Advanced Materials

Cover image for Advanced Materials

February, 2000

Volume 12, Issue 3

Pages 167–239

    1. Polymer Network–Stabilized Liquid Crystals (pages 167–181)

      I. Dierking

      Version of Record online: 24 JAN 2000 | DOI: 10.1002/(SICI)1521-4095(200002)12:3<167::AID-ADMA167>3.0.CO;2-I

      The polymerization in a liquid-crystalline phase of a small amount of bifunctional photoreactive monomer can stabilize the orientation of the liquid crystals, as illustrated in the Figure. The formation and properties of these polymer-stabilized liquid crystals (PSLCs) are reviewed and the influence of the preparation conditions on the polymer network morphology and thus the electro-optical performance of the PSLCs are examined.

    2. Near-Field Fluorescence Microscopy of Tris-8-hydroxyquinoline Aluminum Films (pages 183–186)

      G. M. Credo and S. K. Buratto

      Version of Record online: 24 JAN 2000 | DOI: 10.1002/(SICI)1521-4095(200002)12:3<183::AID-ADMA183>3.0.CO;2-Q

      The dependence of the nanoscale optical properties of Alq3 on film morphology (Alq3=tris-8-hydroxyquinoline aluminum) is still poorly understood, although Alq3 is widely used as the emissive layer in organic LEDs. Here near-field scanning optical microscopy (NSOM) is used to probe the local optical and morphological properties of Alq3 films. It is shown that features as small as 10–100 nm can be observed, a resolution not obtained with previously used techniques. Differences in the quality of vacuum-deposited, spin-cast, and drop-cast films are investigated using this technique.

    3. Two-Dimensional Crosslinked Nanoparticle Networks (pages 186–189)

      S. Chen

      Version of Record online: 24 JAN 2000 | DOI: 10.1002/(SICI)1521-4095(200002)12:3<186::AID-ADMA186>3.0.CO;2-E

      Monolayer-protected nanoclusters exhibit good stabilityboth in solution and dry forms and as such are promising materials for nanocircuits and nanodevices. In this article, an efficient method for fabricating 2D crosslinked nanoparticle networks using the Langmuir–Blodgett technique and dithiols as bifunctional linkers is reported. As shown in the Figure, close-packed assemblies are produced.

    4. Trapping Light in Polymer Photodiodes with Soft Embossed Gratings (pages 189–195)

      L. Stolz Roman, O. Inganäs, T. Granlund, T. Nyberg, M. Svensson, M. R. Andersson and J. C. Hummelen

      Version of Record online: 24 JAN 2000 | DOI: 10.1002/(SICI)1521-4095(200002)12:3<189::AID-ADMA189>3.0.CO;2-2

      Increasing the conversion efficiency is very important in photovoltaic devices, as is cheap and simple technology. Here is demonstrated a soft embossing technique for printing a submicrometer grating with an elastomeric mold into an optically active polymer layer in a photovoltaic device (see Figure). The light trapping due to the grating pattern enhances the photoconversion efficiency by more than 25 % at normal light incidence (see also inside front cover).

    5. Synthesis of a High-Permeance NaA Zeolite Membrane by Microwave Heating (pages 195–198)

      X. Xu, W. Yang, J. Liu and L. Lin

      Version of Record online: 24 JAN 2000 | DOI: 10.1002/(SICI)1521-4095(200002)12:3<195::AID-ADMA195>3.0.CO;2-E

      Zeolite membranes with high permeance and separation factors are highly desirable for practical applications. Although, in the past, very good separation factors have been obtained, it has proved difficult to achieve a high permeance. Here a comparative study of microwave versus conventional heating in the hydrothermal synthesis of NaA zeolite membranes is made. It is demonstrated that membranes prepared by microwave heating have not only a higher permeance but also a considerably shorter synthesis time. These observations are rationalized by examining the mechanism of membrane formation.

