Advanced Materials

Gu, Z.‐Z.; Iyoda, T.; Fujishima, A.; Sato, O.

doi: 10.1002/1521-4095(200109)13:17<1295::AID-ADMA1295>3.0.CO;2-7pmid: N/A

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).

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

doi: 10.1002/1521-4095(200109)13:17<1298::AID-ADMA1298>3.0.CO;2-Qpmid: N/A

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.

Feldmann, C.

doi: 10.1002/1521-4095(200109)13:17<1301::AID-ADMA1301>3.0.CO;2-6pmid: N/A

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.

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

doi: 10.1002/1521-4095(200109)13:17<1303::AID-ADMA1303>3.0.CO;2-Vpmid: N/A

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.

Tolksdorf, C.; Zentel, R.

doi: 10.1002/1521-4095(200109)13:17<1307::AID-ADMA1307>3.0.CO;2-7pmid: N/A

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.

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

doi: 10.1002/1521-4095(200109)13:17<1310::AID-ADMA1310>3.0.CO;2-Apmid: N/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.

Wang, M.; Braun, H.‐G.; Kratzmüller, T.; Meyer, E.

doi: 10.1002/1521-4095(200109)13:17<1312::AID-ADMA1312>3.0.CO;2-Zpmid: N/A

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.

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

doi: 10.1002/1521-4095(200109)13:17<1317::AID-ADMA1317>3.0.CO;2-5pmid: N/A

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.

Pardo‐Yissar, V.; Gabai, R.; Shipway, A. N.; Bourenko, T.; Willner, I.

doi: 10.1002/1521-4095(200109)13:17<1320::AID-ADMA1320>3.0.CO;2-8pmid: N/A

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.

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

doi: 10.1002/1521-4095(200109)13:17<1324::AID-ADMA1324>3.0.CO;2-Lpmid: N/A

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.