Advanced Materials

Cover image for Advanced Materials

August, 1999

Volume 11, Issue 12

Pages 975–1051

    1. Zeolite Membranes (pages 975–996)

      Adalgisa Tavolaro and Enrico Drioli

      Article first published online: 18 AUG 1999 | DOI: 10.1002/(SICI)1521-4095(199908)11:12<975::AID-ADMA975>3.0.CO;2-0

      Zeolite membranes are the focus of much active research due to their extensive potential applications, particularly their superior catalytic and separation properties. Synthesis methods and properties are presented here and compared with those of the zeolite crystalline powders. This review concentrates on composite membranes, the Figure showing the surface of an alumina composite membrane with MOR structure.

    2. Two-Dimensional Sol-Gel Synthesis of Hetero-Layered Nanostructure Composed of Ultrathin TiO2 and ZrO2 Laminae (pages 997–1000)

      Isamu Moriguchi, Yoshihiro Tsujigo, Yasutake Teraoka and Shuichi Kagawa

      Article first published online: 18 AUG 1999 | DOI: 10.1002/(SICI)1521-4095(199908)11:12<997::AID-ADMA997>3.0.CO;2-L

      Ultrathin films of alternating oxide layers have been prepared using a 2D sol-gel process. The individual layers of TiO2 (lighter) and ZrO2 (darker) can be seen in the high-resolution TEM image shown in the Figure. The 2D sol-gel process allows the thickness of the individual layers—and of the total structure—to be simply and accurately controlled at a sub-nanometer level.

    3. Effects of Film Crystallinity on the Protective Properties of Self-Assembled Monolayers of Alkanethiols on Copper (pages 1000–1003)

      G. Kane Jennings, Jeffrey C. Munro and Paul E. Laibinis

      Article first published online: 18 AUG 1999 | DOI: 10.1002/(SICI)1521-4095(199908)11:12<1000::AID-ADMA1000>3.0.CO;2-1

      Packing and structure within ultrathin organic films can have a dramatic impact on bulk and interfacial properties, such as the ability of the film to provide corrosion resistance to the underlying substrates, especially to microelectronic devices. This communication provides a molecular- level examination of the effect of crystallinity on the protection provided to copper by crystalline self-assembled monolayers of n-alkanethiols. These ultrathin films, formed by a simple chemisorption process, are shown to be even more protective than thicker polymer films.

    4. A Chemical Synthesis of Periodic Macroporous NiO and Metallic Ni (pages 1003–1006)

      Hongwei Yan, Christopher F. Blanford, Brian T. Holland, Michael Parent, William H. Smyrl and Andreas Stein

      Article first published online: 18 AUG 1999 | DOI: 10.1002/(SICI)1521-4095(199908)11:12<1003::AID-ADMA1003>3.0.CO;2-K

      A new and general way to prepare porous metals with highly ordered 3D arrays of void spaces is reported here. The technique involves filling the spaces between colloidal crystals in a 3D array with a metal ion solution, and removing the solvent to produce a salt skeleton. The skeleton then undergoes chemical transformation to produce a metallic framework, such as that of Ni (shown in the Figure), with pore sizes of a few hundred nanometers.

    5. Layer-By-Layer Assembly of Core-Shell Magnetite Nanoparticles: Effect of Silica Coating on Interparticle Interactions and Magnetic Properties (pages 1006–1010)

      Farkhad G. Aliev, Miguel A. Correa-Duarte, Arif Mamedov, John W. Ostrander, Michael Giersig, Lius M. Liz-Marzán and Nicholas A. Kotov

      Article first published online: 18 AUG 1999 | DOI: 10.1002/(SICI)1521-4095(199908)11:12<1006::AID-ADMA1006>3.0.CO;2-2

      Layered magnetic materials have been prepared using layer-by-layer deposition, a technique that allows engineering of the structure of individual particles while remaining simple to carry out. Organic–inorganic sandwich films of superparamagnetic Fe3O4 thus prepared consisted of densely packed assemblies of Fe3O4 nanocrystallites that showed good adhesion to a variety of substrates and excellent mechanical properties. Coating the nanoparticles with a shell of SiO2 was found to greatly reduce the cooperative magnetization switching between adjacent nanoparticles.

