Advanced Materials

Polymeric thin films have been prepared by solventless processes that are particularly suitable for building block copolymers into multilayer films (see Figure for an optical image of a two-layer film, scale bar = 50 μm). Using this method, the detrimental effects that a solvent may sometimes have when preparing a film can be avoided.

Wrapped polymer chains, consisting of a single strand of a positively charged polymer as stuffing and a thin silicate skin, have been obtained by mixing a polymeric viologen bromide and sodium silicate in basic medium. The nanostrands, which are 2.5 nm wide and up to 60 nm long, were visualized by transmission electron microscopy with Gd³⁺ staining (see Figure, scale bar = 10 nm).

Regular arrays of microstructures arise from capillary interactions when a patterned elastomeric mold is placed on top of a line-and-space patterned polymer at an angle and the polymer is heated above its glass transition temperature. The Figure shows a self-organized microstructure obtained from 90°-shifted molds with line-and-space patterns by annealing at 130 °C for 60 min.

Self-organized anisotropic ion-conductive materials can be formed by the interactions between a conventional ionic liquid and hydroxyl-terminated mesogenic compounds. Anisotropic ionic conductivities could be measured for samples that formed oriented monodomains in the measurement cell. The Figure shows the ionic liquid and mesogenic compound in the cells used for these measurements. (See also cover)

A dye-sensitized photoelectrochemical cell (see Figure) is described and its construction and performance reported: the overall efficiency of the cell is the highest recorded so far for solid-state cells. The major novelty of the cell lies in its gel electrolyte made by the sol–gel route.

Tridirectional conductivity in a polymeric material has been achieved. Nanoscale “wires” formed via hierarchical self-organization of a basic block copolymer and a monomeric acid/alkylphenol complex establish a lamellar-within-lamellar superstructure (see Figure), resulting in a soft material with tunable conductivity and anisotropy.

What enhances the energy transfer between oppositely charged polyelectrolytes in water? To evaluate this, the authors synthesized oligo- and polymeric counterions (see Figure for an example of a polycation) and measured fluorescence quenching. The effect was biggest for polymers in the presence of a large excess of surfactant, stressing the influence of supramolecular aggregation of the chromophores.

Nanobamboos have been created by chemical vapor deposition of boron nitride (BN). Strands of nanobamboos (see Figure), nanotubes, or nanocables are formed depending on the oxygen content of the precursor material. An insufficent supply of boron oxide leads to capped (bell) structures, which form in order to minimize the surface energy of the tubular layers.

Conducting polymers that contain host–guest complex units have been synthesized by electropolymerization of bis-(bithiophene)-substituted tungsten-capped calixarenes (see Figure for general formula). The guest molecule, weakly bonded to the tungsten atom, participates in electron transport. Hence, the conductivity depends on the guest’s chemical nature, making the polymer potentially useful as a small-molecule sensor.

n-Type field-effect transistors (see Figure) with electron mobilities as high as 5 × 10^–4 cm²/V s —the highest field-effect mobility of electrons observed to date in a conjugated polymer—have been obtained. Improvements in the purification and control of the morphology of thin films should result in even higher electron mobilities for this type of conjugated polymers.

Keto defect sites play a key role as the source of low-energy emission bands in polyfluorene type materials. The formation of fluorenone defect sites can be regarded as a dominant degradation mechanism in light-emitting devices based on polyfluorenes. The superiority of difunctionalization (see Figure) at the methylene group in –CR₂– bridged polyphenylene and polyarylene derivatives is illustrated.

Ordered nanoporous materials with uniform pore shape and wall structure have been prepared from selected diblock copolymers. Fine-tuning of the pore size and wall thickness is possible by controlling the micelle size (see Figure). The formation mechanism of these nanoporous structures is confirmed by both liquid- and solid-state ¹³C and ²⁹Si NMR techniques.

Aligned MWNT–PPy composite films show exceptional charge storage capacities and improved response times. The superior performance of these composites, compared to pure PPy films, is demonstrated and discussed. The Figure shows an SEM image of the fractured film cross section, illustrating the thickness of the PPy coating as well as the channels available to the electrolyte.

Unique molecular-recognition microcapsules for environmental stimuli-responsive controlled release have been developed. The microcapsules consist of a core–shell porous membrane. The pores contain linear-grafted poly(NIPAM-co-BCAm) chains, which act as the molecular-recognition gates. The Figure shows the mechanism of the opening of the pores to release the molecules inside.