Advanced Materials

Cover image for Advanced Materials

August, 2000

Volume 12, Issue 16

Pages 1161–1225

    1. Reactions and Reactivity in Self-Assembled Monolayers (pages 1161–1171)

      V. Chechik, R. M. Crooks and C. J. M. Stirling

      Version of Record online: 17 AUG 2000 | DOI: 10.1002/1521-4095(200008)12:16<1161::AID-ADMA1161>3.0.CO;2-C

      Self-assembled monolayers (SAMs) are excellent models for studying interfacial reactions. Here monolayer chemistry is reviewed, focusing on the features that have no analogues in solution chemistry. The growth of surface-attached polymers, intrafilm reactions such as that shown in the Figure, photochemistry, and reactivity issues are all discussed.

    2. Polymer Gel Nanoparticle Networks (pages 1173–1176)

      Z. Hu, X. Lu, J. Gao and C. Wang

      Version of Record online: 17 AUG 2000 | DOI: 10.1002/1521-4095(200008)12:16<1173::AID-ADMA1173>3.0.CO;2-Z

      A new class of nanostructured polymer gel is reported here, in which polymer nanoparticles, rather than monomers, are covalently crosslinked. Since their building blocks are nanoparticles, the thus formed networks have novel and unique properties compared with conventional gels, for example, a very high surface area for better bioadhesion, and a uniform and tunable mesh size for controlled drug delivery. Several networks are presented, including one with a fast shrinkage rate, a colored network, and a co-nanoparticle network as a potential multifunctional drug delivery carrier.

    3. Conjugated-Polymer Photonic Crystals (pages 1176–1180)

      M. Deutsch, Yu. A. Vlasov and D. J. Norris

      Version of Record online: 17 AUG 2000 | DOI: 10.1002/1521-4095(200008)12:16<1176::AID-ADMA1176>3.0.CO;2-H

      Three-dimensional photonic crystals made from an organic semiconductor—poly(p-phenylenevinylene) (PPV)—are studied here. Their synthesis (via colloidal assembly), physical appearance, and optical properties are investigated. The Figure shows optical micrographs of a polished PPV photonic crystal under ultraviolet (top) and white (bottom) light illumination, indicating fluorescence and optical diffraction, respectively (see also cover).

    4. New Chiral Nematic Materials with Photovariable Helical Supramolecular Structure for Reversible Optical Data Recording (pages 1180–1183)

      A. Yu. Bobrovsky, N. I. Boiko, V. P. Shibaev and J. Springer

      Version of Record online: 17 AUG 2000 | DOI: 10.1002/1521-4095(200008)12:16<1180::AID-ADMA1180>3.0.CO;2-E

      Chiral nematic materials with reversibly controlled helical pitch are synthesized here and their photo-optical properties are investigated. Selective light reflection in the green region is observed and patterns such as that shown in the Figure can be recorded. High fatigue resistance is also demonstrated for these materials, which can undergo repeated record/erase cycles without loss of color characteristics.

    5. Sonochemical Synthesis of Mesoporous Titanium Oxide with Wormhole-like Framework Structures (pages 1183–1186)

      Y. Wang, X. Tang, L. Yin, W. Huang, Y. Rosenfeld Hacohen and A. Gedanken

      Version of Record online: 17 AUG 2000 | DOI: 10.1002/1521-4095(200008)12:16<1183::AID-ADMA1183>3.0.CO;2-X

      Ultrasound irradiation is proving to be an excellent method for the synthesis of mesoporous oxides. Here is reported the preparation of titania containing a framework of wormholes—a structural motif of importance for catalysis. Using ultrasonication with a long-chain organic amine as a structure-directing agent, the synthesis was complete in a few hours (the Figure shows particles of the as-prepared material).

