bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis, processing sand properties of thermotropic liquid‐crystal polymers
Authors: Yoon Hyun N. , Charbonneau Larry F. , Calundann Gordon W. 
Published: December 2004

AbstractThermotropic liquid‐crystal polymers for high‐performance applications are typically based on wholly aromatic polyester and polyamide architectures. The linear character of the aromtic monomers produces polymer chains with stiff, extended conformations. As a result, the chains organize themselves into a nematic melt and readily orient in response to processing flow fields. The close coupling between chain orientation and flow fields produces both a rich variety of materials and a high degree of controllability of their structure and properties (such as the tensile strength, elastic modulus and coefficient of thermal expansion). In this paper, we describe synthetic efforts to develop liquid‐crystal polymer structures and the relationships between chain molecular structure, processing, and properties of this class of polymers in two distinct processing situations: Injection molding and fiber formation. The special importance of the orientational flow field in developing high orientation and excellent mechanical properties will be highlighted.
Particle size control during production of ceramic nitride powders
Authors: Dorn Friedrich W. , Krquse Werner , Schröder Frank 
Published: December 2004

Modern high‐performance ceramics, such as silicon nitride, silicon carbide, and aluminum nitride are manufactured from ceramic powders (see figure) which have to meet sstringent requirements regarding purity and grain size. Control of the grain size during the first steps of the chemical synthesis of the powders is importnat and has been achieved in the manufacture of silicon nitride via silicon diimide, and aluminum nitride via the carbothermal nitridation of aluminum hydroxide. magnified image
Spin Transition Molecular Materials for displays and data recording
Authors: Kahn Olivier , Kröber Jonas , Jay Charlotte 
Published: December 2004

The development of recording media based on molecular spin‐transition (ST) materials is discussed and applications demonstrated for the first time. The figure shows a compound which exhibits an ST and which is based on FeII and 1,2,4‐triazole units. The central FeII ion undergoes an ST at around 210 K which is accompanied by a purple‐white color change. Requirements for future progress are reviewed. magnified image
The Top‐CARL, process: A patterning technique for organic materials
Authors: Leuschner Rainer , Ahne Hellmut , Hammerschmidt Albert , Kolodziej Günter , Nordmann Jens , Schmidt Erwin , Sebald Michael , Sezi Recai 
Published: December 2004

The patterning of organic layer materials is often hindered by the effects of the conditions used to “develop” the resist material, for example high temperatures for strong bases, which attack the substrate. The process described here allows the patterning even of delicate layers of oriented nonlinear optical polymers. The figure shown a patterned polyimide film 115 μm thick. magnified image
Progress toward biologically produced Biodegradable Thermoplastics
Authors: Poirier Yves , Dennis Douglas E. , Nawrath Christiane , Somerville Chris 
Published: December 2004

Genetically‐engineered bacteria which produce biodegradable polymers and copolymers with structures which depend on the culture in which they are kept are receiving increasing attention. Up to 90% of the dry weight of the bacteria can be intracellular granules of the plastic (see Figure), and the properties of the polymers can be controlled by varying the carbon‐based nutrition of the bacteria. Recent advances are reviewed, including the use of plants instead of bacteria. magnified image
Mesophase formation in α‐sexithienyl at high temperature—an X‐ray diffraction study
Authors: Destri Silvia , Mascherpa Marco , Porzio William 
Published: December 2004

The formation of a mesophase in α‐sexithienyl is reported which cannot be identified as either a nematic or smectic phase. On heating, it is also shown that, through careful control of the reaction conditions, crystalline polythiophene comparable in quality with that prepared by electrosynthesis or other synthetic methods can be obtained. The materials are studied using high‐temperature X‐ray diffraction and differential scanning calorimetry. magnified image
Mechanical Alloying of Titanium‐Base Alloys
Authors: Suryanarayana Challipalli , Froes Francis H. 
Published: December 2004

AbstractApplication of mechanical alloying to titanium‐base alloys is a recent development. A wide range of terminal phases and those based on titanium aluminides (both Ti3Al and TiAl) have been examined and it has been shown that synthesis of metallic phases can be achieved by mechanical alloying. The phases so synthesized include solid solutions, intermediate crystalline phases, amorphous phases, and nanostructured materials. It has also been shown that the resistance to coarsening of both the grains and the dispersoids in mechanically alloyed Ti3Al based alloys is much higher than in rapidly solidified alloys. The review concludes with some thoughts on future developments in this exciting area.
Fluorescent sensors and color‐change indicators for molecules
Authors: Ueno Akihiko 
Published: December 2004