    6. Room Temperature Sonoelectrochemical Synthesis of Molybdenum Sulfide Fullerene-Like Nanoparticles (pages 1010–1013)

      Yitzhak Mastai, Moshe Homyonfer, Aharon Gedanken and Gary Hodes

      Article first published online: 18 AUG 1999 | DOI: 10.1002/(SICI)1521-4095(199908)11:12<1010::AID-ADMA1010>3.0.CO;2-#

      Electrochemistry and sonochemistry have been combined to prepare fullerene-like structures of MoS2 at room temperature and in high yield. Either electrodeposition or ultrasonic irradiation alone results in amorphous products, whereas the application of an electric current pulse followed by a burst of ultrasonic energy gives rise to well-crystallized MoS2 structures such as the polyhedron shown in the Figure.

    7. Organized Functionalization of Mesoporous Silica Supports Using Prefabricated Metal–Polymer Modules (pages 1014–1018)

      Nicola T. Whilton, Beate Berton, Lyudmila Bronstein, Hans-Peter Hentze and Markus Antonietti

      Article first published online: 18 AUG 1999 | DOI: 10.1002/(SICI)1521-4095(199908)11:12<1014::AID-ADMA1014>3.0.CO;2-C

      Porous silica frameworks containing well-dispersed metal particles are particularly important in catalysis. These authors report a method for direct inclusion of metal nanoparticles into a host framework, thus circumventing the need for post-synthesis functionalization of the support. The method involves a new molecular hybrid templating technique that exploits the ability of the functionalized polymer microgel to function as both an exotemplate (controlling the growth of the metal colloids) and as an endotemplate (during the casting of the mesoporous sol-gel silicas), thus allowing the 3D arrangement of metal particles to be controlled.

    8. Self-Assembly of Rod–Coil Molecules in a Polymerizable Solution (pages 1018–1021)

      Myongsoo Lee, Deuck-Woo Jang, Yoon-Sok Kang and Wang-Cheol Zin

      Article first published online: 18 AUG 1999 | DOI: 10.1002/(SICI)1521-4095(199908)11:12<1018::AID-ADMA1018>3.0.CO;2-P

      Control over supramolecular architecture is a driving force for the design of structurally novel self-assembling materials such as the rod–coil molecules described here. Composed of a hydrophobic “rod“ and a hydrophilic “coil“, the molecules display mesomorphic phase behavior (a hexagonal columnar mesophase is depicted in the Figure) that can be controlled by selective solvation.

    9. Orthogonal Self-Assembly on Colloidal Gold-Platinum Nanorods (pages 1021–1025)

      Benjamin R. Martin, Daniel J. Dermody, Brian D. Reiss, Mingming Fang, L. Andrew Lyon, Michael J. Natan and Thomas E. Mallouk

      Article first published online: 18 AUG 1999 | DOI: 10.1002/(SICI)1521-4095(199908)11:12<1021::AID-ADMA1021>3.0.CO;2-S

      The preparation of micrometer to nanometer-sized building blocks that can be selectively derivatized is reported here. Segmented multi-metal rods of controllable length (see Cover) were fabricated by electroplating in porous template membranes. Additionally it is shown how the surface chemistry of different parts within a single particle can be controlled by means of orthogonal self-assembly. Exploiting of the different reactivities of Pt and Au towards thiols and isocyanides leads to the observation of fluorescence from only the Au segments of the rods.

    10. Photosensitive Cholesteric Copolymers with Spiropyran-Containing Side Groups: Novel Materials for Optical Data Recording (pages 1025–1028)

      Alex Y. Bobrovsky, Natalia I. Boiko and Valery P. Shibaev

      Article first published online: 18 AUG 1999 | DOI: 10.1002/(SICI)1521-4095(199908)11:12<1025::AID-ADMA1025>3.0.CO;2-4

      The thermal and chemical reversibility of the photochromic process displayed by spiropyran (see Figure) is combined with the helical supramolecular architecture of a cholesteric polymer to produce a copolymer that can be used for reversible data recording on colored backgrounds. The cholesteric structure is able to reflect a broad spectrum of visible light, which should allow the realization of the special filters and reflectors required for complex multicolor optical display devices.