    6. Mesoporous Yttria–Zirconia and Metal–Yttria–Zirconia Solid Solutions for Fuel Cells (pages 198–202)

      M. Mamak, N. Coombs and G. Ozin

      Version of Record online: 24 JAN 2000 | DOI: 10.1002/(SICI)1521-4095(200002)12:3<198::AID-ADMA198>3.0.CO;2-2

      A new class of binary mesoporous yttria–zirconia(YZ) and ternary mesoporous metal-YZ materials (M=electroactive Ni/Pt) is presented here (the Figure shows PtYZ) that displays the highest surface area of any known form of yttria-stabilized zirconia. These mesoporous materials form as solid solutions and retain their structural integrity to 800 °C, which bodes well for their possible utilization in fuel cells.

    7. Templating Effects in the Growth of Metal-Free Phthalocyanine Polymorphic Double Layers (pages 202–206)

      S. M. Bayliss, S. Heutz, R. Cloots, R. L. Middleton, G. Rumbles and T. S. Jones

      Version of Record online: 24 JAN 2000 | DOI: 10.1002/(SICI)1521-4095(200002)12:3<202::AID-ADMA202>3.0.CO;2-L

      The influence of the first molecular layer on the growth and properties of subsequent layers is examined using different polymorphs of metal-free phthalocyanine (H2Pc). It is shown than the first layer acts as a morphological and structural template, as illustrated by the Figure, which is an Normarski image of a β1/α polymorphic double layer—characteristic β1 domains are seen although the top layer is an α film.

    8. Preparation of Mesoscale Hollow Spheres of TiO2 and SnO2 by Templating Against Crystalline Arrays of Polystyrene Beads (pages 206–209)

      Z. Zhong, Y. Yin, B. Gates and Y. Xia

      Version of Record online: 24 JAN 2000 | DOI: 10.1002/(SICI)1521-4095(200002)12:3<206::AID-ADMA206>3.0.CO;2-5

      Mesoscale hollow spheres of ceramic materials can be prepared by templating an appropriate sol–gel precursor against a crystalline array of monodisperse polystyrene beads, as demonstrated here. Spheres of well-controlled, uniform size and homogeneous wall thickness result, as can be seen from the Figure, which shows the TEM cross-sectional view of an array of TiO2 hollow spheres.

    9. A Topology Map for Novel Vesicle–Polymer Hybrid Architectures (pages 210–213)

      M. Jung, D. H. W. Hubert, P. H. H. Bomans, P. Frederik, A. M. van Herk and A. L. German

      Version of Record online: 24 JAN 2000 | DOI: 10.1002/(SICI)1521-4095(200002)12:3<210::AID-ADMA210>3.0.CO;2-P

      The use of vesicles as templates for the polymerization of inserted monomers gives rise to novel vesicle-polymer hybrid morphologies where a polymer bead is phase-separated from the vesicle bilayer matrix. Complex vesicle–polymer architectures, such as the “wrapped parachute” morphologies shown in the Figure, are synthesized here and then examined using cryo-transmission electron microscopy (see also cover).

    10. Phase Separation of Carbon Nanotubes and Turbostratic Graphite Using a Functional Organic Polymer (pages 213–216)

      J. N. Coleman, A. B. Dalton, S. Curran, A. Rubio, A. P. Davey, A. Drury, B. McCarthy, B. Lahr, P. M. Ajayan, S. Roth, R. C. Barklie and W. J. Blau

      Version of Record online: 24 JAN 2000 | DOI: 10.1002/(SICI)1521-4095(200002)12:3<213::AID-ADMA213>3.0.CO;2-D

      Nanotubes are rich in potential applications, but they are very difficult to purify, and yields are often less than 1 %. The solution presented here is to suspend nanotubes in a polymer matrix, which then acts as a filtration system. Incorporation is achieved by sonication, followed by a period of settling, during which the amorphous material falls out, leaving a highly pure sample of nanotubes (see Figure) that contains virtually no other carbonaceous material.

