Advanced Materials

Cover image for Advanced Materials

November, 2004

Volume 16, Issue 22

Pages 1975–2070

    1. Physicochemical Properties of Surface-Initiated Polymer Films in the Modification and Processing of Materials (pages 1983–1994)

      G. K. Jennings and E. L. Brantley

      Article first published online: 9 DEC 2004 | DOI: 10.1002/adma.200400810

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      The physicochemical aspects of surface-initiated polymer films used to modify planar and non-planar surfaces and to produce micro- and nanoscale patterned features (see Figure) are reviewed. Recent advances in the use of responsive polymer films and uses of surface-initiated polymer films to modify materials properties and impact applications in chromatography, nanoparticle-templated synthesis, and carbon nanotube dispersion are highlighted.

    2. Preparation of Microfluidic Devices Using Micropatterning of a Photosensitive Material by a Maskless, Liquid-Crystal-Display Projection Method (pages 1997–2001)

      J. Kobayashi, M. Yamato, K. Itoga, A. Kikuchi and T. Okano

      Article first published online: 9 DEC 2004 | DOI: 10.1002/adma.200400312

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      An all-in-one device for fabricating microfluidic devices is developed by modifying a commercially available liquid-crystal-display projector. Micropatterns are formed on photosensitive materials from images that are prepared using personal-computer software. Desired poly(dimethylsiloxane) microfluidic channels (see Figure) are obtained rapidly without the need for expensive photomasks and light sources.

    3. Effective Color Tuning in Organic Light-Emitting Diodes Based on Aluminum Tris(5-aryl-8-hydroxyquinoline) Complexes (pages 2001–2003)

      V. A. Montes, G. Li, R. Pohl, J. Shinar and P. Anzenbacher Jr.

      Article first published online: 9 DEC 2004 | DOI: 10.1002/adma.200401155

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      Tris(quinolate)AlIII (Alq3)-based metallocomplexes with electron- deficient or electron-rich aryl substituents display remarkable blue-to-red tuning of both photo- and electroluminescence, covering most of the visible-light region (see Figure). The correlation between the electronic properties of the aryl substituents, highest occupied–lowest unoccupied molecular orbital (HOMO–LUMO) gap, and the emissive properties of the complexes suggests this approach may be used to design new light-emitting materials.

    4. First Examples of Alkenyl Pyridines as Organic Ligands for Phosphorescent Iridium Complexes (pages 2003–2007)

      B. M. J. S. Paulose, D. K. Rayabarapu, J.-P. Duan and C.-H. Cheng

      Article first published online: 11 OCT 2004 | DOI: 10.1002/adma.200400149

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      The first successful synthesis of iridium complexes {(PEP)2Ir(acac), (NEP)2Ir(acac), (PETP)2Ir(acac), (MPEP)2Ir(acac), and (PP)2Ir(acac)} (see Figure) using an olefin-tethered pyridine ring is described. The electroluminescent devices prepared using these iridium complexes as dopant emitters showed very high brightness and efficiencies.

    5. Biodegradable Microfluidics (pages 2007–2012)

      K. R. King, C. C. J. Wang, M. R. Kaazempur-Mofrad, J. P. Vacanti and J. T. Borenstein

      Article first published online: 9 DEC 2004 | DOI: 10.1002/adma.200306522

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      A biodegradable microfabrication platform for constructing 3D high- resolution devices for tissue engineering and drug delivery is presented. Biodegradable polymer films with built-in micrometer-scale features are stacked and fusion bonded to construct fully biodegradable, poly(DL-lactic-co-glycolide) (PLGA)-based, monolithic, multilayer, microfluidic networks. Integration with cells or drug compounds will enable use of these devices in therapeutic applications (scale bar: ∼ 300 μm).

    6. Self-Assembly of the Mesoporous Electrode Material Li3Fe2(PO4)3 Using a Cationic Surfactant as the Template (pages 2012–2017)

      S. Zhu, H. Zhou, T. Miyoshi, M. Hibino, I. Honma and M. Ichihara

      Article first published online: 9 DEC 2004 | DOI: 10.1002/adma.200400207

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      Mesoporous Li3Fe2(PO4)3 battery electrode materials (see Figure) with a discharge capacity of 140 mAh g–1 at 20 mA g–1 self-assemble under aqueous conditions using a cationic surfactant as the template. Mössbauer spectroscopy results are characteristic of Fe3+ ions in oxides, while the interaction of lithium with Fe and O in mesoporous Li3Fe2-(PO4)3 is verified by 7Li NMR. This synthetic strategy may be applied to the production of other multi-metal phosphate ordered mesoporous structures.

