Advanced Functional Materials

In-plane shrinkage in a layer covering a polymer film is used to orient the underlying polymer, in this case poly(3-hexylthiophene). By using an intermediate layer to mediate the force, alignment is achieved with minimal chemical contamination and physical damage. Crossed-polarizer microscopy, atomic force microscopy (see Figure), grazing-incidence X-ray diffraction, and polarized absorption are used to analyze the alignment.

Gold nanorods have been aligned within poly(vinyl alcohol) thin films by stretching the film, thereby allowing the polarization-dependent optical response to be studied (see Figure). Irradiation with a nanosecond laser was used to micropattern the film, by the thermal reshaping of the nanorods into nanospheres.

Gold nanorods have been aligned within poly(vinyl alcohol) thin films by stretching the film, thereby allowing the polarization-dependent optical response to be studied (see Figure). Irradiation with a nanosecond laser was used to micropattern the film, by the thermal reshaping of the nanorods into nanospheres.

Single crystals of stilbazolium derivatives with varied substituents in the para position have been grown. The crystals have high second-harmonic generation efficiency—comparable to that of 4-N,N-dimethylamino-4′-N′-methylstilbazolium tosylate. X-ray studies revealed that the p-methoxy-substituted derivative crystallizes in a triclinic space group with perfectly aligned molecular dipoles (see Figure), favorable for large nonlinear optical and electro-optical effects.

The laser-induced synthesis of carbon fibers is described. Nine distinct phases are identified, allowing a pressure–temperature phase diagram to be assembled. At ethene pressures of 3.7 bar, Raman spectra of the diamond-like fibers (see Figure) indicate an sp³ fraction of up to 89 %.

Multilayer capsules are prepared from a hydrophobically modified polyelectrolyte via layer-by-layer assembly on sacrificial substrates. The capsules possess irregular hydrophobic domains, which are infiltrated with a lipid to obtain a uniform, distinct, hydrophobic layer, imparting the capsule with a pseudobilayer vesicle structure, as shown in the Figure.

In-plane shrinkage in a layer covering a polymer film is used to orient the underlying polymer, in this case poly(3-hexylthiophene). By using an intermediate layer to mediate the force, alignment is achieved with minimal chemical contamination and physical damage. Crossed-polarizer microscopy, atomic force microscopy (see Figure), grazing-incidence X-ray diffraction, and polarized absorption are used to analyze the alignment.

A three-phase, double-percolating composite made of NiZn-ferrite and nickel particles embedded in a poly(vinylidene fluoride) matrix (see Figure) has been prepared by a simple hot-pressing method. A large enhancement in both initial permeability and dielectric constant of the three-phase composite is observed.

Polymer thin-film-transistor arrays are fabricated by stamping. The Figure shows examples of stamped polymer patterns. The polymer thin-film patterning process is caused by capillary forces that drive the polymer solution in the stamp recesses while the stamp features in contact with the substrate absorb the solvent. This stamping process is compatible with large-area roll-to-roll fabrication.

PbSe/PbS and PbSe/PbSe_xS_1–x core/shell nanocrystals (NCs), produced via two- and one-stage processes, respectively, demonstrate luminescence quantum efficiencies of 45–55 %. The core/shell NCs exhibit an energy tuning of the exciton transitions with respect to that of the core NC that is dependent on the core diameter, shell thickness, and composition (as shown in the Figure for PbSe/PbS).

The formation of large-area (>cm²), ordered monolayers of colloidal nanocrystal quantum dots (QDs) is a critical step in the fabrication of macroscale devices (such as the electroluminescent (EL) device shown in the Figure) from these unique materials. Phase separation is a robust and flexible process that enables these QD thin films to be formed in a single fabrication step.

Nanocomposite bulk electrodes of molecular hybrid materials prepared electrochemically from polyaniline (PAni) and polyoxometalates (see Figure) were prepared and tested in electrochemical supercapacitors. PAni/H₃PMo₁₂O₄₀ in particular shows strong cyclability (> 4000 cycles with small capacity loss) and a capacitance of 120 F g^–1. The hybrids require an electroactivation process to reach their optimal performance, but show much promise as energy-storage materials.