    6. Oriented Silicon Carbide Nanowires: Synthesis and Field Emission Properties (pages 1186–1190)

      Z. Pan, H.-L. Lai, F. C. K. Au, X. Duan, W. Zhou, W. Shi, N. Wang, C.-S. Lee, N.-B. Wong, S.-T. Lee and S. Xie

      Version of Record online: 17 AUG 2000 | DOI: 10.1002/1521-4095(200008)12:16<1186::AID-ADMA1186>3.0.CO;2-F

      Arrays of oriented silicon carbide (SiC) nanowires are synthesized by reacting stable carbon nanotubes—which act as both template and reagent—with SiO. Field emission measurements on the nanowires indicate that the arrays are excellent field emitters, technologically useful field emission current densities being produced at very low electric fields. The results suggest that the oriented nanowires may have potential uses in vacuum microelectronic devices in addition to more conventional applications as strengthening in composites (replacing SiC whiskers, which have lower elasticity and strength).

    7. Synthesis of Macroscopically Long Ropes of Well-Aligned Single-Walled Carbon Nanotubes (pages 1190–1192)

      C. Liu, H.-M. Cheng, H. T. Cong, F. Li, G. Su, B. L. Zhou and M. S. Dresselhaus

      Version of Record online: 17 AUG 2000 | DOI: 10.1002/1521-4095(200008)12:16<1190::AID-ADMA1190>3.0.CO;2-C

      Ropes of aligned single-walled carbon nanotubes (SWNTs) up to 10 cm in length (see Figure) have been synthesized here by the hydrogen and argon arc discharge method. The nanotubes are characterized by SEM, TEM, and Raman scattering, and their porosity is investigated. Measurements of the properties of SWNTs can be conveniently made on these very long ropes, which should also find practical applications.

    8. Gel-Forming of Nickel Powders from Aqueous Slurries (pages 1192–1195)

      A. J. Sánchez-Herencia, A. J. Millán, M. I. Nieto and R. Moreno

      Version of Record online: 17 AUG 2000 | DOI: 10.1002/1521-4095(200008)12:16<1192::AID-ADMA1192>3.0.CO;2-0

      Dense and porous metallic compacts can be fabricated by a colloidal technique in water, as demonstrated here. Through the use of a novel gelling binder—carrageenan—nickel parts with controlled porosity (see Figure) are obtained. This is an important achievement as, although the colloidal approach has proved very successful for the processing of ceramics, its implementation in metal powder processing has been problematic.

    9. Polar Alignment in Spin-Coated Carbazole Main- and Side-Chain Polymer Films (pages 1196–1199)

      H. Kimura-Suda, Y. Zhang, T. Sassa, T. Wada and H. Sasabe

      Version of Record online: 17 AUG 2000 | DOI: 10.1002/1521-4095(200008)12:16<1196::AID-ADMA1196>3.0.CO;2-D

      A new method for preparing polar-aligned films, utilizing spin-coating without an electric field, is presented here. The technique was applied to a carbazole-based polymer with nitrostilbene chromophores as side groups. Phase measurements of second harmonic generation indicate that the chromophores are spontaneously aligned parallel to the direction of the centrifugal force (see Figure).

    10. Are Low-Coordinating Anions of Interest as Doping Agents in Organic Conducting Polymers? (pages 1199–1202)

      C. Masalles, S. Borrós, C. Viñas and F. Teixidor

      Version of Record online: 17 AUG 2000 | DOI: 10.1002/1521-4095(200008)12:16<1199::AID-ADMA1199>3.0.CO;2-W

      Polypyrrole (PPy) is of great potential importance due to its excellent conductive properties; however, a major obstacle to commercialization (like many synthetic metals) is its poor stability, especially to oxidation. Here is reported a new synthesis of PPy in the presence of the cobaltabisdicarbollide anion (see Figure), whose uniform distribution throughout the polymer leads to a dramatic improvement in the overoxidation threshold.

    11. Large Photoinduced Birefringence in Azo Dye/Polyion Films Assembled by Electrostatic Sequential Adsorption (pages 1202–1205)

      S. Bian, J.-A. He, L. Li, J. Kumar and S. K. Tripathy

      Version of Record online: 17 AUG 2000 | DOI: 10.1002/1521-4095(200008)12:16<1202::AID-ADMA1202>3.0.CO;2-C

      Large and stable photoinduced birefringenceis observed in thin films of Congo red (CR, see Figure) and poly(dimethyldiallylammonium chloride) (PDAC, see Figure), fabricated by electrostatic sequential absorption. Investigations indicate that only a small contribution to the birefringence is from photoinduced alignment of the azobenzene chromophores, the larger contribution being attributed to polarization-selective degradation.

