Advanced Materials

Cover image for Vol. 18 Issue 5

March, 2006

Volume 18, Issue 5

Pages 535–674

    1. Cover Picture: A Micropatterned Hydrogel Platform for Chemical Synthesis and Biological Analysis (Adv. Mater. 5/2006)

      M. Zourob, J. E. Gough and R. V. Ulijn

      Article first published online: 2 MAR 2006 | DOI: 10.1002/adma.200690022

      A polymer hydrogel platform for peptide arrays compatible both with solid-phase peptide synthesis (SPPS) conditions and the aqueous environment essential for biological assays is demonstrated. Micropatterning followed by multiple-step peptide synthesis in situ is followed by proof-of-concept on-chip biological assays involving cells and enzymes (see Figure and cover).

    2. Contents: Adv. Mater. 5/2006 (pages 535–543)

      Article first published online: 2 MAR 2006 | DOI: 10.1002/adma.200690019

    3. You have free access to this content
      Enzymatic Formation of Supramolecular Hydrogels (page 545)

      Z. Yang, H. Gu, D. Fu, P. Gao, J. K. Lam and B. Xu

      Article first published online: 2 MAR 2006 | DOI: 10.1002/adma.200690020

      This article corrects:

      Enzymatic Formation of Supramolecular Hydrogels

      Vol. 16, Issue 16, 1440–1444, Article first published online: 2 SEP 2004

    4. Site-Selective Functionalization of Carbon Nanotubes (pages 547–552)

      M. S. Raghuveer, A. Kumar, M. J. Frederick, G. P. Louie, P. G. Ganesan and G. Ramanath

      Article first published online: 27 JAN 2006 | DOI: 10.1002/adma.200500181

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      Site-selective functionalization of nano- or macroscopic segments of carbon nanotubes is accomplished using focused ion beams followed by site-selective derivatization of the segments with nanostructures and biomolecules (see Figure). Such hybrid nanostructures open up new possibilities for nanoscale addressing, fingerprinting, recognition, and separation.

    5. Field-Emission Behavior of a Carbon-Nanotube-Implanted Co Nanocomposite Fabricated from Pearl-Necklace-Structured Carbon Nanotube/Co Powders (pages 553–558)

      S. I. Cha, K. T. Kim, S. N. Arshad, C. B. Mo, K. H. Lee and S. H. Hong

      Article first published online: 2 MAR 2006 | DOI: 10.1002/adma.200501267

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      Pearl-necklace-structured CNT/Co nanocomposite powders, with spherical Co nanoparticles threaded by penetrating CNTs, have been fabricated using a molecular process. The nanocomposite powders have been screen-printed and sintered into CNT-implanted Co nanocomposite emitters, with the CNTs standing upright on the surface of the substrate. The CNT-implanted Co nanocomposite emitters show outstanding field-emission behavior, including a low turn-on electric field and high current density.

    6. Towards High-Throughput Production of Uniformly Encoded Microparticles (pages 559–564)

      L. Martín-Banderas, A. Rodríguez-Gil, Á. Cebolla, S. Chávez, T. Berdún-Álvarez, J. M. Fernandez Garcia, M. Flores-Mosquera and A. M. Gañán-Calvo

      Article first published online: 2 MAR 2006 | DOI: 10.1002/adma.200501976

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      Flow-focusing technology: The straightforward, fast production of microparticles of a controlled size (a few micrometers, see Figure) using the combination of a flow-focusing device and a solvent extraction/evaporation process is shown. This strategy relies on the design of microscale systems that possess a high input energy efficiency.

    7. Out-of-Equilibrium Self-Assembly of Binary Mixtures of Nanoparticles (pages 565–571)

      C. G. Sztrum and E. Rabani

      Article first published online: 27 JAN 2006 | DOI: 10.1002/adma.200501408

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      A coarse-grained lattice-gas model is developed to study the drying-mediated self-assembly of binary mixtures of nanoparticles (NPs). Three model systems are considered, corresponding to equilibrium phase separation between two NPs (A and B), to an amorphous state, and to an ordered, checkerboard-like superstructure (see Figure; red: NPA; green: NPB; blue: solvent). The mechanism for self-ordering depends on the nature of the equilibrium superstructure and on the dynamic coupling to the evaporating solvent.

