Advanced Materials

Laser Ablation for polymer processing can be extended to most known classes of polymers by the addition of dopants to sensitize the polymers to UV laser radiation. The Figure shows bubble formation in polymethylmethyacrylate doped with an alkyl-diaryl-triazene with the laser fluence increasing from left to right. The dopant/polymer systems that have been investigated so far are reviewed and a general scheme containing all relevant mechanisms is suggested. fig.

Polarized electroluminescence (EL) from an oriented poly(3-alkylthiophene) structure is reported, which is a first step towards the fabrication of an organic light-emitting diode (LED) that emits polarized light. A multilayer structure is described that includes a Langmuir-Blodgett film of poly(3-decylmethoxythiophene), PDMT, in which the polyenic backbones are oriented along the dipping direction. The optical properties–absorption, EL, photoluminescence–and the I–V curve for an ITO/PDMT/Al device are presented.

The design of supramolecular templates to direct the synthesis of organized inorganic materials is illustrated for aragonite (CaCo₃), which is metastable under ambient conditions but found in gallstones, fish otoliths, etc. Spreading of the template 5-hexadecyloxyisophthalic acid at the air/water interface is shown to result in the specific nucleation of aragonitc (see Figure) from supersaturated calcium bicarbonate solution without additives.

Efficient blue electroluminescent devices based on a novel silicon-containing poly(P-phenylene) derivative are described. It is shown that the turn-on field and internal quantum efficiency can be improved by using a double-layer device configuration instead of a single-layer one and by the addition of a transport layer at the cathodic side. The combined study of electrical and optical properties on one hand and morphological aspects on the other is demonstrated to be a fruitful approach to the improved performance of organic electronics.

Highly nonlinear chromophores with good thermal stabilities (> 250 °C) are required if organic polymeric materials are to be developed for electro-optical (EO) applications. The synthesis and characterization of highly efficient and thermally stable diphenylamino-substituted thiophene stilbenes (e.g., see Figure) are reported, one of which was used to form a high-EO-coefficient composite with a polyquinoline.

A global or “systems” approach to the design of polymer-based light-emitting devices is shown to be important for an understanding of the details of light emission from these devices. A self-interference-filter type of light-emitting device with a very narrow spectral output–a prerequires for many applications but difficult to realize because of the typically broad electroluminescence emission spectrum–is described, in which color selection is achieved by the appropriate combination of layer thickness and values of refractive index of the components of the device structure.

A new class of nonlinear optical chromophores (NLO-phores) with large off-diagonal components of the second-order polarization and remarkable transparency properties have been investigated. The synthesis and NLO characterization of a series of C_2n symmetry benzene derivatives, such as that shown in the Figure, are described. The results of UV-vis, EFISH, hyper-Rayleigh scattering, etc., measurements are compared.

Hybrid molecular electrodes, based on a conducting polymer matrix containing a dispersion of an electroactive inorganic component, are reported. The phosphomolydate anion, [PMo₁₂O₄₀]^3⊖, is dispersed in polypyrrole to investigate cooperative phenomena between the components. The interactions are shown to influence the magnetic, electrical, photochemical and electrochemical properties of these composite materials.

The reliable fabrication of nanostructures is polymer materials, i.e. structures with feature sizes below 100 nm, is an important goal if progress in the application of such materials in electronic, magnetic, and optical devices is to be maintained. Replica molding has been used extensively to produce micrometer sized features. Here, the technique is extended to the nanometer regime such as that shown in the figure. fig.

The functionalization of conducting polypyrroles in high yields without the polypyrroles losing their conductivity is reported. The method is based on the use of substituted arenes as starting materials, onto which the pyrrole ring is ‘grown’. The resulting pyrrole rings have aryl groups substitued on the 3− and/or 4-positions. The aryl groups themselves can carry a wide range of substituents which can be selected in order to tune the properties of the materials. The substitued pyrolle monomers can be polymerized using standard procedures.

A new route to the formation of an electrochemically active film that contains fullerene units is reported. The method involves the reduction of C₆₀ to its dianion in the presence of dioxygen and produces a film (see Figure) that is similar, but not identical to films prepared by the electrochemical reduction of C₆₀O. This new method of fullerence polymerization therefore avoids the need for the tedious preparation and purification of C₆₀O. fig.

Pure, white, nanosized aluminum nitride powder in a wurtzite structure has been prepared using the DC are plasma method. Aluminum nitride is an important ccceramic material which exhibits high thermal conductivity, high hardness, good corrosion resistance, and low thermal expansivity. The most critical factors in the production of advanced ceramics are the purity and homogeneity of the starting powders. The new method allows the production of ultrafine, pure A1N and Al-A1N composite materials.

Opalescent films of ca. 100 cm² (see Figure and this month's cover picture) based on a renewable resource, cellulose, have been prepared. The films are based on cholesteric, semi-interpenetrating networks which result from the crosslinking of lyotropic liquid crystalline phases of cellulose carbanilates in commercial acrylates. Photocrosslinking of the films at different temperatures allowing patterning.

The process of mechanical milling of amorphous precursors can be used to produce bulk quantities of material with fine crystalline nanostructures. Here, the process and the factors which influence the quality of the materials produced are reviewed. The crystallization induced by mechanical milling and thermal annealing are compared and it is suggested that the induction of crystallization by ball milling may be a promising technique for preparing soft magnetic materials in powder form.

Molecular monolayer-based surface modification has been used extensively for three of the four important classes of electronic materials, namely metals, semiconductors, and insulators. In this article recent progress in the application of t. is technique, which is commonly called “self-assembly”, to the modification of the surfaces of high-T_c superconductors (e.g. see Figure) is reviewed.

A polymer gel is crosslinked polymer network swollen in solvent. Some gels undergo abrupt volume changes by swelling–shrinking in response to external stimuli, such as temperature or electric field. Recently a new type of biometric gel has been developed which autonomously repeats its swelling-shrinking cycles periodically in a closed solution, without any external stimuli, similar to a beating heart muscle. The new materials and their rhythmical behavior are discussed.