Showing papers in "Advanced Materials in 1995"

New polymer electrolyte nanocomposites: Melt intercalation of poly(ethylene oxide) in mica‐type silicates

Abstract: Polymer electrolyte nanocomposites have been synthesized by direct melt intercalation of poly(ethylene oxide) (PEO) in layered silicates. Intercalation of the polymer chains in the silicate galleries greatly suppresses their tendency to crystallize. The conductivity of PEO/Li + -montmorillonite nanocomposite containing 40 wt% PEO is 1.6x10 -6 S/cm at 30°C and exhibits a weak temperature dependence with an activation energy of 2.8 kcal/mol

Precursor‐derived Covalent Ceramics*

Abstract: The purpose of this paper is to review some recent developments inthe field of the synthseis of covalent ceramics such as carbides and nitrides by pyrolysis of preceramic compounds and to demonstrate how several different fields of research like organoelement chemistry materialss processing and charcaterization can be combined for the development of novel advanced materials.

Polarized electroluminescence from an oriented substituted polythiophene in a light emitting diode

Abstract: Polarized light sources based on stretch-oriented conjugated polymers are reported. The devices, based on poly 3(4-octylphenyl)-2,2′-bithiophene, show an external quantum efficiency of 0.1% and are produced using a very simple method which may be easily extended to other polymers. The fabrication of the devices is described and factors such as the emission and spectral differences parallel and prependicular to the stretching direction discussed.

Stereomutation in optically active regioregular polythiophenes

Abstract: It is shown that stereomutation in thin films of optically active head-to-tail poly[3-(2-[(S)-2-methylbutoxy]ethyl)thiophene] can be observed and modulated via the thermal history of the material. The use of these materials for reversible optical recording is discussed

Lateral deposition of polypyrrole lines by means of the scanning electrochemical microscope

Abstract: Structures of polypyrrole that were laterally deposited with the scanning electrochemical microscope onto conducting substrates from aqueous solutions with non-restricted diffusion properties have been reported for the first time. The polymer lines obtained are predominantly determined by the size of the microelectrode.

Template synthesis of graphitic nanotubules

Abstract: : We describe a method for preparing monodisperse graphitic nanotubules. These are prepared by synthesizing polyacrylonitrile (PAN) from the monomer, within the pores of a porous alumina template membrane. Because the membrane used has cylindrical pores of uniform diameter, monodisperse PAN tubules are obtained. The PAN tubules are then heated to affect graphitization of the PAN. jg p.2

Doped and heteroatom-containing fullerene-like structures and nanotubes†

Abstract: A review of the current knowledge on carbon fullerenes doped with foreign atoms and heteroatom-containing fullerene-like structures and nanotubes is provided Strong covalent bonds lend high specificity and stabilize the hollow-cage and symmetric structure of these moieties These structures are distinct from noble-gas and metallic clusters, where either weak van der Waals forces or stronger metallic bonds, which are not very specific, hold the cluster atoms together In the latter kind of clusters, atoms gain stability through close packing and large coordination numbers and consequently they cannot afford a hollow core Nonetheless some intermetallic nanoparticles exhibit truncated icosahedral symmetry The field is divided, somewhat artificially, into two separate categories One family consists of fullerene-like clusters assembled from different atoms which do not have a bulk counterpart of similar chemical formula The other group is that of fullerene-like nanostructures which are obtained mainly from ubiquitous 2-D layered compounds; various elements and compounds with 3-D character and also from certain metallic alloys It is shown that nanoparticles of 2-D compounds are unstable in the planar form and they reconstruct into hollow-cage nanoparticles, spontaneously Nanosolids of this kind may reveal vastly different properties from their bulk predecessors Numerous applications for the doped and heteroatom fullerene-like materials in the fields of catalysis, lubrication, electronic and photonic devices, alternative energy sources, etc are expected upon further study and development

Sol-gel processing of optical and electrooptical materials

Abstract: ~'I as it has become known, is used by a high and increasing number of materials science researchers because its versatility allows the preparation of a large number of materials. However, it is by no means new. Its origin goes back to early experiments on thin dielectric coatings at Schotti8] in Germany in the early 1970s or the work carried out at the Oak Ridge National Laboratory, USA, and Harwell. Great Britain, with the aim of preparing nuclear ceramic fuels.['- "I This work resulted in the development of the sol-gel process by the end of the 1970s for the processing of advanced ceramic materials and glasses for technological applications and interest has accelerated ever since. The fundamental idea was replacing the classical and ancient high-temperature techniques by a room temperature process based on the possibility of forming a glassy network by polymerization of suitable compounds (monomers) at low teniperaturc. Ideal monomers are molecules which form M-0-M units (M = metal) upon polymerization, and where the reaction byproducts can easily leave the system. Metal alkoxides, M(OR), , fulfil these requirements, where R is an alkyl radical. A popular choice of precursor solution is based on the hydrolysis and polycondensation reactions of metal alkoxides.". 21 Tetramethoxysilane, Si(OCH,),, or tetraethoxysilane, Si(OC,H,),, known as TMOS and TEOS, respectively, are currently used in the preparation of silicabased gels. Since, however, these compounds and water are not miscible, a common solvent (generally, methyl or ethylalcohol) have to be added to obtain an initially homogeneous liquid. The chemical reactions involved are complicated but they can be summarized as shown in Equations 1 and 2.