    8. New Architecture for High-Efficiency Polymer Photovoltaic Cells Using Solution-Based Titanium Oxide as an Optical Spacer (pages 572–576)

      J. Y. Kim, S. H. Kim, H.-H. Lee, K. Lee, W. Ma, X. Gong and A. J. Heeger

      Article first published online: 2 MAR 2006 | DOI: 10.1002/adma.200501825

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      Polymer photovoltaic cells with power conversion efficiencies approaching 5 % have been fabricated using titanium oxide (TiOx) as an optical spacer (see Figure). Solar cells with a TiOx layer (deposited via a sol–gel process) between the active layer and the electron-collecting aluminum electrode exhibit approximately a 50 % enhancement in short-circuit current compared to similar devices without the optical spacer, as a result of modification of the spatial distribution of the light intensity inside the device.

    9. Electrically Controlled Drug Delivery from Biotin-Doped Conductive Polypyrrole (pages 577–581)

      P. M. George, D. A. LaVan, J. A. Burdick, C.-Y. Chen, E. Liang and R. Langer

      Article first published online: 2 MAR 2006 | DOI: 10.1002/adma.200501242

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      A platform for controlled drug delivery using a conductive-polymer substrate has been created. Through the incorporation of biotin into the conductive polymer polypyrrole (PPy) and the subsequent attachment of the desired drug molecule (such as nerve growth factor, NGF) via a streptavidin linker, an applied potential can trigger release of the drug from the polymer surface (see figure).

    10. Surface-Functionalized Polymer Nanoparticles for Selective Sequestering of Heavy Metals (pages 582–586)

      C. A. Bell, S. V. Smith, M. R. Whittaker, A. K. Whittaker, L. R. Gahan and M. J. Monteiro

      Article first published online: 2 FEB 2006 | DOI: 10.1002/adma.200501712

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      Xanthate-mediated (reversible addition-fragmentation chain transfer) emulsion polymerization has been used to create novel polystyrene nanoparticles with functionalized surfaces (see Figure) for the selective sequestering of heavy metals from water below ppm levels. These nanoparticles show a high degree of selectivity for HgII over CoII. This technology has potential for the selective remediation of heavy metals from the human blood system.

    11. Multiwalled Carbon Nanotubes Beaded with ZnO Nanoparticles for Ultrafast Nonlinear Optical Switching (pages 587–592)

      Y. Zhu, H. I. Elim, Y.-L. Foo, T. Yu, Y. Liu, W. Ji, J.-Y. Lee, Z. Shen, A. T. S. Wee, J. T. L. Thong and C. H. Sow

      Article first published online: 2 MAR 2006 | DOI: 10.1002/adma.200501918

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      A hybrid system of ZnO nanoparticles on multiwalled carbon nanotubes (MWNTs) is fabricated by simply heating Zn-coated MWNTs on a hot plate in air. Ultrafast optical switching and three-photon adsorption are observed from this hybrid system, and the absorption coefficient can be readily adjusted by changing the Zn-coating thickness. These results provide opportunities for cost-effectively integrating carbon nanotubes with functional oxide nanoparticles in future nanodevices.

    12. Control of Morphology and Helicity of Chiral Mesoporous Silica (pages 593–596)

      H. Jin, Z. Liu, T. Ohsuna, O. Terasaki, Y. Inoue, K. Sakamoto, T. Nakanishi, K. Ariga and S. Che

      Article first published online: 27 JAN 2006 | DOI: 10.1002/adma.200502038

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      Chiral ordered mesoporous silica has been synthesized by using a chiral surfactant (N-myristoyl-L-alanine sodium salt) as a template, 3-aminopropyltriethoxysilane as a co-structure directing agent, and tetraethoxylsilane as an inorganic source. The helicity and the morphology of the mesoporous silica are determined by the stirring rate during the chiral surfactant self-assembly (see Figure), providing new insight into the chiral self-assembly of molecules.

