes (LEDs) by coupling out waveguided light with Bragg gratings is described. The waveguide modes in an LED structure are modeled, and it is demonstrated that optimizing layer thicknesses and reducing waveguide absorption can enhance grating outcoupling. The Figure shows a grating, created by a soft-lithography technique, which minimizes changes to the conventional LED structure.

    7. Reversible Cluster Formation of Colloidal Nanospheres by Interparticle Photodimerization (pages 457–463)

      X. Yuan, K. Fischer and W. Schärtl

      Version of Record online: 18 MAY 2004 | DOI: 10.1002/adfm.200305084

      Crosslinked spherical nanoparticles labeled with photoreactive dye molecules have been prepared via polycondensation. Upon irradiation of dilute solutions of these nanoparticles with UV light, photodimerization causes the formation of colloidal clusters consisting of chemically bound individual nanospheres (see Figure), which can be destroyed by irradiation with UV light of shorter wavelengths than that used for their formation.

    8. Single-Crystalline Gallium Nitride Microspindles: Synthesis, Characterization, and Thermal Stability (pages 464–470)

      F. Xu, Y. Xie, X. Zhang, S. Zhang, X. Liu, W. Xi and X. Tian

      Version of Record online: 18 MAY 2004 | DOI: 10.1002/adfm.200305004

      High-quality wurtzite GaN microspindles (see Figure) are synthesized on a large scale via a solid-state reaction of GaI3, NaNH2, and NH4Cl in a sealed system at 500 °C for 6 h. Microspindle growth may be controlled by linear kinetics with a driving force proportional to the difference between local super-saturation and equilibrium chemical potential.

    9. Nanoporous Low-κ Polyimide Films via Poly(amic acid)s with Grafted Poly(ethylene glycol) Side Chains from a Reversible Addition–Fragmentation Chain-Transfer-Mediated Process (pages 471–478)

      Y. Chen, W. Wang, W. Yu, Z. Yuan, E.-T. Kang, K.-G. Neoh, B. Krauter and A. Greiner

      Version of Record online: 18 MAY 2004 | DOI: 10.1002/adfm.200305050

      Nanoporous low-κ polyimide (PI) films with well-defined pore-size distribution and well-preserved PI backbones (see Figure) are prepared from the reversible addition–fragmentation chain-transfer (RAFT)-mediated graft copolymers of poly(amic acid)s with thermally labile poly(ethylene glycol) methyl ether methacrylate side chains. The dielectric constant of the film can be varied by varying the graft concentration of the side chains.

    10. Alkyl Substituent Effects on the Conductivity of Polyaniline (pages 479–486)

      N. A. Zaidi, J. P. Foreman, G. Tzamalis, S. C. Monkman and A. P. Monkman

      Version of Record online: 18 MAY 2004 | DOI: 10.1002/adfm.200305488

      The oxidative polymerization of aniline hydrochloride derivatives in water at low temperature is studied without lithium chloride. The resulting polymers have high molecular weight but the conductivity of the acid-doped films is strongly dependent on the alkyl-substituted chain at the 2-positions. The cause of these effects is investigated using density functional theory methods, which show that the reduction in conductivity observed on increasing alkyl bulk is due to steric and not electronic effects.

    11. Efficient Load Transfer to Polymer-Grafted Multiwalled Carbon Nanotubes in Polymer Composites (pages 487–491)

      G. L. Hwang, Y.-T. Shieh and K. C. Hwang

      Version of Record online: 18 MAY 2004 | DOI: 10.1002/adfm.200305382

      When polymer-grafted carbon nanotubes (CNTs) are used to reinforce poly(methyl methacrylate) (PMMA) composites, an applied load is efficiently transferred to the CNTs, leading to their breaking (see Figure) instead of sliding as is usually observed. The storage modulus of a 20 wt.-% PMMA-grafted CNT composite is increased by ∼29 GPa (∼1100 %)

    12. Solventless Polymerization to Grow Thin Films on Solid Substrates (pages 492–500)

      H. Gu, D. Fu, L.-T. Weng, J. Xie and B. Xu

      Version of Record online: 18 MAY 2004 | DOI: 10.1002/adfm.200305094

      A simple, additive, and solventless process (see Figure) based on catalytic polymerization and soft lithography generates patterned polymer films that serve as an excellent etching resistant. This process offers a complementary, useful alternative to spin-coating and plasma polymerization.

    13. Enhanced Dielectric and Electromechanical Responses in High Dielectric Constant All-Polymer Percolative Composites (pages 501–506)

      C. Huang and Q. Zhang

      Version of Record online: 18 MAY 2004 | DOI: 10.1002/adfm.200305021

      An all-polymer percolative composite that exhibits a very high dielectric constant (> 7000) is reported. The composite makes it possible to induce a high electromechanical response under a much-reduced electric field in field-effect electroactive polymer (EAP) actuators (a strain of 2.65% with an elastic energy density of 0.18 J cm–3 can be achieved under a field of 16 MV m–1).

    14. Lamellar Mesostructured Silicas with Chemically Significant Hierarchical Morphologies (pages 507–512)

      A. J. Karkamkar, S.-S. Kim, S. D. Mahanti and T. J. Pinnavaia

      Version of Record online: 18 MAY 2004 | DOI: 10.1002/adfm.200305085

      The assembly of lamellar mesostructured silicas from electrically neutral and unsymmetrical CnH2n+1NH(CH2)mNH2 Gemini surfactants (n = 10, 12, 14 and m = 3, 4) is reported. The silicas exhibit different lamellar curvatures (see Figure) and hierarchical structures that minimize the diffusion path length for accessing the framework pores.