Cyclodextrins substituted with a fluorescent group can be employed as molecular sensors. The Figure shows how the fluorophore usually occupies the hydrophobic interior of the cyclodextrin host. On addition of a guest, the fluorophore is displaced from the cavity, resulting in a change in its spectral response. Recent progress with this and related molecular sensors is discussed. magnified image
Ferroelectric Liquid Crystals with an alkanoyl group
Authors: Kobayashi Shogo , Ishibashi Shigeki , Takahashi Kazue , Tsuru Shinji , Yamamoto Fumio 
Published: December 2004

AbstractRecent studies on ferroelectric liquid crystals (FLCs) with an alkanoyl group are reviewed in this article. The FLCs exhibit large spontaneous polarization, especially when another chiral group is introduced at the opposite side of the core. The maximum value reaches 1130 nC/cm2, which is almost the same as the total transverse dipole in the molecule. Fastswitching FLC mixtures can be obtained by using these compounds. The synthesis and properties of FLC polymers having the same mesogen and chiral group are also described, and some applications of the FLC mixtures in devices for optical communication reported.
Overwrite repeatability of GeSbTe phase‐change‐type optical disk media
Authors: Yamazaki Hiroki , Sugiyama Yasuyuki , Chiba Reiichi , Yagi Shougo 
Published: December 2004

Phase‐change‐type erasable optical recording media can be overwritten in a simple process, which should lead to a faster data transfer rate and cheaper optical storage devices. The properties of various protective layer materials for optical disks have been investigated, including their surface flatness (see Figure), reflectivity stability and error modes during repeated overwriting. magnified image magnified image
Microwave absorbing materials based on conducting polymers
Authors: Olmedo Laurent , Hourquebie Patrick , Jousse Franck 
Published: December 2004

Blends of conducting and insulating polymers (e.g. polypyrrole/PVC, see figure) offer distinct weight advantages over the materials, such as dispersions of carbon black or metallic powders in polymer matrices, traditionally used in microwave absorption applications. Polypyrrole, polyaniline, and polythiophene have been examined, their performance parameters compared, and requirements for further development of this technology dicussed. magnified image
Ferromagnetically coupled decamethylmetallocenium salts of 2, 5‐dimethyl‐N,N′‐dicyanoquinonediimine, [M(C5Me5)2]⊕[Me2DCNQI]⊙⊖, (M = Fe, Mn)
Authors: Miller Joel S. , Vazquez Carlos , McLean R. Scott , Reiff William M. , Aumüller Alexander , Hünig Siegfried 
Published: December 2004

Cooperative magnetic interactions in organic materials (such as ferri‐ or ferromagnetic behavior) have been observed in only a few cases. The title compound, shown in the Figure, has been synthesized and represents a further step in the study of structure–function relationships in these materials, from which it is hoped the structures of higher performance materials can be predicted. magnified image
Scanning Acoustic Microscopy—recent applications in materials science
Authors: da Fonseca Raul J. M. , Ferdj‐Allah Lahouari , Despaux Gilles , Boudour Amar , Robert Laurent , Attal Jacques 
Published: December 2004

A convergent beam of ultrasonic waves at very high frequencies can be used in an acoustic microscope to achieve resolutions of the order of 1 μm at depths of up to 1 mm. One application of the acoustic microscope are welding tests (e.g. the Figure which shows an Si/Mo structure welded at 475°C). magnified image
A new method for the production of Mg–Ni hydrogen storage materials
Authors: Li Jinping , Ji Xinfang , Wu Feng , Wang Guoqing 
Published: December 2004

Hydrogen storage materials based on magnesium alloys are interesting because they exhibit light weight, a large hydrogen capacity, and have a low cost. The Figure shows Mg2Ni which has been produced using powder metallurgical methods. It is found to have an attractive property profile compared to material prepared using induction melting. magnified image
Microemulsions and organogels: Properties and novel applications
Authors: Rees Gareth D. , Robinson Brian H. 
Published: December 2004

The phase behavior of surfactant – oil – water mixtures gives rise to a wide variety of possible equilibrium systems, including microemulsions. The Figure shows one model for a gelatin‐containing microemulsion‐based organogel deduced from data from small‐angle neutron scattering. The conditions required and the stability of microemulsions are briefly reviewed before their applications, and the supramolecular architectures they provide, are considered in more detail. magnified image
Calcite crystallization on gelatin films containing polyelectrolytes
Authors: Falini Giuseppe , Gazzano Massimo , Ripamonti Alberto 
Published: December 2004