    13. Pattern Registration Between Spherical Block-Copolymer Domains and Topographical Templates (pages 597–601)

      J. Y. Cheng, F. Zhang, H. I. Smith, G. J. Vancso and C. A. Ross

      Article first published online: 31 JAN 2006 | DOI: 10.1002/adma.200501936

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      Pattern registration is achieved in thin films of self-assembling block copolymers by using a topographical template to guide the positions of the polymer domains. The placement accuracy of the polymer domains is related to the edge roughness of the topographical template, and the ultimate placement accuracy is assessed (see Figure). For a block copolymer with spherical morphology, a registered polymer array is achieved by using a two-dimensional template.

    14. Dipolar Dibenzothiophene S,S-Dioxide Derivatives Containing Diarylamine: Materials for Single-Layer Organic Light-Emitting Devices (pages 602–606)

      T.-H. Huang, J. T. Lin, L.-Y. Chen, Y.-T. Lin and C.-C. Wu

      Article first published online: 2 MAR 2006 | DOI: 10.1002/adma.200502078

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      Dipolar compounds for use in simplified, single-layer organic light-emitting devices (OLEDs) containing a dibenzothiophene S,S-dioxide core and two peripheral diarylamines are synthesized. These materials exhibit bipolar carrier-transport properties, and efficient single-layer electroluminescent devices (see Figure; ITO: indium tin oxide) using these materials are demonstrated. These compounds may lead to devices with performances comparable to multilayer ones at lower costs.

    15. Alignment Control of a Columnar Liquid Crystal for a Uniformly Homeotropic Domain Using Circularly Polarized Infrared Irradiation (pages 607–610)

      H. Monobe, K. Awazu and Y. Shimizu

      Article first published online: 27 JAN 2006 | DOI: 10.1002/adma.200501762

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      Circularly polarized infrared irradiation of a hexagonal columnar mesophase with a free-electron laser causes the liquid crystal to change from an “edge-on” alignment to a uniformly homeotropic “face-on” alignment (see Figure) due to vibrational excitation of the aromatic C–H vibration band of triphenylene.

    16. Nanostructured Hydrogels for Three-Dimensional Cell Culture Through Self-Assembly of Fluorenylmethoxycarbonyl–Dipeptides (pages 611–614)

      V. Jayawarna, M. Ali, T. A. Jowitt, A. F. Miller, A. Saiani, J. E. Gough and R. V. Ulijn

      Article first published online: 2 MAR 2006 | DOI: 10.1002/adma.200501522

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      A number of short peptide amphiphiles consisting of dipeptides linked to fluorenylmethoxycarbonyl spontaneously form fibrous hydrogels under physiological conditions (see figure). The structural and physical properties of these gels are dictated by the amino acid sequence of the peptide building blocks, and the gels support the three-dimensional cell culture of chondrocytes.

    17. Synthesis of La9.33Si6O26 Pore–Solid Nanoarchitectures via Epoxide-Driven Sol–Gel Chemistry (pages 615–618)

      S. Célérier, C. Laberty-Robert, J. W. Long, K. A. Pettigrew, R. M. Stroud, D. R. Rolison, F. Ansart and P. Stevens

      Article first published online: 2 MAR 2006 | DOI: 10.1002/adma.200501938

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      A sol–gel-based strategy for the production of mesoporous, nanostructured, single-phase La9.33Si6O26 apatite in an aerogel-type framework is reported (see Figure). The crystallization temperature of these nanoarchitectures is low (800 °C), thus preventing detrimental particle growth. This morphology allows sintering to dense ceramics at lower temperatures relative to other nanocrystalline forms, which is advantageous for the application of these materials as electrolytes in solid-oxide fuel cells.

    18. Alumina-Template Synthesis of Fluorescent RuO2 Nanotubes Derived from Ru3(CO)12 Clusters (pages 619–623)

      H. Tan, E. Ye and W. Y. Fan

      Article first published online: 2 MAR 2006 | DOI: 10.1002/adma.200501356

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      RuO2 nanotubes with diameters of 15–25 nm and up to 3 μm in length have been prepared by the thermal decomposition of Ru3(CO)12 inside alumina templates. The RuO2 (110) planes grow along the long axis of the straight crystalline nanotubes. The growth of these fluorescent nanotubes appears to have proceeded via mononuclear ruthenium carbonyl intermediates (see Figure).