    11. Tuning the Optoelectronic Properties of Pyridine-Containing Polymers for Light-Emitting Devices (pages 217–222)

      C. Wang, M. Kilitziraki, J. A. H. MacBride, M. R. Bryce, L. E. Horsburgh, A. K. Sheridan, A. P. Monkman and I. D. W. Samuel

      Version of Record online: 24 JAN 2000 | DOI: 10.1002/(SICI)1521-4095(200002)12:3<217::AID-ADMA217>3.0.CO;2-Y

      Increased electron affinity and improved electron-transporting properties are lent to polymers based on pyridine when compared to benzene. Here, the synthesis of new pyridine-containing conjugated polymers, such as those shown in the Figure, are described. Their optical absorption and luminescence spectra in solution and thin films are also investigated as is their potential as electron-transporting layers in LEDs.

    12. Poly(3,4-alkylenedioxypyrrole)s as Highly Stable Aqueous-Compatible Conducting Polymers with Biomedical Implications (pages 222–225)

      C. A. Thomas, K. Zong, P. Schottland and J. R. Reynolds

      Version of Record online: 24 JAN 2000 | DOI: 10.1002/(SICI)1521-4095(200002)12:3<222::AID-ADMA222>3.0.CO;2-D

      Polypyrrole (PPy) may be set to revolutionize biological applications such as tissue engineering and biosensors due to its high electroactivity/conductivity and the water compatibility of its films. However, inherent weaknesses in PPy-based materials arise from defect sites along the PPy polymer backbone, and its instability to reduction by biologically relevant reducing agents such as dithiothreitol (DTT) and glutathione. Here is presented a family of electron-rich poly(3,4-alkylenedioxypyrrole)s that address these structural weaknesses and are stable in the conducting, oxidized form, rendering them immune to strong biological reducing agents.

    13. Materials and Fabrication Needs for Low-Cost Organic Transistor Circuits (pages 227–230)

      Z. Bao

      Version of Record online: 24 JAN 2000 | DOI: 10.1002/(SICI)1521-4095(200002)12:3<227::AID-ADMA227>3.0.CO;2-U

      The key building blocks of organic transistor circuits, organic thin-film field-effect transistors (FETs), are reviewed in this article. Recent important materials-related research on n-channel and solution-processable semiconductors (e.g., the p-channel semiconductor dihexyl-α-pentathiophene shown in the Figure) and dielectric materials are addressed as are future needs, such as practical reel-to-reel processes.

    14. Vanadium Oxide Nanotubes—A New Flexible Vanadate Nanophase (pages 231–234)

      H.-J. Muhr, F. Krumeich, U. P. Schönholzer, F. Bieri, M. Niederberger, L. J. Gauckler and R. Nesper

      Version of Record online: 24 JAN 2000 | DOI: 10.1002/(SICI)1521-4095(200002)12:3<231::AID-ADMA231>3.0.CO;2-D

      Vanadium oxide nanotubes have recently been discovered as the main product of a sol-gel reaction that is followed by hydrothermal treatment in the presence of air, during which vanadium oxide sheets roll up, giving rise to the scroll morphology visible in the Figure. The scrolls are highly flexible, permitting numerous exchange reactions, and can be aligned using micromolding in capillaries.

    15. Hyperbranched Polyether Polyols: A Modular Approach to Complex Polymer Architectures (pages 235–239)

      A. Sunder, R. Mülhaupt, R. Haag and H. Frey

      Version of Record online: 24 JAN 2000 | DOI: 10.1002/(SICI)1521-4095(200002)12:3<235::AID-ADMA235>3.0.CO;2-Y

      A versatile modular system for complex branched polymer architectures has been developed through exploitation of the multibranching polymerization chemistry of glycidol. This report summarizes recent advances in the preparation of these novel polymers and describes the modular concept used to tailor their topology to give functional materials, such as the dye-loaded molecular nanocapsule depicted in the Figure.