Advanced Functional Materials

Biomineralized polysaccharide capsules (see Figure, center, and cover) provide microenvironments for encapsulation of human cells (top left) and biomolecules that lead to tissue formation. Embedded “host” capsules (bottom left) enable spatial separation of cell populations and temporal release of biological factors. Bone matrix formation is demonstrated (bottom right).

The influence of pulse height and pulse duration on the local oxidation of self-assembled monolayers of octadecyl trichlorosilane using scanning probe nanolithography is studied (see inside cover). A narrow window is found in which the terminal methyl groups of the monolayer are converted to carboxylic acid groups, as shown in the Figure.

Introducing dove-tailed alkyl chains onto the aromatic core of hexa-peri-hexabenzocoronene derivatives dramatically lowers the isotropization temperature (T_i), allowing thermal processing from the isotropic phase at practical temperatures. The effect of alkyl-chain length on T_i is investigated, as is the importance of a heteroatom in the side chain on the homeotropic self-assembly of the compounds between two surfaces (see Figure) and on a single surface.

Chemical incorporation of viologen into poly{1,4-bis[2-(3,4-ethylenedioxy)thienyl]benzene} provides plentiful multicolor electrochromism ranging from highly transparent light blue to four other colors, since both the pendant and the backbone have cathodic coloring characteristics and their redox-potential ranges do not overlap.

Well-dispersed multiwalled carbon nanotube (MWNT)/ polystyrene nanocomposites (see Figure) are prepared via melt extrusion, using trialkylimidazolium tetrafluoroborate (DMHDIm-TFB)-compatibilized MWNTs. Quantification of the nanodispersion was realized via transmission electron microscopy (TEM) and laser scanning confocal microscopy image analysis. The Figure shows a TEM image of polystyrene with 1:1 imidazolium-treated MWNT and the corresponding analysis plot.

Biomineralized polysaccharide capsules (see Figure, center, and cover) provide microenvironments for encapsulation of human cells (top left) and biomolecules that lead to tissue formation. Embedded “host” capsules (bottom left) enable spatial separation of cell populations and temporal release of biological factors. Bone matrix formation is demonstrated (bottom right).

The optical constants of five poly- fluorenes have been deduced using spectroscopic ellipsometry (see Figure) and employed to characterize the waveguiding conditions that hold for thin-film asymmetric slab structures, including cut-off thicknesses (40–70 nm) and confinement factors (between 37 % and 63 %).

Real-time X-ray microradiography is used to explore the localized electrochemical deposition of a copper structure. The authors show the importance of the distance between the electrode and the growing structure in determining the morphology of the final product and its lateral resolution. Using a two-step procedure, a high-aspect-ratio structure with good lateral resolution has been fabricated (see Figure).

The influence of pulse height and pulse duration on the local oxidation of self-assembled monolayers of octadecyl trichlorosilane using scanning probe nanolithography is studied (see inside cover). A narrow window is found in which the terminal methyl groups of the monolayer are converted to carboxylic acid groups, as shown in the Figure.

Ultrathin, flexible composite membranes are constructed via the layered assembly of ionically conductive multilayer thin films on a porous polycarbonate membrane. Under ambient conditions, a fuel cell using a poly(ethylene oxide)/poly(acrylic acid) membrane (see Figure) delivers a maximum power density of 16.5 mW cm^–2 at a relative humidity of 55 %, close to that of some commercial fuel cells.

Manganese-containing mesoporous silica has been prepared by the in-situ reduction of KMnO₄ by a surfactant template in the pores of the mesoporous material. These materials exhibit a high catalytic activity for CO oxidation: complete conversion can be achieved at around 300 °C. Furthermore, the catalyst is stable and can be used repeatedly (see Figure).