    19. Giant Thermal Tunability of the Lamellar Spacing in Block-Copolymer-Like Supramolecules Formed from Binary-End-Functionalized Polymer Blends (pages 624–629)

      J. Huh, H. J. Park, K. H. Kim, K. H. Kim, C. Park and W. H. Jo

      Article first published online: 2 MAR 2006 | DOI: 10.1002/adma.200500963

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      Block-copolymer-like supramolecules (see Figure) permit thermal tuning of the microphase period due to reversible supramolecular assembly and disassembly. The supramolecular system based on a binary end-functionalized blend forming diblock- and triblock-like supramolecules shows that the lamellar microphase upon heating swells up to almost 300%. Such effective temperature tunability of the microphase period may find a variety of uses in applications that require patterning over large dimensions.

    20. Fabrication of Hydrogen-Permeable Composite Membranes Packed with Palladium Nanoparticles (pages 630–632)

      D. A. Pacheco Tanaka, M. A. Llosa Tanco, T. Nagase, J. Okazaki, Y. Wakui, F. Mizukami and T. M. Suzuki

      Article first published online: 2 MAR 2006 | DOI: 10.1002/adma.200501900

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      Novel Pd membrane: A composite palladium membrane for hydrogen separation has been fabricated by vacuum-assisted electroless plating. Nanometer-sized palladium grains are packed into a mesoporous γ-alumina layer located on a macroporous alumina tubular support (see figure). The observed high resistance to hydrogen embrittlement is attributed to the novel membrane configuration and to size-related effects of the palladium grains, and these materials may find use in gas-separation membranes.

    21. Metal-Induced Seeding of Macropore Arrays in Silicon (pages 633–636)

      S. Koynov, M. S. Brandt and M. Stutzmann

      Article first published online: 2 MAR 2006 | DOI: 10.1002/adma.200501179

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      Ordered seed arrays for electrochemical macropore formation can be prepared on silicon surfaces by metal-induced seeding (MIS). A laser interference pattern on an Au-coated Si surface is transferred into a lattice of AuSi eutectic dots during a single intense laser pulse and subsequently developed into spherical pits by Au etching. A substantial advantage of MIS is the possibility to obtain seeding on receded surfaces (see Figure), allowing the incorporation of arrays of microchannels into three-dimensional structures.

    22. Carbon-Nanotube-Reinforced Polyaniline Fibers for High-Strength Artificial Muscles (pages 637–640)

      G. M. Spinks, V. Mottaghitalab, M. Bahrami-Samani, P. G. Whitten and G. G. Wallace

      Article first published online: 2 MAR 2006 | DOI: 10.1002/adma.200502366

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      Carbon-nanotube-reinforced polyaniline fibers (see Figure) possess improved breaking strength and higher operating stress levels than neat polyaniline, potentially allowing generation of larger stresses by electrochemical actuators containing these fibers. The fibers have tensile strengths of 255 MPa and operate to stress levels in excess of 100 MPa, three times higher than previously reported for conducting-polymer actuators.

    23. Silica-Incorporated Polyelectrolyte-Complex Fibers as Tissue-Engineering Scaffolds (pages 641–644)

      A. C. A. Wan, B. C. U. Tai, K.-J. Leck and J. Y. Ying

      Article first published online: 2 MAR 2006 | DOI: 10.1002/adma.200502096

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      Fibers of polyelectrolyte complexes incorporated in silica are synthesized by combining the polymerization of hydrolyzed tetraethylorthosilicate with the process of interfacial polyelectrolyte complexation. The resulting fibers are hydro-entangled to successfully produce porous scaffolds that act as a platform for the immobilization of biological molecules for tissue engineering (see Figure).