The promotion of oriented calcie crystallization by various polyelectrolytes, in particular their relative efficiency, has been investigated. Gelatin containing polyelectrolytes was found to overcome the compatibility problem between an inert matrix and the water‐soluble polyelectrolytes as sociated with biomineralization (the Figure shows calctie crystals grown on such a substrate). magnified image
Monocrystalline Si3N4 filaments
Authors: Hüttinger Klaus J. , Pieschnick Torsten W. 
Published: December 2004

In the search for structural materials suitable for high temperatures. monocrystalline silicon nitride filaments have been synthesized by catalyzed chemical vapor deposition. Such a filament with a catalyst particle at the tip is shown in the Figure. The effect of various flow rates of N2/NH3 and H2, the X‐ray emission spectra, and the mechanical properties of the filaments are presented. magnified image
Self‐supporting films of clay minerals and metal oxides: Molecular ceramics
Authors: Isayama Munetoshi , Kunitake Toyoki 
Published: December 2004

Self‐supporting, flexible films of montmorillonite that retain the fundamental characteristics of the mineral have been produced (The Figure shows a cross‐sectional view). This demonstrates that one practical disadvantage of clay minerals‐that they are usually only available as powders‐can be overcome. Further examples of the extension of microscopic layer structures to the macroscopic scale to produce “molecularly defined ceramics” are presented. magnified image
Aerosol‐assisted chemical vapor deposition (AACVD) of silver, palladium and metal alloy (Ag1−xPdx, Ag1−xCux and Pd1−xCux) Films
Authors: Xu Chongying , Hampden‐Smith Mark J. , Kodas Toivo T. 
Published: December 2004

Thermally labile, low‐volatility molecules are usually unsuitable as precursors for the chemical vapor deposition of high‐quality metal films. Here, a new method, aerosol‐assisted CVD (see Fig.), is reported, and used to produce crystalline silver, palladium, and binary metal alloy thin films from just such precursors. magnified image
Fabrication of PbS nanoparticles embedded in a polymer Film by a gas‐aerosol reactive electrostatic deposition technique
Authors: Salata Oleg V. , Dobson Peter J. , Hull Peter J. , Hutchison John L. 
Published: December 2004

Semiconductor nanoparticles embedded in an inert matrix can be seen as a type of quantum‐dot composite, materials which have great potential in optoelectronic applications such as lasers. Room‐temperature electrostatic spraying is used to produce composites based on PbS nanoparticles in a polyvinyl alcohol matrix (e.g. see Fig.) and their potential for application is discussed. magnified image
Polytriacetylenes: Conjugated polymers with a novel all‐carbon backbone
Authors: Schreiber Martin , Anthony John , Diederich François , Spahr Michael E. , Nesper Reinhard , Hubrich Michael , Bommeli Frank , Degiorgi Leonardo , Wachter Peter , Kaatz Phil , Bosshard Christian , Günter Peter , Colussi Martin , Suter Ulrich W. , Boudon Corinne , Gisselbrecht Jean‐Paul , Gross Maurice 
Published: December 2004

New, synthetically accessible, soluble, stable all‐carbon‐backbone polymers are reported. The polytriacetylenes (see Fig.) represent an intermediate step between polydiacetlylenes and carbyne and as such are of interest as alternatives for known conjugated polymers. The synthesis, film casting, and interesting properties are discussed. magnified image
Molecular conductors from neutral heterocyclic π‐radicals
Authors: Cordes A. Wallace , Haddon Robert C. , Oakley Richard T. 
Published: December 2004

Stable radical species (e.g. see Fig.) can form an alternative source of organic conducting materials. Suppressing the Peierls distortion and stabilizing the metallic state can be achieved by applying pressure or by developing materials with enhanced two and three‐dimensional interactions. Recent progress in the synthesis, and stabilization, for example through doping, is discussed. magnified image
Langmuir monolayer assemblies on chemical oscillators
Authors: Yoneyama Mitsuru , Fujii Akiteru , Maeda Shuichi 
Published: December 2004

Oscillatory chemical reactions are exemplified by the Belousov‐ Zhabotinskii (BZ) reaction. A new type of structurally ordered chemical oscillator is reported: the BZ reactor‐Langmuir monolayer coupled system (see Figure), where the monolayer contains Ru(bpy)32⊕ (bpy is bipyridyl), which luminesces. The preparation and spatio‐temporal properties of this system are described. magnified image
Observation of phase‐separated polymeric LB films using scanning probe microscopy
Authors: Yuba Tomoyuki , Yokoyama Shiyoshi , Kakimoto Masa‐Aki , Imai Yoshio 
Published: December 2004

