Advanced Materials

Synthetic composites with controlled morphologies based on calcium carbonate (see Figure) have been obtained by self-organization processes through molecular interactions between organic and inorganic substances. These hybrid materials with polymers and aligned amphiphilic molecules on the surface are a living example of how highly functionalized materials can be created by environmentally friendly techniques.

Charge-driven microencapsulation of water-soluble CdTe nanocrystals has been used to create both single-color tagged microspheres (see Figure) and multicolored beads with controlled emission intensity ratios. The concept is based on the pumping of negatively charged species into the interior of specially designed microspheres. CdTe nanocrystals brightly luminescing in the visible and near-IR were used as they are important for further use in encoding combinatorial libraries (see also cover).

The uptake of colloidal semiconductor nanocrystals by a large range of eukaryotes (see Figure) is directly correlated with the cell motility, as has been shown by comparing the motions of cancerous and healthy human breast cells. The nanocrystals are more photochemically robust than organic dyes and provide a powerful tool for studying the processes of cell motility and migration—behaviors that are responsible for metastases of primary cancers.

Cell fate can be directed by material-derived signals and an appropriate combination of signals can direct distinct cell fates. Adhesive ligands promote the multiplication of cells in direct contact with the signal, while the calcium gradient resulting from its release spatially regulates the ability of cells to differentiate (see Figure for an example of myoblasts that have formed muscle tissue).

Polymeric nanomicelles that allow control of the location of porphyrin moieties in the coronas, cores, or cores and coronas have been designed and reliably constructed by self- assembly of porphyrin-centered star polymers (see Figure). These photofunctional nanomicelles are of interest for advanced materials, pharmaceutical, and medical applications.

Porphyrin–fullerene linked systems (see Figure), which form self-assembled monolayers on ITO electrodes, exhibit enhanced photocurrent generation: This is due to a two-step electron transfer protocol—first intramolecularly from ¹P to C₆₀, then intermolecularly from the resulting C₆₀^• – to the electron carriers.

Nanomagnets have been created by the incorporation of magnetic clusters into mesoporous silica. It is shown that, for a given cluster, the pore size has a strong influence on the degree of incorporation. Furthermore, the incorporation of these nanoclusters into three-dimensional organized mesoporous silica ensures that the integrity of the host phase as well as that of the incorporated clusters is maintained. This high degree of stability opens new perspectives for the organization of nanomagnets into mesoporous silica layers or as monolayers on silica surfaces.

Films of single-walled carbon nanotubes have been obtained by simple evaporation of suspended nanotubes on a glass substrate. The technique has also been used to create patterned structures (see Figure) by treating the substrate before evaporation and thus creating hydrophobic and hydrophilic areas. The films showed orientational ordering, which could be useful for optical applications.

Layer-by-layer deposition of polythiophene (see Figure) has successfully been carried out using only polyanion and polycation dilute solutions of polythiophene. The synthesis and characterization of these assemblies, as well as their optical properties, are described. The conductivities of the regioregular polythiophenes reported are much higher than for regiorandom polythiophene multilayer systems.

Nanometer-size tin oxide particles (see Figure) with high thermal stability against particle growth have been synthesized. A low particle growth rate was achieved by doping SnO₂ particles with rare earth ions during synthesis. This technology can be applied to modify the particle surface and then control growth rate and specific electric and catalyst properties, producing nanostructured materials with improved performance.

Metallodielectric inverse opal films (see Figure) have been fabricated by templating colloidal crystals with gold–silica core–shell nanoparticles. The degree of packing order of the inverse opals was determined by the Au@SiO₂ nanoparticle diameter. The technique provides a highly versatile means of tuning the inverse opal properties through variation of the silica coating on the nanoparticle building blocks.

Highly proton-conducting glass films have been prepared by controlling the pore size of the silica film. The conductivity of films with pores perpendicular to the substrate surface is high, whereby the conductivity increases with increasing water content. The high conductivity was retained at relatively low humidity due to the restriction of water movement in the pores. These porous proton-conducting materials are of interest for use in small fuel cell systems.

Large-area polymer thin films of adjustable thickness have been prepared by a continuous bar-coating process (see Figure). The promise of this low-cost polymeric device production technology is exemplified by the fabrication of MEH-PPV-based LEDs (see inside front cover).

A “hybrid photochromic” molecule with intertwined tetraazaporphyrin and bisthienylethene (BTE) chromophores is presented. The key photo-process is the simultaneous cyclization of two BTE units (yielding the molecule shown in the Figure) with high quantum yield at RT, and with a strongly temperature-dependent yield for the reverse reaction. The molecule is, thus, an ideal candidate for non- destructive readout optical memory devices.

High-speed persistent spectral hole burning (PSHB), 30 times faster than in a similar H₂ gas treated glass, has been achieved for a samarium(II)-doped alumina–silica glass upon irradiation with X-rays. Glasses of this type, enabling fast and highly efficient hole burning, are excellent candidates for binary high-density memory devices. Hole burning probably proceeds by a novel mechanism, i.e., the reaction of the X-ray irradiation-generated Sm²⁺ ions with oxygen ions to re-establish the original, stable trivalent oxidation state of samarium.

Zeolitic wood structures made by a seeded templating process offer new ways of investigating the complex wood morphology. The technique can also be used to create hierarchical porous zeolitic materials (see Figure). The seeded growth strategy shows potential for the extension to any organisms with hierarchical structure and might make multilevel porous zeolites of other types feasible.

Ordered arrays of metallic domes, dots, and pores can be produced by exploiting a combination of colloidal templating and “over sputtering”. This elegant method involves deposition of metal onto a layer of polystyrene latex beads. The beads are then removed by heating to leave dome-shaped metal “shells” (see Figure). Upon further heating the domes can be converted to metallic dots. Pores are obtained if colloidal multilayers are used.