    24. Highly Reversible Lithium Storage in Porous SnO2 Nanotubes with Coaxially Grown Carbon Nanotube Overlayers (pages 645–649)

      Y. Wang, H. C. Zeng and J. Y. Lee

      Article first published online: 2 MAR 2006 | DOI: 10.1002/adma.200501883

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      The preparation of SnO2 nanotubes with coaxially grown carbon nanotube overlayers with good conformal control of shape and size is reported. The SnO2-core/carbon-shell nanotubes (see Figure) are excellent reversible lithium-ion storage compounds combining the best features of carbon (for cyclability) and SnO2 (for capacity). These structures deliver high specific capacity (∼ 540–600 mA h g–1) and good cyclability (0.0375% capacity loss per cycle).

    25. Aligned AlN Nanorods with Multi-tipped Surfaces—Growth, Field-Emission, and Cathodoluminescence Properties (pages 650–654)

      J. H. He, R. S. Yang, Y. L. Chueh, L. J. Chou, L. J. Chen and Z. L. Wang

      Article first published online: 2 MAR 2006 | DOI: 10.1002/adma.200501803

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      Well-aligned aluminum nitride nanorods with hairy surfaces (see Figure) are a new hierarchical nanostructure with promising field-emission properties. The columnar nanostructures are produced by a vapor–solid process. Their cathodoluminescence spectrum reveals an intense emission peak with a low turn-on field of 3.8 V μm–1, suggesting potential applications in optoelectronic nanodevices.

    26. A Micropatterned Hydrogel Platform for Chemical Synthesis and Biological Analysis (pages 655–659)

      M. Zourob, J. E. Gough and R. V. Ulijn

      Article first published online: 2 FEB 2006 | DOI: 10.1002/adma.200501840

      Thumbnail image of graphical abstract

      A polymer hydrogel platform for peptide arrays compatible both with solid-phase peptide synthesis (SPPS) conditions and the aqueous environment essential for biological assays is demonstrated. Micropatterning followed by multiple-step peptide synthesis in situ is followed by proof-of-concept on-chip biological assays involving cells and enzymes (see Figure and cover).

    27. Electric-Field-Controlled Surface Instabilities in Soft Elastic Films (pages 660–663)

      N. Arun, A. Sharma, V. B. Shenoy and K. S. Narayan

      Article first published online: 6 FEB 2006 | DOI: 10.1002/adma.200502199

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      The surfaces of soft elastic films spontaneously form patterns. Application of an electric field above a critical value (φcric) to these patterns produces adhesive zones with distinct morphologies, such as pillars, large-amplitude fingers, or complete intimate contact (see Figure). These morphology changes, governed by film parameters such as stiffness and thickness, are explained by the physics of electrostatic-field-induced contact instabilities.

    28. Unique Properties of Selectively Formed Zirconia Nanostructures (pages 664–667)

      J. L. Gole, S. M. Prokes, J. D. Stout, O. J. Glembocki and R. Yang

      Article first published online: 2 MAR 2006 | DOI: 10.1002/adma.200500769

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      Hollow ZrO2 nanoshells are formed over a precise range of temperature and pressure from the oxidation of ZrCl2. The greatly enhanced photoluminescence (∼ 110×) that the nanoshells exhibit compared to that of either nanospheres or irregularly shaped nanoparticles is attributed to the nanoshell geometry (see Figure). Potential future applications include information-storage devices.

    29. High-Strength Mats from Electrospun Poly(p-Phenylene Biphenyltetracarboximide) Nanofibers (pages 668–671)

      C. Huang, S. Chen, D. H. Reneker, C. Lai and H. Hou

      Article first published online: 2 MAR 2006 | DOI: 10.1002/adma.200501806

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      High-strength polyimide mats have been formed from electrospun nanofibers of a rigid-rod-like poly(p-phenylene biphenyltetracarboximide) (see Figure). Non-woven mats of aligned nanofibers have a tensile strength of 664 MPa and a tensile modulus of 15.3 GPa. These high-performance electrospun nanofibers with excellent mechanical properties and heat resistance are expected to be useful for applications such as protective clothing and heat-resistant filters.

    30. Author Index and Subject Index Adv. Mater. 5/2006 (pages 673–674)

      Article first published online: 2 MAR 2006 | DOI: 10.1002/adma.200690021

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