Advanced Materials

Cover image for Vol. 13 Issue 20

October, 2001

Volume 13, Issue 20

Pages 1523–1585

    1. Siloxane and Carbosiloxane Based Dendrimers: Synthesis, Reaction Chemistry, and Potential Applications (pages 1523–1540)

      H. Lang and B. Lühmann

      Version of Record online: 4 OCT 2001 | DOI: 10.1002/1521-4095(200110)13:20<1523::AID-ADMA1523>3.0.CO;2-P

      Recent developments in the field of siloxane and carbosiloxane dendrimers with the silicon atoms as the branching points (see Figure) are discussed in this review. It treats in a comprehensive way the divergent growth method for the synthesis of the Si–O- and Si–O–C-based dendrimers, including their reaction chemistry, their theoretical and physical descriptions, as well as their potential applications in the area of materials science.

    2. New Percolative BaTiO3–Ni Composites with a High and Frequency-Independent Dielectric Constant (ϵr ≈ 80000) (pages 1541–1544)

      C. Pecharromán, F. Esteban-Betegón, J. F. Bartolomé, S. López-Esteban and J. S. Moya

      Version of Record online: 4 OCT 2001 | DOI: 10.1002/1521-4095(200110)13:20<1541::AID-ADMA1541>3.0.CO;2-X

      A novel capacitor devicewith a high, frequency-independent dielectric constant has been fabricated by a simple powder processing route. A mixture of microparticles of ferroelectric BaTiO3 and de-passivated metallic nickel was sintered to yield percolative composites in which the system of conducting particles separated by insulator layers (see Figure for an SEM image) exhibits a dielectric constant higher than that of either component.

    3. Novel Macroscopic Self-Organization in Polymer Gels (pages 1544–1548)

      S. Varghese, A. K. Lele, D. Srinivas, M. Sastry and R. A. Mashelkar

      Version of Record online: 4 OCT 2001 | DOI: 10.1002/1521-4095(200110)13:20<1544::AID-ADMA1544>3.0.CO;2-F

      Fully reversible macroscopic self-organization is observed in polymeric gels based on acryloyl derivatives of amino acids. Only certain gels, which have a critical balance of hydrophilic and hydrophobic groups in their chemical structure, demonstrate the self-organization from solid cylinder to hollow sphere (see Figure). These gels can be used in novel applications such as the controlled release of drugs and chemicals.

    4. Synthesis and Spectroscopic Characterization of Highly Conducting BF3-Doped Polyaniline (pages 1548–1551)

      D. Chaudhuri, A. Kumar, I. Rudra and D. D. Sarma

      Version of Record online: 4 OCT 2001 | DOI: 10.1002/1521-4095(200110)13:20<1548::AID-ADMA1548>3.0.CO;2-S

      A highly conducting polyaniline, doped with a Lewis acid, boron trifluoride, has been synthesized. Doping involves a transfer of the lone pair of electrons from the imine nitrogen of the polyaniline to the B center, leading to a change in the hybridization at the B site from sp2 to sp3. Various spectroscopic techniques, in conjunction with ab initio calculations for geometry optimizations, are used to characterize the sample. These techniques all confirm the ability of this electron-deficient molecule to dope polyaniline very effectively, yielding a remarkably high conductivity over a wide temperature range.

    5. Large Area Photonic Crystal Slabs for Visible Light with Waveguiding Defect Structures: Fabrication with Focused Ion Beam Assisted Laser Interference Lithography (pages 1551–1554)

      L. Vogelaar, W. Nijdam, H. A. G. M. van Wolferen, R. M. de Ridder, F. B. Segerink, E. Flück, L. Kuipers and N. F. van Hulst

      Version of Record online: 4 OCT 2001 | DOI: 10.1002/1521-4095(200110)13:20<1551::AID-ADMA1551>3.0.CO;2-V

      Extended photonic crystal slabs with light-guiding defects have been created by a combination of laser interference lithography (LIL) and local focused ion beam (FIB) assisted deposition. Large area, highly uniform photonic crystal slabs for visible light are thus made possible. The Figure shows a freestanding Si3N4–air photonic crystal with a light-guiding defect line running along the center of the slab (total length = 1 mm).

