Advanced Materials

Cover image for Advanced Materials

May, 2000

Volume 12, Issue 9

Pages 617–681

    1. Auxetic Materials: Functional Materials and Structures from Lateral Thinking! (pages 617–628)

      K. E. Evans and A. Alderson

      Version of Record online: 17 APR 2000 | DOI: 10.1002/(SICI)1521-4095(200005)12:9<617::AID-ADMA617>3.0.CO;2-3

      Materials that become thicker when stretched and thinner when compressed are the subject of this review. The theory behind the counterintuitive behavior of these so-called auxetic materials is discussed, and examples and applications are examined. For example, blood vessels made from an auxetic material will tend to increase in wall thickness (rather than decrease) in response to a pulse of blood, thus preventing rupture of the vessel (see Figure).

    2. Highly Anisotropically Self-Assembled Structures of para-Sexiphenyl Grown by Hot-Wall Epitaxy (pages 629–633)

      A. Andreev, G. Matt, C. J. Brabec, H. Sitter, D. Badt, H. Seyringer and N. S. Sariciftci

      Version of Record online: 17 APR 2000 | DOI: 10.1002/(SICI)1521-4095(200005)12:9<629::AID-ADMA629>3.0.CO;2-S

      Highly anisotropic films of needle-like crystallinepara-sexiphenyl (PSP)—a promising candidate for the electroactive layer in organic light-emitting diodes (LEDs)—can be produced using hot-wall epitaxy, as demonstrated here (see Figure). Optical dichroic ratios of ≈11 in absorption and up to 14 in emission are measured, which is of great significance for the development of polarized LEDs.

    3. Electron Transport Properties of Nanocrystals: Isolated, and “Supra”-Crystalline Phases (pages 633–637)

      A. Taleb, F. Silly, A. O. Gusev, F. Charra and M.-P. Pileni

      Version of Record online: 17 APR 2000 | DOI: 10.1002/(SICI)1521-4095(200005)12:9<633::AID-ADMA633>3.0.CO;2-B

      Silver nanocrystals (NCs) deposited on an Au (111) substrate have been investigated using scanning tunneling microscopy. The electron transport properties are presented for the particles as isolated NCs, in self-assembled 2D (see Figure) and 3D superlattices. The electronic behavior is found to vary markedly, the monolayer showing both metallic and Coulomb blockade contributions, while NCs in fcc superlattices show ohmic behavior.

    4. Polymer, Metal, and Hybrid Nano- and Mesotubes by Coating Degradable Polymer Template Fibers (TUFT Process) (pages 637–640)

      M. Bognitzki, H. Hou, M. Ishaque, T. Frese, M. Hellwig, C. Schwarte, A. Schaper, J. H. Wendorff and A. Greiner

      Version of Record online: 17 APR 2000 | DOI: 10.1002/(SICI)1521-4095(200005)12:9<637::AID-ADMA637>3.0.CO;2-W

      Coating extremely thin degradable template polymer fibers with the desired wall materials forms the basis of the straightforward and highly versatile method described here for the production of polymer, metal, and hybrid nano- and mesotubes. Tubes with highly structured inner surfaces (see Figure) may be fabricated, which is of great interest for applications requiring large surface/volume ratios (see also cover).

    5. Ordered Colloidal Nanoalloys (pages 640–643)

      C. J. Kiely, J. Fink, J. G. Zheng, M. Brust, D. Bethell and D. J. Schiffrin

      Version of Record online: 17 APR 2000 | DOI: 10.1002/(SICI)1521-4095(200005)12:9<640::AID-ADMA640>3.0.CO;2-J

      Colloidal alloy superlattices of two different nanoclusters are demonstrated here for the first time. Thiol-functionalized Ag and Au nanoclusters were prepared separately in toluene before mixing and solvent evaporation. For certain Au/Ag proportions, the particles spontaneously self-organized into ordered 2D arrays, which can be seen in the bright field STEM image in the Figure.