Monodisperse Au@SiO₂nanoparticles (see Figure) are prepared via a facile synthesis. After functionalization and bioconjugation, the particles are used for the fast, colorimetric detection of DNA and protein, based on the sequence-specific hybridization properties of DNA and the specific binding affinity between proteins, respectively.

xZnO·Rh₂O₃ (x = 0.5–2.0) comprise the only p-type amorphous oxide semiconductors found to date. Their atomic structures, electronic structures, and carrier-transport properties are examined in relation to their chemical composition. All the films exhibit carrier-transport properties similar to those of crystalline ZnRh₂O₄. The electronic structure of an amorphous oxide p/n junction is also discussed.

Functionalized-carbon-nanotube-based poly(vinyl alcohol) composites have been prepared through simple mixing. The nanotubes and the matrix strongly interact, and significant mechanical improvement is obtained on the addition of even small amounts of functionalized nanotubes to the polymer (see Figure for tensile modulus), which reflects the efficient matrix-to-tube load transfer.

A novel class of polyfluorenes are functionalized so as to increase the biphenyl twist angle. The optical and electroluminescence properties of these materials demonstrate suppression of the well-known green emission band. The Figure demonstrates the progression of the photoluminescence spectra of a copolymer of a non-substituted polyfluorene and an oxepin-functionalized polyfluorene (PF6-O) for increasing proportions of the oxepin moiety.

A nanoporous gold electrode has been fabricated via electrochemical alloying/dealloying of Au–Zn in a ZnCl₂-based ionic liquid (see Figure). This electrode is functionalized by the self-assembly of L-cysteine monolayers on its surface, showing excellent performance for detecting Cu(II) ions in aqueous solution.

Bifunctional devices based on polymer-dispersed liquid crystals, which host electrochromic guest molecules, have been prepared (see Figure) and investigated. Such devices allow both an independent and fast switching from a scattering opaque state to a transmissive transparent state, and a color change from white (or pale yellow) to dark blue.

A new family of layered perovskites, with the formula La₄Sr_n–4Ti_nO_3n+2, has been investigated in order to understand the mechanism of incorporating excess oxygen into perovskite lattices. The structure evolves from well-defined layered phases (see Figure a) to cubic phases (see Figure b), where the excess oxygen is accommodated within the perovskite framework in randomly distributed short-range linear defects.

Fe-doped synthetic chrysotile nanotubes have been prepared, with morphologies readily controlled by the amount of Fe present. Increasing Fe content leads to decreased crystallinity and a flatter structure. Chrysotile nanocrystals usually form “cylinder-in-cylinder” arrangements (see Figure), and, interestingly, repeatedly form flat aggregates consisting of four individual tubes when containing higher than 0.57 wt.-% Fe.

Solution-based anodization of titanium offers the possibility of exceptionally cheap manufacture of high-quality, ultra-thin TiO₂ films on plastic substrates. In conjunction with organic semiconductors, such thin films can be employed to produce transistors operating well below 1 V. The simplicity of the process (see Figure) makes the commercialization and integration of these devices in inexpensive, disposable, flexible, and mobile products possible.

Using the first organic spin ladder, a dithiophene-tetrathiafulvalene salt ((DT-TTF)₂[Au(mnt)₂] (mnt = maleonitriledithiolate)), as a model compound, two approaches to obtain new spin-ladder magnetic systems are described. Modification of the acceptor complex produces new organic spin ladders (structure and electron paramagnetic resonance spin susceptibility shown in Figure).

A new method for synthesizing water-stable, magnetic multishell colloids has been designed. It combines the well-known advantages of the layer-by-layer self-assembly of polyelectrolytes and the adsorption of in-situ-produced metallic clusters, offering interesting possibilities for the design of composite core–shell particles (see Figure).

The optical-amplification potential of an erbium complex, formed in-situ in a gel, is discussed. The properties of the erbium-doped gel are investigated, and compared to those of the pure complex. Experimental data (from infrared, diffuse reflectance, and fluorescence spectroscopy) and a theoretical, Judd–Ofelt analysis (see Figure) are used to highlight the potential this new gel has for telecommunications applications.