    7. Crystalline Thin Films Formed by Supramolecular Assembly for Ultrahigh-Density Data Storage (pages 2018–2021)

      Y. Q. Wen, Y. L. Song, G. Y. Jiang, D. B. Zhao, K. Ding, W. F. Yuan, X. Lin, H. J. Gao, L. Jiang and D. B. Zhu

      Article first published online: 9 DEC 2004 | DOI: 10.1002/adma.200400543

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      Crystalline organic films formed by self-assembly of 2,2-dimethyl-α,α,α′,α′-tetraphenyldioxolane-4,5-dimethanol and coumarin molecules can be used for ultrahigh-density data storage. A 3 × 4 matrix pattern (see Figure) was recorded by applying voltage pulses between a scanning tunneling microscope tip and the film. Regulating the amplitude and width of the applied pulsed voltage allows a data storage density of about 1013 bits cm–2 to be achieved.

    8. Novel Micro/Nanoscale Hybrid Reinforcement: Multiwalled Carbon Nanotubes on SiC Particles (pages 2021–2024)

      L. Ci and J. Bai

      Article first published online: 9 DEC 2004 | DOI: 10.1002/adma.200400379

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      SiC particles are coated with multi-walled carbon nanotubes using a simple chemical vapor deposition process. This new type of micro/nanoscale hybrid reinforcement combines the characteristics of carbon nanotubes and the micrometer-sized SiC particles. Using this hybrid reinforcement in an epoxy composite produced a significant improvement in mechanical properties, attributed to the carbon-nanotube- reinforced interface between the epoxy matrix and the particles.

    9. A New Approach to the Electrochemical Metallization of Organic Monolayers: Palladium Deposition onto a 4,4′-Dithiodipyridine Self-Assembled Monolayer (pages 2024–2028)

      T. Baunach, V. Ivanova, D. M. Kolb, H.-G. Boyen, P. Ziemann, M. Büttner and P. Oelhafen

      Article first published online: 9 DEC 2004 | DOI: 10.1002/adma.200400409

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      Depositing metal layers onto a self-assembled monolayer (SAM) is achieved using a new technique. Au(111) bearing a 4,4′-dithiodipyridine SAM is immersed into a PdII solution without potential control, causing PdII to adsorb on the surface by forming a complex with the pyridine species. The PdII ions are then electrochemically reduced to Pd0 (see Figure). Angle-resolved X-ray photoelectron spectroscopy measurements unequivocally show that the reduced Pd resides on top of the SAM.

    10. Enhanced Field Emission of ZnO Nanowires (pages 2028–2032)

      D. Banerjee, S. H. Jo and Z. F. Ren

      Article first published online: 9 DEC 2004 | DOI: 10.1002/adma.200400629

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      Enhanced field emission from ZnO nanowires grown on carbon cloth (see Figure) has been measured. These emitters produced a field emission current density of 1 mA cm–2 at about 0.7 V μm–1, corresponding to an exceptionally high field-enhancement factor of 4.11 × 104. Such an extremely high field-enhancement factor is believed to be the combined effect of the high aspect ratio of ZnO nanowires and the geometry of the carbon-cloth substrate.

    11. Bistriarylamine Polymer-Based Composites for Photorefractive Applications (pages 2032–2036)

      J. Thomas, C. Fuentes-Hernandez, M. Yamamoto, K. Cammack, K. Matsumoto, G. A. Walker, S. Barlow, B. Kippelen, G. Meredith, S. R. Marder and N. Peyghambarian

      Article first published online: 9 DEC 2004 | DOI: 10.1002/adma.200400102

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      The development and performance of tetraphenyldiaminobiphenyl-based polymer composites with stable video-rate-compatible response times over large exposures is reported (see Figure). The high diffraction efficiency together with an exposure-history independence of the response time described is a significant advance for developing an all-organic photorefractive composite for device applications.

    12. Carbon-Nanotube-Reinforced Polymer-Derived Ceramic Composites (pages 2036–2040)

      L. An, W. Xu, S. Rajagopalan, C. Wang, H. Wang, Y. Fan, L. Zhang, D. Jiang, J. Kapat, L. Chow, B. Guo, J. Liang and R. Vaidyanathan

      Article first published online: 9 DEC 2004 | DOI: 10.1002/adma.200306241

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      Fully dense ceramic–carbon-nanotube composites with homogeneously distributed multiwalled carbon nanotubes (MWCNTs) (see Figure; inset shows a single MWCNT) have been synthesized by a unique method, which uses a polymer-derived ceramic as the composite matrix. Composites with an MWCNT fraction of 6.4 vol.-% had significantly increased Young's moduli, hardness, and damage resistance, compared to the values for the pure ceramic matrix.

