Advanced Materials

Cover image for Vol. 13 Issue 17

September, 2001

Volume 13, Issue 17

Pages 1295–1342

    1. Photo-Reversible Regulation of Optical Stop Bands (pages 1295–1298)

      Z.-Z. Gu, T. Iyoda, A. Fujishima and O. Sato

      Version of Record online: 30 AUG 2001 | DOI: 10.1002/1521-4095(200109)13:17<1295::AID-ADMA1295>3.0.CO;2-7

      Photo-reversible tunable photonic crystals have been fabricated by the infiltration of photochromic dyes into the voids of opal films. The enhanced changes in refractive indices due to the resonance effect of the dyes regulate the stop bands of the dyed opals. All changes can be reversibly tuned back and forth (see Figure) giving these photonic crystals excellent potential for applications in optical transfer devices (see also cover).

    2. Photoimaging on an Optically Anisotropic Film with a Polymerizable Smectic Liquid Crystal (pages 1298–1301)

      J. Y. Chang, S. W. Nam, C. G. Hong, J.-H. Im, J.-H. Kim and M. J. Han

      Version of Record online: 30 AUG 2001 | DOI: 10.1002/1521-4095(200109)13:17<1298::AID-ADMA1298>3.0.CO;2-Q

      The orientation under an electric field of a smectic A phase liquid crystal (LC) is unveiled in this communication. The authors have prepared a rod-like LC consisting of two photoreactive chalcone units and have carried out photopolymerization by UV irradiation. The Figure shows the image patterns observed under a polarizing microscope. Applications of this technique may include microscopic patterning.

    3. Preparation of Nanoscale Pigment Particles (pages 1301–1303)

      C. Feldmann

      Version of Record online: 30 AUG 2001 | DOI: 10.1002/1521-4095(200109)13:17<1301::AID-ADMA1301>3.0.CO;2-6

      Pigment particles on the nanoscale, required for applications such as transparent thin films, inks, and coatings, can be prepared by the polyol process. The fabrication of nanoscale particles of major commercial pigments, e.g., CoAl2O4 (blue), Cr2O3 (dark green), and α-Fe2O3 (red) (see Figure), is complicated by the fact that their body color is strongly related to their degree of crystallinity. The polyol method yields crystalline and colloidally stable pigments.

    4. Efficient Continuous-Wave Two-Photon Absorption in para-Phenylene-Type Polymers (pages 1303–1307)

      A. Hohenau, C. Cagran, G. Kranzelbinder, U. Scherf and G. Leising

      Version of Record online: 30 AUG 2001 | DOI: 10.1002/1521-4095(200109)13:17<1303::AID-ADMA1303>3.0.CO;2-V

      Two-photon materials—in particular those with well-defined two-photon absorption (2PA) with a high 2PA cross section—have potential applications in three-dimensional data storage, for example. The 2PA cross section of ladder-type poly(p-phenylene) is found here to be one of the highest reported for organic materials. Concentration- and temperature-dependent measurements show that the absorption is a purely intra-chain process and that the effective conjugation length has an important impact on the 2PA cross section—in accordance with theory.

    5. Reversible Physical Network Stabilized Ferroelectric Liquid Crystals (pages 1307–1310)

      C. Tolksdorf and R. Zentel

      Version of Record online: 30 AUG 2001 | DOI: 10.1002/1521-4095(200109)13:17<1307::AID-ADMA1307>3.0.CO;2-7

      A new route to thermoreversible networks through gelling ferroelectric liquid crystals is presented. A reversible stabilization of one polar state can be achieved. On heating the gel, the network and therewith the polar orientation will be destroyed and on cooling a new polar orientation can be rebuilt. The Figure shows a schematic representation of the gel network formed by self-assembly.

    6. Synthesis of Macrostructured Silica by Sedimentation–Aggregation (pages 1310–1312)

      S. Vaudreuil, M. Bousmina, S. Kaliaguine and L. Bonneviot

      Version of Record online: 30 AUG 2001 | DOI: 10.1002/1521-4095(200109)13:17<1310::AID-ADMA1310>3.0.CO;2-A

      Highly stable silicas characterized by narrow pore size distribution in the macroscale range have been synthesized using a novel and simple route based on sedimentation–aggregation of monodisperse polystyrene (PS) beads. The network of macropores and macrowindows is preserved upon calcination up to 900 °C. The Figure shows an SEM image of PS beads after sedimentation, vacuum drying, and dispersion in acetone.

    7. Patterning Polymers by Micro-Fluid-Contact Printing (pages 1312–1317)

      M. Wang, H.-G. Braun, T. Kratzmüller and E. Meyer

      Version of Record online: 30 AUG 2001 | DOI: 10.1002/1521-4095(200109)13:17<1312::AID-ADMA1312>3.0.CO;2-Z

      Equally sized and regularly spaced polymer dots can be produced by the new approach, based on microcontact printing, described here. It is shown that the printed dots are smaller than the protrusions of the stamp used and result from the transfer of polymer dot-like aggregates formed by a topographically controlled dewetting process (see Figure) of the polymer solution on the microstructured stamp surface.

    8. Structure Determination of Spherical MCM-41 Particles (pages 1317–1320)

      B. Pauwels, G. Van Tendeloo, C. Thoelen, W. Van Rhijn and P. A. Jacobs

      Version of Record online: 30 AUG 2001 | DOI: 10.1002/1521-4095(200109)13:17<1317::AID-ADMA1317>3.0.CO;2-5

      Experimental observations from (sub-)micrometer spheres of silica are compared with the results from conventional MCM-41 material. SEM images give proof of a spherical morphology (see Figure), which is also confirmed by TEM. XRD patterns confirm that on a local scale the pores are hexagonally packed whilst on a larger scale, the pore ordering is disturbed.