    6. Microstructured TiO2 Templates for the Preparation of Size-Controlled Bryopsis Protoplasts as Cell Models (pages 643–646)

      T. Tatsuma, A. Ikezawa, Y. Ohko, T. Miwa, T. Matsue and A. Fujishima

      Version of Record online: 17 APR 2000 | DOI: 10.1002/(SICI)1521-4095(200005)12:9<643::AID-ADMA643>3.0.CO;2-7

      Microstructured TiO2 films with hemispheric pores have been used here to control the size of protoplasts of the marine alga Bryopsis plumosa. The Figure shows protoplasts prepared on a 20 μm pitch TiO2 template, illustrating the small range of diameters that are obtained. This technique serves as a convenient way to provide cell models for in vitro physiological studies.

    7. Nanostructured Hybrid Organic–Inorganic Lanthanide Complex Films Produced In Situ via a Sol-Gel Approach (pages 646–649)

      D. Dong, S. Jiang, Y. Men, X. Ji and B. Jiang

      Version of Record online: 17 APR 2000 | DOI: 10.1002/(SICI)1521-4095(200005)12:9<646::AID-ADMA646>3.0.CO;2-W

      Nanostructural hybrid organic–inorganic lanthanide complex films were prepared in situ by use of a novel sol-gel precursor containing pendant triethoxysilyl and carboxyl groups (see Figure). The resulting transparent and crack-free films gave rise to strong red or green emission, even at low lanthanide ion concentration. Phase separation and lanthanide ion aggregation were controlled at the nanoscale.

    8. Gelation by Acrylamide, a Quasi-Universal Medium for the Synthesis of Fine Oxide Powders for Electroceramic Applications (pages 649–652)

      A. Sin and P. Odier

      Version of Record online: 17 APR 2000 | DOI: 10.1002/(SICI)1521-4095(200005)12:9<649::AID-ADMA649>3.0.CO;2-K

      The synthesis of fine powders of electroceramic oxides (e.g., superconductors, dielectrics, and materials exhibiting colossal magnetoresistance) is most commonly carried out by solid-state reaction. Wet chemical methods, which overcome some disadvantages of the solid-state route, are often difficult to scale up. The improved acrylamide sol-gel process presented here is shown to be a fast, cheap, reproducible, and easily scaled-up route to fine oxide powders. The synthesis of La2CuNiO6, which cannot be obtained by solid-state reaction at ambient pressure, demonstrates the potential of this method in the search for new materials.

    9. Tuning the Photonic Bandgap Properties of Crystalline Arrays of Polystyrene Beads by Annealing at Elevated Temperatures (pages 653–656)

      B. Gates, S. H. Park and Y. Xia

      Version of Record online: 17 APR 2000 | DOI: 10.1002/(SICI)1521-4095(200005)12:9<653::AID-ADMA653>3.0.CO;2-3

      A 3D photonic crystal that operates in the visible regime is presented. The bandgap properties of this photonic crystal, fabricated from ∼230 nm polystyrene beads, can be tuned in a controllable way by annealing the sample at elevated temperatures (see Figure). It is demonstrated that shrinkage and a change in the shape of the beads are responsible for the change in bandgap properties.

    10. Gas-Sensitive Properties of Nitrogen-Rich Carbon Nitride Films (pages 656–660)

      L. M. Zambov, C. Popov, N. Abedinov, M. F. Plass, W. Kulisch, T. Gotszalk, P. Grabiec, I. W. Rangelow and R. Kassing

      Version of Record online: 17 APR 2000 | DOI: 10.1002/(SICI)1521-4095(200005)12:9<656::AID-ADMA656>3.0.CO;2-S

      Electronic noses based on polymer-like carbon nitride (CNx) are investigated by these authors. The gas-sensing properties of CNx are examined, focusing on the detection of humidity and ammonia. Two basic types of gas sensor—capacitance and microelectromechanical (see Figure)—are discussed. It is found that the sensors are highly sensitive, stable, and have short response and recovery times.