    13. High-Efficiency Soft-Contact-Laminated Polymer Light-Emitting Devices with Patterned Electrodes (pages 2040–2045)

      T.-W. Lee, J. Zaumseil, S. H. Kim and J. W. P. Hsu

      Article first published online: 9 DEC 2004 | DOI: 10.1002/adma.200400182

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      Organic light-emitting devices (OLEDs) formed by soft-contact lamination (ScL) show high luminous efficiency (∼ 2.25 cd A–1 with a Au electrode) and better operational stability than similar devices fabricated by thermal evaporation. The laminated electrodes consist of thin films of Au supported by flat or structured elastomeric elements of polydimethylsiloxane. By combining ScL and soft lithography, it is possible to fabricate high-efficiency OLEDs with micrometer-scale light-emitting areas.

    14. High Efficiency Fine Particulate Filtration Using Carbon Nanotube Coatings (pages 2045–2049)

      G. Viswanathan, D. B. Kane and P. J. Lipowicz

      Article first published online: 9 DEC 2004 | DOI: 10.1002/adma.200400463

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      Thin films of multiwalled carbon nanotubes (MWNTs) deposited on cellulose fiber filters (see Figure) are evaluated as particulate filtration media. Even for very low MWNT coverages (∼0.07 mg cm–2), these filters exhibit efficiencies greater than 99 % for airborne fine particles. The pore structure and quality of the nanotube-based filters have also been characterized.

    15. Nanoelectronic Carbon Dioxide Sensors (pages 2049–2052)

      A. Star, T.-R. Han, V. Joshi, J.-C. P. Gabriel and G. Grüner

      Article first published online: 29 OCT 2004 | DOI: 10.1002/adma.200400322

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      Carbon nanotube field-effect transistors (NTFETs) coated with poly(ethyleneimine) (PEI) and starch polymers exhibit electrical conductance changes upon exposure to CO2 gas in air at ambient temperature (see Figure). This observation has furnished nanoelectronic CO2 sensors. Their small size and low power consumption has enormous potential in wireless sensing for industrial and medical CO2 sensor units.

    16. Template-Assisted Fabrication of Dense, Aligned Arrays of Titania Nanotubes with Well-Controlled Dimensions on Substrates (pages 2052–2057)

      M. S. Sander, M. J. Côté, W. Gu, B. M. Kile and C. P. Tripp

      Article first published online: 9 DEC 2004 | DOI: 10.1002/adma.200400446

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      Dense arrays of vertically aligned titania nanotubes (see Figure) are created directly on silicon substrates by combining atomic layer deposition with an alumina template-based fabrication approach. This method enables excellent control over the nanotube dimensions, including their wall thickness, diameter, and height. Nanotubes were fabricated with tube walls thin enough (< 3 nm) to exhibit a wall-thickness- dependent blue-shift in the optical absorption spectra of the arrays.

    17. Synthesis of Ordered, Uniform, Macroporous Carbons with Mesoporous Walls Templated by Aggregates of Polystyrene Spheres and Silica Particles for Use as Catalyst Supports in Direct Methanol Fuel Cells (pages 2057–2061)

      G. S. Chai, I. S. Shin and J.-S. Yu

      Article first published online: 9 DEC 2004 | DOI: 10.1002/adma.200400283

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      Porous carbons with mesoporous walls (see Figure) are produced by template replication of aggregates of small silica particles, which were themselves templated by a self-assembled lattice of larger monodisperse polystyrene spheres. A direct methanol fuel cell using the new material as a catalyst support shows significantly improved performance due to the combination of high surface area and facile fuel and product diffusion.

    18. Nanofibers of Conjugated Polymers Prepared by Electrospinning with a Two-Capillary Spinneret (pages 2062–2066)

      D. Li, A. Babel, S. A. Jenekhe and Y. Xia

      Article first published online: 20 OCT 2004 | DOI: 10.1002/adma.200400606

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      Uniform nanofibers composed of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] and its blends with poly(3-hexylthiophene) are formed by co-electrospinning their solutions with poly(vinyl pyrrolidone) (PVP) through a coaxial capillary system, followed by extraction of the PVP phase (see Figure). Compared with spin-cast films, the fibers show reduced phase separation and improved energy-transfer efficiency.