Plasma deposits have been used to uniformly coat the internal and external surfaces of a three-dimensional poly(D,L-lactic acid) scaffold with amine functionalities. This surface modification allows increased attachment of fibroblasts (see Figure) throughout the scaffold without changing the bulk characteristics of the polymer.

Can metallic silver be made acidic? Yes! By employing a novel methodology to entrap organic molecules within metals, both acidic and basic metallopolymeric composites (see Figure) are produced using silver and either the polyacid Nafion or the polybase poly(vinylbenzyltrimethylammonium hydroxide). Applications ranging from ion-exchange electrodes to bifunctional catalysts are envisaged.

A zwitter polymer is a polymer that has a linear or crosslinked structure, depending on an applied dose of electron-beam irradiation. Structural transformation of an acrylic resin makes it suitable for use as a positive and a negative resist (see Figure) in the semiconductor field. The contrast ratio and threshold dose increase with increasing resist thickness for both resists, and the positive resist exhibits better contrast than the negative.

Thermal actuators based on thin films of a liquid-crystal network with a splayed molecular order over their cross-section (see Figure) show a homogeneous bending deformation (also shown in Figure) upon heating. The origin is a difference in thermal expansion depending on the molecular orientation.

A simple route for fabricating highly ordered arrays of titania nanoparticles, via one-step spin-coating from a solution containing a titania precursor and the diblock copolymer, polystyrene-block-poly(ethylene oxide) (PS-b-PEO), is presented (see Figure). The size of the nanoparticles and the lattice spacing of the arrays can be fine-tuned by controlling the amount of sol–gel precursor relative to PS-b-PEO.

A carbon dioxide sensor based on a faujasite–Metglas composite is synthesized and characterized. The composite zeolite film on the magnetoelastic strip (see Figure) combines the property of the faujasite crystal to selectively adsorb larger amounts of CO₂ than N₂ with the property of the Metglas material to detect small mass loads. This device can be used as a remote, passive, room-temperature CO₂ sensor.

Ambipolar transport in PCBM: The methanofullerene PCBM (structure shown in Figure) is an electron acceptor and a key component of polymer solar cells. Time-of-flight mobility measurements show that PCBM dramatically increases the hole mobility of a poly(phenylene vinylene) polymer/PCBM blend, and that PCBM transports electrons and holes equally well (see Figure). This may explain the high PCBM content required for efficient solar cells.

Enhancing the metallic character of SWNTs (single-walled carbon nanotubes) is important in many applications. Using Raman spectroscopy, the authors demonstrate that the extent of anisotropic interaction between SWNTs and poly(methyl methacrylate) (PMMA) is probably responsible for variation in the electronic properties of SWNTs in composites prepared by different procedures (see Figure).

Novel poly(9,9-dioctylfluorene) copolymers containing statistically distributed binaphthyl spacer groups hinder the formation of the highly ordered β-phase in thin films of the copolymers, resulting in a dramatic reduction of the excitation density required to reach the threshold of distributed feedback lasers (see Figure). Thus, these copolymers may be useful as gain materials in organic solid-state lasers.

Structural properties of films of poly- [3-hexylthiophene-2,5-diyl]/[6,6]-phenyl C₆₁ butyric acid methyl ester (P3HT/PCBM) have been studied by X-ray diffraction. P3HT crystallites with a-axis orientation (see Figure) were observed, whereas PCBM crystallites were not found. The influence of P3HT crystallinity on the performance of P3HT/PCBM solar cells is discussed.

Anisotropic metal colloids synthesized in a homogeneous reaction environment display many different shapes, including rods, tapes, platelets, tetrahedra, and isotropic particles (see Figure). Based on this observation, a new kinetics-based mechanism explaining the formation and growth of these particles is proposed. Twin planes in metal nuclei could act as sites of enhanced kinetics for adatom attachment, creating axes of preferred crystal growth.

Color tuning of a light-emitting polymer is achieved through efficient Förster energy transfer from a higher-energy polyfluorene (PF) backbone to lower-energy pendant bis[4-(diphenylamino)styryl]fluorene (DPAS) units. An electroluminescent device based on a PF–DPAS blend in PF–triphenylamine–oxadiazole shows a voltage-independent, stable spectrum (see Figure) with a maximum external quantum efficiency of 2.08 % and a maximum brightness of 6916 cd m^–2.