    9. Gold Nanoparticle/Hydrogel Composites with Solvent-Switchable Electronic Properties (pages 1320–1323)

      V. Pardo-Yissar, R. Gabai, A. N. Shipway, T. Bourenko and I. Willner

      Version of Record online: 30 AUG 2001 | DOI: 10.1002/1521-4095(200109)13:17<1320::AID-ADMA1320>3.0.CO;2-8

      A new approach to the construction of functional materials is demonstrated. Gold nanoparticles immobilized in a polymer hydrogel allow external control over the conductivity by switching the gel between its swollen and shrunken states. This reversible cycling (see Figure) controls the interparticle distances between the Au nanoparticles, which may lead to new methods in sensing and catalysis.

    10. Smart Micro- and Nanocontainers for Storage, Transport, and Release (pages 1324–1327)

      G. Ibarz, L. Dähne, E. Donath and H. Möhwald

      Version of Record online: 30 AUG 2001 | DOI: 10.1002/1521-4095(200109)13:17<1324::AID-ADMA1324>3.0.CO;2-L

      A defined and controllable permeability of the capsule wall of hollow polyelectrolyte capsules has been achieved. The walls of these capsules can be switched between an open and a closed state with respect to macromolecules by adjusting the salt concentration of the solution in which the capsules are dispersed. The Figure shows part of the mechanism to encapsulate and release macromolecules by this method.

    11. Sol–Gel-Coated Quartz Crystal Microbalances for Monitoring Automotive Oil Degradation (pages 1327–1330)

      F. L. Dickert, W. Greibl, A. Rohrer and G. Voigt

      Version of Record online: 30 AUG 2001 | DOI: 10.1002/1521-4095(200109)13:17<1327::AID-ADMA1327>3.0.CO;2-3

      Detecting the degradation of automotive engine oils is an environmentally important task. The combination of a molecularly imprinted ceramic layer with a mass-sensitive device (e.g., a quartz crystal microbalance, QCM) is shown to provide a cheap and easy-to-use method of continuously checking the aging of oil in a car engine. In the approach presented, carboxylic acids formed by oxidation processes are extracted by hydrogen bonding to basic interaction sites on sol–gel layers on a QCM, which leads to a frequency response of the QCM.

    12. Catalytic Growth of Semiconducting In2O3 Nanofibers (pages 1330–1333)

      C. H. Liang, G. W. Meng, Y. Lei, F. Phillipp and L. D. Zhang

      Version of Record online: 30 AUG 2001 | DOI: 10.1002/1521-4095(200109)13:17<1330::AID-ADMA1330>3.0.CO;2-6

      In2O3 nanofibers have been prepared by using a thermal evaporation–oxidation method. The nanofibers generally show rectangular cross sections (see Figure) with different width-to-thickness ratios. The photoluminescence spectrum of these nanowires shows light emission in the blue-green region. By doping with other elements potential applications in opto-electronic nanodevices and nanosized gas sensors could be achieved.

    13. Sub-Nanometer Noble-Metal Particle Host Synthesis in Porous Silica Monoliths (pages 1333–1336)

      L. M. Bronstein, S. Polarz, B. Smarsly and M. Antonietti

      Version of Record online: 30 AUG 2001 | DOI: 10.1002/1521-4095(200109)13:17<1333::AID-ADMA1333>3.0.CO;2-P

      Sub-nanometer noble-metal particles regularly located along the pore walls of freshly prepared silica monoliths have been synthesized. A very effective method of size restriction, presumably via a template mechanism of the entries of the micropore system, is shown to exist. Ordered mesoporous oxide can thus be a perfect host for inclusion of metal particles in 3D structures. The formation and stabilization of such tiny particles in highly porous material opens exciting prospects for catalytic applications.

    14. A Photoinduced Birefringent Film with a High Orientational Order Obtained from a Novel Polymer Liquid Crystal (pages 1337–1339)

      N. Kawatsuki, T. Kawakami and T. Yamamoto

      Version of Record online: 30 AUG 2001 | DOI: 10.1002/1521-4095(200109)13:17<1337::AID-ADMA1337>3.0.CO;2-1

      A novel photo-crosslinkable polymer liquid crystal (PCP-LC), in which a high molecular orientation has been achieved by irradiation with UV light and thermal treatment, is presented. Two types of optical birefringent film have been obtained whereby the orientational order is controlled by the irradiation angle and polarization of the UV light. The Figure shows the viewing angle dependence of the two films between crossed polarizers.

    15. Layer-by-Layer Self-Assembly of Polyelectrolyte and Low Molecular Weight Species into Capsules (pages 1339–1342)

      Z. Dai, A. Voigt, S. Leporatti, E. Donath, L. Dähne and H. Möhwald

      Version of Record online: 30 AUG 2001 | DOI: 10.1002/1521-4095(200109)13:17<1339::AID-ADMA1339>3.0.CO;2-Q

      Composite capsules containing low molecular weight species together with charged macromolecules have been prepared both in aqueous and organic solutions. Dyes were used as building blocks to quantify the adsorption. The Figure shows a tapping mode scanning force microscopy image of capsules consisting of poly(styrene sulfonate) and benzoquinone layers templated on melamine formaldehyde particles (see also inside front cover).