    11. First TOF Donors: Synthesis and Characterization of Dibenzo- and Dinaphthotetraoxafulvalenes (pages 661–664)

      K. Tanaka, K. Yoshida, T. Ishida, A. Kobayashi and T. Nogami

      Version of Record online: 17 APR 2000 | DOI: 10.1002/(SICI)1521-4095(200005)12:9<661::AID-ADMA661>3.0.CO;2-7

      Synthetic metals based on tetrachalcogenafulvalene donor molecules have received much attention. Unlike the thia-, selena-, and tellura-derivatives, tetraoxafulvalenes (TOFs) are rare, because of difficulties in their preparation and isolation. Here is presented the first unequivocal synthesis, spectral characterization, and X-ray structure determination of TOF derivatives—dibenzo- (see Figure) and dinaphtho-TOF.

    12. Desolvation Mechanism of Crystalline Host–Guest Compounds Considering Pseudopolymorphism: Study of the 1,1′-Binaphthyl-2,2′-Dicarboxylic Acid Clathrates with DMF (pages 664–667)

      K. Beketov, E. Weber, B. T. Ibragimov, J. Seidel and K. Köhnke

      Version of Record online: 17 APR 2000 | DOI: 10.1002/(SICI)1521-4095(200005)12:9<664::AID-ADMA664>3.0.CO;2-W

      Inclusion compounds have significant potential as chemical receptors for sensors; however, it is necessary to understand the encapsulation and release processes for such applications. These authors have utilized the powerful combination of simultaneous thermogravimetry and differential scanning calorimetry and X-ray diffraction to study the decomposition mechanism of the clathrates between 1,1′-binaphthyl-2,2′-dicarboxylic acid (BNDA) and dimethyl formamide (DMF). Decomposition was found to proceed via three intermediate phases whose structures were determined by single crystal X-ray crystallography.

    13. Starburst Molecules Based on Hexathienylbenzene Units: Potential Hole-Transport Materials (pages 668–669)

      I.-Y. Wu, J. T. Lin, Y.-T. Tao and E. Balasubramaniam

      Version of Record online: 17 APR 2000 | DOI: 10.1002/(SICI)1521-4095(200005)12:9<668::AID-ADMA668>3.0.CO;2-G

      Starburst amorphous compounds as hole-transporting materials in light-emitting devices are investigated here. In addition, the synthesis by Stille's palladium-catalyzed cross-coupling reaction (see Figure) of these compounds—benzene molecules with six peripheral diarylthienylamine moieties—is reported as are their physical and electrochemical properties.

    14. Conducting Polymer-Coated Latex Particles (pages 671–674)

      M. A. Khan and S. P. Armes

      Version of Record online: 17 APR 2000 | DOI: 10.1002/(SICI)1521-4095(200005)12:9<671::AID-ADMA671>3.0.CO;2-3

      Coating sterically stabilized latex particles with an ultrathin overlayer of conducting polymer—core–shell particles (see Figure)—is a very effective way to form stable colloidal dispersions of particles with useful electrical properties. Recent developments in this field are presented here, including their use as micro-projectiles in hypervelocity impact experiments in order to model the behavior of micro-meteorites—cosmic dust.

    15. New (Inter)Faces: Polymers and Inorganic Materials (pages 675–681)

      M. J. MacLachlan, I. Manners and G. A. Ozin

      Version of Record online: 17 APR 2000 | DOI: 10.1002/(SICI)1521-095(200005)12:9<675::AID-DMA675>3.0.CO;2-

      The recent flurry of research activity at the boundary of inorganic and polymer chemistry reflects the significant potential for the development of new materials with interesting functions, such as shaped magnetic ceramics from crosslinked poly(ferrocenylsilane)s (see Figure). This research news article discusses concepts and highlights from the recent literature.