    11. Efficient Polymerization of Aniline at Carbon Nanotube Electrodes (pages 1028–1031)

      Christine Downs, John Nugent, Pulickel M. Ajayan, David J. Duquette and Kalathur S. V. Santhanam

      Article first published online: 18 AUG 1999 | DOI: 10.1002/(SICI)1521-4095(199908)11:12<1028::AID-ADMA1028>3.0.CO;2-N

      High surface area conducting polymers with nanoscale dimensions are an important aim for device applications. Here is reported the polymerization and electrochemical oxidation of aniline at multiwalled carbon nanotube electrodes. Polyaniline films formed on these nanotube whiskers are oxidized more easily and produce a higher current density during the anodic oxidation compared to conventional electrodes such as those made from Pt. Scanning electron microscopy images indicate that the morphology of the films is granular, consisting of nanosized domains.

    12. Creating Microstructures of Luminescent Organic Thin Films Using Layer-by-Layer Assembly (pages 1031–1035)

      Sarah L. Clark, Erik S. Handy, Michael F. Rubner and Paula T. Hammond

      Article first published online: 18 AUG 1999 | DOI: 10.1002/(SICI)1521-4095(199908)11:12<1031::AID-ADMA1031>3.0.CO;2-Q

      Ultrathin film devices is one of the aims for the layer-by-layer assembly of charged species. These authors have used microcontact printing of self-assembled monolayers to pattern a ruthenium-based luminescent dye system on a surface (see the optical micrograph shown in the Figure). Hydrogen bonding and hydrophobic interactions are revealed to be critical to the selectivity of this process.

    13. The Joining of Parallel Plates via Organic Monolayers: Chemical Reactions in a Spatially Confined System (pages 1035–1038)

      Gertrud Kräuter, Yvonne Bluhm, Christoph Batz-Sohn and Ulrich Gösele

      Article first published online: 18 AUG 1999 | DOI: 10.1002/(SICI)1521-4095(199908)11:12<1035::AID-ADMA1035>3.0.CO;2-2

      Chemical reactions at monolayers are usually carried out by exposing the solid surface to reactive species in the liquid or gas phase. Here is investigated interactions including chemical reactions between two monolayers that are immobilized on two opposing solid substrates, a phenomenon known as wafer bonding. Covalent S–S bonds were formed in a photochemical reaction between disulfide groups on organosilane solid films under mild conditions, and the resulting bonded wafer pairs were found to have better fracture surface energy than the thermally bonded wafer

    14. Formation of Patterned Microstructures of Conducting Polymers by Soft Lithography, and Applications in Microelectronic Device Fabrication (pages 1038–1041)

      Weng Sing Beh, In Tae Kim, Dong Qin, Younan Xia and George M. Whitesides

      Article first published online: 18 AUG 1999 | DOI: 10.1002/(SICI)1521-4095(199908)11:12<1038::AID-ADMA1038>3.0.CO;2-L

      Micromolding in capillaries (MIMIC)has been used to form patterned relief structures with lateral dimensions as small as ∼350 nm. The microstructure in the figure consists of polyaniline (on an insulating Si/SiO2 base) that has been converted into the emeraldine salt to yield a conductive microstructure that could subsequently be used as a patterned electrode in fabricating all-plastic field effect transistors.

    15. Inverse CVD: A Novel Synthetic Approach to Metallized Polymeric Films (pages 1043–1047)

      Robin E. Southward and David W. Thompson

      Article first published online: 18 AUG 1999 | DOI: 10.1002/(SICI)1521-4095(199908)11:12<1043::AID-ADMA1043>3.0.CO;2-C

      Highly reflective and conductive silver surfaces on flexible polyimide films have been achieved by a novel single-stage self-metallizing procedure that utilizes similar chemistry to that involved in CVD. The film is cast as a silver(I)-doped poly(amic acid) solution. Thermal curing leads to cycloimidization of the polyimide precursor with concomitant silver(I) reduction. The result is a reflective and conductive surface approaching that of the native metal, while the film retains the essential mechanical and thermal characteristics of the parent film.

    16. Cellulose Films as Alignment Layers for Liquid Crystals: Application of Flow-Induced Molecular Orientation (pages 1049–1051)

      Noriyasu Mori, Masateru Morimoto and Kiyoji Nakamura

      Article first published online: 18 AUG 1999 | DOI: 10.1002/(SICI)1521-4095(199908)11:12<1049::AID-ADMA1049>3.0.CO;2-D

      An important feature of liquid crystal displays is surface alignment of the LCs. While mechanical rubbing has been used extensively to induce such alignment, this process also produces dust and static electricity. However, surface alignment in films of hydroxypropylcellulose has recently been achieved in situ during high-speed thin film production, which utilizes the long relaxation time of flow-induced orientation (see Figure). Results are summarized in this report.