    12. A New Organic Conductor and a Novel Structural Phase Transition in the BEDT-TTF Trihalide Family (pages 1205–1210)

      E. Laukhina, J. Vidal-Gancedo, S. Khasanov, V. Tkacheva, L. Zorina, R. Shibaeva, J. Singleton, R. Wojciechowski, J. Ulanski, V. Laukhin, J. Veciana and C. Rovira

      Version of Record online: 17 AUG 2000 | DOI: 10.1002/1521-4095(200008)12:16<1205::AID-ADMA1205>3.0.CO;2-V

      A new quasi-2D molecular conductorbased on BEDT-TTF with an assembly of the trihalide anions I2Br, IBr2, and BrICl is presented here. This set of anions promotes the formation of α′- and α‴-type conducting layers (see Figure, top) along with a low-temperature α‴[RIGHTWARDS ARROW]β″ transition seen for the first time in BEDT-TTF salts.

    13. Raman Imaging of Single Carbon Nanotubes (pages 1210–1214)

      A. Mews, F. Koberling, T. Basché, G. Philipp, G. S. Duesberg, S. Roth and M. Burghard

      Version of Record online: 17 AUG 2000 | DOI: 10.1002/1521-4095(200008)12:16<1210::AID-ADMA1210>3.0.CO;2-M

      Individual carbon nanotubes (CNTs) have been located and investigated using scanning confocal Raman microscopy. In particular, the geometry of thin bundles and individual single-walled CNTs was able to be examined by combining Raman with scanning force microscopy. Spatially resolved Raman spectroscopy could thus be performed within given bundles, such as those visible in the Figure.

    14. Electrochemical Self-Assembly of Nanoporous ZnO/Eosin Y Thin Films and Their Sensitized Photoelectrochemical Performance (pages 1214–1217)

      T. Yoshida, K. Terada, D. Schlettwein, T. Oekermann, T. Sugiura and H. Minoura

      Version of Record online: 17 AUG 2000 | DOI: 10.1002/1521-4095(200008)12:16<1214::AID-ADMA1214>3.0.CO;2-Z

      The photoactive materials in dye-sensitized solar cells (DSSCs) are conventionally produced by colloid coating and heat treatment followed by dye adsorption by dipping in solution. One disadvantage of this procedure is that only heat-resistant materials can be used. Here the one-step self-assembly of ZnO/eosin Y thin films is reported. It is shown that a large proportion of the incorporated eosin Y dye molecules act as sensitizers, making the films suitable as sensitized photoelectrodes in DSSCs. No heat treatment is required, allowing non-heat-resistant substrates such as flexible conductive plastic films to be used.

    15. Electrochemical Self-Assembly of Dye-Modified Zinc Oxide Thin Films (pages 1219–1222)

      T. Yoshida and H. Minoura

      Version of Record online: 17 AUG 2000 | DOI: 10.1002/1521-4095(200008)12:16<1219::AID-ADMA1219>3.0.CO;2-5

      One-step electrochemical self-assembly is an excellent new method for the construction of hybrid inorganic/organic films for dye-sensitized solar cells (DSSCs). The promising oxide semiconductor zinc oxide can be electrodeposited in the presence of organic dye molecules to give porous thin films with varying morphology suitable for DSSCs (the Figure shows a ZnO film grown in the presence of a tetrasulfophthalocyanine).

    16. High-Strain Actuator Materials Based on Dielectric Elastomers (pages 1223–1225)

      R. Pelrine, R. Kornbluh and G. Kofod

      Version of Record online: 17 AUG 2000 | DOI: 10.1002/1521-4095(200008)12:16<1223::AID-ADMA1223>3.0.CO;2-2

      Dielectric elastomers are a new class of actuator materials that exhibit excellent performance. The principle of operation, as well as methods to fabricate and test these elastomers, is summarized here. The Figure is a sketch of an elastomer film (light gray) stretched on a frame (black) and patterned with an electrode (mid-gray). Upon applying a voltage, the active portion of the elastomer expands and the strain can easily be measured optically.