    6. Poly(3,4-ethylenedioxythiophene)-Based Glucose Biosensors (pages 1555–1557)

      A. Kros, S. W. F. M. van Hövell, N. A. J. M. Sommerdijk and R. J. M. Nolte

      Version of Record online: 4 OCT 2001 | DOI: 10.1002/1521-4095(200110)13:20<1555::AID-ADMA1555>3.0.CO;2-7

      Amperometric biosensors for the recognition of glucose oxidase (GOx) based on poly(3,4-ethylenedioxythiophene) (PEDOT) have for the first time been fabricated and are presented in this communication. This biosensor has potential applications for long-term glucose measurements, e.g., in the treatment of diabetes. The Figure shows the strong electrostatic binding of GOx to a matrix of PEDOT and poly(N-methyl-4-pyridine) (PMVP) (see also inside front cover).

    7. Luminescence Properties of Nanocrystalline Y2O3:Eu (pages 1557–1560)

      G. Wakefield, E. Holland, P. J. Dobson and J. L. Hutchison

      Version of Record online: 4 OCT 2001 | DOI: 10.1002/1521-4095(200110)13:20<1557::AID-ADMA1557>3.0.CO;2-W

      Y2O3:Eu nanocrystals in the size range 70–100 nm have been synthesized with a photoluminescence efficiency 10–20 % higher than that of the commercial bulk material. The Figure shows nanocrystalline Y2O3:Eu after firing of the precursor material. It can be seen that the crystals are structurally perfect, i.e., no defects are found within the crystal structure.

    8. How to Prepare Tunable Planar Molecular Chemical Gradients (pages 1560–1563)

      K. Efimenko and J. Genzer

      Version of Record online: 4 OCT 2001 | DOI: 10.1002/1521-4095(200110)13:20<1560::AID-ADMA1560>3.0.CO;2-Z

      Mechanically assembled monolayers (MAMs) can be employed to adjust the surface density of the initiators and consequently that of molecular gradients prepared on flexible supports. The steepness and the position of the gradient of molecules on a substrate are fine-tuned by a combination of grafting and mechanical manipulation of the films. Planar molecular gradients ranging from several millimeters to several centimeters can thus be fabricated. In addition, the wetting properties of the hydrophobic part of the substrate can be adjusted by altering the chemical nature of the films.

    9. Effect of Gas Exposure on Field Emission Properties of Carbon Nanotube Arrays (pages 1563–1567)

      S. C. Lim, Y. C. Choi, H. J. Jeong, Y. M. Shin, K. H. An, D. J. Bae, Y. H. Lee, N. S. Lee and J. M. Kim

      Version of Record online: 4 OCT 2001 | DOI: 10.1002/1521-4095(200110)13:20<1563::AID-ADMA1563>3.0.CO;2-H

      Carbon nanotubeshave many advantages over conventional semiconductor and metal emitters for field emission displays (FEDs). However, the origin of the current saturation seen in carbon nanotubes at high fields is poorly understood. Here the effect of gas adsorbates on the field emission properties of patterned carbon nanotube arrays, such as the one shown in the Figure, is investigated.

    10. Size-Selective Growth of Nanoscale Tetrathiafulvalene Bromide Crystallites on Platinum Particles (pages 1567–1570)

      F. Favier, H. Liu and R. M. Penner

      Version of Record online: 4 OCT 2001 | DOI: 10.1002/1521-4095(200110)13:20<1567::AID-ADMA1567>3.0.CO;2-U

      (TTF)Br crystallitesthat nucleate and grow on platinum particles exhibit widths that are linearly related to the diameter of the platinum particles on which they grow. Populations of long (TTF)Br crystallites having a predetermined width can be prepared by electrodeposition onto surfaces covered with size-monodispersed platinum catalyst particles. The Figure shows an SEM image of a (TTF)Br nanocrystallite grown on a cluster of Pt particles.

    11. One-Step, Micrometer-Scale Organization of Nano- and Mesoparticles Using Holographic Photopolymerization: A Generic Technique (pages 1570–1574)

      R. A. Vaia, C. L. Dennis, L. V. Natarajan, V. P. Tondiglia, D. W. Tomlin and T. J. Bunning

      Version of Record online: 4 OCT 2001 | DOI: 10.1002/1521-4095(200110)13:20<1570::AID-ADMA1570>3.0.CO;2-X

      Holographic photopolymerization is a flexible, simple, one-step technique to create defect-free, sub-micrometer patterns of particles over large dimensions. These permanent structures can be formed in a matter of seconds. The resulting Bragg gratings exhibit substantial diffraction efficiencies. The Figure shows a cross-sectional fracture surface of a transmission grating formed using clay powder.

    12. Aluminum Oxide Photonic Crystals Grown by a New Hybrid Method (pages 1574–1577)

      I. Mikulskas, S. Juodkazis, R. Tomas̆iūnas and J. G. Dumas

      Version of Record online: 4 OCT 2001 | DOI: 10.1002/1521-4095(200110)13:20<1574::AID-ADMA1574>3.0.CO;2-9

      A simple methodfor the fabrication of anodic aluminum oxide films (AOFs) with perfectly ordered structures (see Figure) is presented by these authors. A common optical grating is used to prepattern the aluminum substrate, which is subsequently anodized under mild conditions to yield an AOF with a photonic bandgap in the visible region.

    13. Titanium Dioxide Tubes from Sol–Gel Coating of Electrospun Polymer Fibers (pages 1577–1579)

      R. A. Caruso, J. H. Schattka and A. Greiner

      Version of Record online: 4 OCT 2001 | DOI: 10.1002/1521-4095(200110)13:20<1577::AID-ADMA1577>3.0.CO;2-S

      Electrospun polymer fibers can be coated with amorphous titanium dioxide using a sol–gel coating technique. After removal of the organic material by thermal treatment hollow titania fibers are produced. The sol–gel coating is able to reproduce the finer details of the fiber, e.g., the Figure shows how oval nodules that were indentations on the initial polymer are mimicked in the final inorganic structure of the titania fibers (see also images on the front cover).

    14. Novel Route to Nanoparticle Synthesis by Salt-Assisted Aerosol Decomposition (pages 1579–1582)

      B. Xia, I. W. Lenggoro and K. Okuyama

      Version of Record online: 4 OCT 2001 | DOI: 10.1002/1521-4095(200110)13:20<1579::AID-ADMA1579>3.0.CO;2-G

      Controllability of particle size,chemical composition, and crystallinity are offered by the simple, general method for the synthesis of nanoparticles described here. A modified aerosol decomposition process is utilized in which salts are added to separate the nanocrystallites, resulting in nanoparticles of narrow size distribution (see Figure) and superior properties.

    15. Conductive Polyaniline/Silica Hybrids from Sol–Gel Process (pages 1582–1585)

      Y. Wang, X. Wang, J. Li, Z. Mo, X. Zhao, X. Jing and F. Wang

      Version of Record online: 4 OCT 2001 | DOI: 10.1002/1521-4095(200110)13:20<1582::AID-ADMA1582>3.0.CO;2-J

      A hybrid material with a conductive organic network in an inorganic matrix has been prepared by in-situ hydrolysis/polycondensation of TEOS in an aqueous solution of a solubilized polyaniline. Due to intense hydrogen bonding (indicated by 29Si NMR and FTIR) the conductive polymer is very well dispersed in the silica matrix. The Figure shows SEM images of a 46/54 wt.-% hybrid at two temperatures (left 20 °C, right 100 °C).