Formation of polyimide films by the Langmuir‐Blodgett (LB) method is described. The preparation and possible applications of the films are detailed. In a mixed LB film of two different polyimides, friction force microscopy reveals hexagonal islands (see Figure), which is the first observation of two‐dimensional phase separation in a polymer mixture. magnified image
The primary steps in photography: Excited J‐aggregates on AgBr Microcrystals
Authors: Trösken B. , Willig F. , Schwarzburg K. , Ehret A. , Spitler M. 
Published: December 2004

The primary process in the photographic emulsion is interfacial electron transfer. The electron is transferred from the excited state of a dye species to empty electron acceptor states in silver bromide. There have been no detailed measurements of the rate constants of this commercially important process. The fluorescence decay curves of thiocarbocyanine dye (see figure) yield these rate constants. magnified image
Exciton band structures in 2D aggregates of cyanine dyes
Authors: Kirstein Stefan , Möhwald Helmuth 
Published: December 2004

Herring‐bone structures (see figure, where the rectangles are the dye molecules and the arrows indicate the oscillation of the transition dipoles) can be classified on the basis of the angle of mutual orientation of the two molecules per unit cell. Those with small angles showing nearly resonant fluorescence emission from the most redshifted transition (J‐aggregates). magnified image
Real space evidence for reversible metal–metal bond rearrangement induced by AFM tip force
Authors: Bengel Hardy , Cantow Hans‐Joachim , Magonov Sergei N. , Whongbo Myung‐Hwan 
Published: December 2004

The reversible rearrangement of weak metal‒metal bonds in layered transition metal chalcogenides is shown to be induced by the force exerted by the tip of an atomic force microscope. The figure shows how the ribbon chains which make up the layers of NbTe2 are reversibly switched by 60° by increasing ad decreasing the force at the tip. magnified image
Aligned carbon nanotubes in a thin polymer film
Authors: Ajayan Pulickel M. 
Published: December 2004

Carbon nanotubes (see figure) constitute one of the smallest one‐dimensional and nearly perfect structures available and these materials should exhibit a wide range of interesting properties. Most of these properties, however, will only be of use if te structures can be manipulated into a controlled configuration here the alignment of nanotubes in thin polymer films is discussed. magnified image
Present limits of data storage using dye molecules in solid matrices
Authors: Ao Rong , Kümmerl Lothar , Haarer Dietrich 
Published: December 2004

Optical data storage offers the potential advantages of high storage densities, fewer mechanical problems, low reading and writing energies, ruggedness, and higher data rates. Currently, the only true photonic optical storage medium is the spectral hole burning scheme. The features of the technique are presented, the materials (e.g. see figure) and necessary laser technology presented, and a view is given of the prospects and requirements for future commercial development. magnified image
Unsaturated ladder polymers: Structural variations and improved molecular weights
Authors: Schlicke Benediki , Schirmer Heike , Schlüter Arnutlf‐Dieter 
Published: December 2004

All‐carbon ladder polymers with extended π systems are of interest for electroluminescence and photovoltaics applications. The synthesis of two new ladder polymers (e.g. see Figure) exhibiting relatively high molecular weights and pronounced film‐forming abilities, is reported. It is also shown that the degree of saturation in these polymers can be chemically closly controlled. magnified image
Triplet radical pairs of 3‐carboxyproxyl encapsulated in a dendritic box
Authors: Meijer E. W. , Jansen Johan F. G. A. , Janssen René A. J. , de Brabandero‐van den Berg Ellen M. M. , Meijer E. W. 
Published: December 2004

The encapsulation of small molecules inside a dendrimeric “box” has recently been reported. Here, the encapsulation and mobility of triplet radical moieties is described. For “boxes” (e.g. see Figure) containing two or more radicals the intermolecular ferromagnetic alignment of the encapsulated radicals to triplet state radical pairs is observed. magnified image
A new class of electron transport compounds: 1,3‐bis‐dicyanomethylene indanes
Authors: Rommens Johan , van der Auweraer Mark , De Sclryver Frans C. , Borsenberger Paul M. 
Published: December 2004

Electron transport layers, comprised of polymers doped with electron acceptor compounds have proved difficult to develop as teh inclusion of the acceptors generally results in poor solubility in coating solvents, limited miscibility and even toxic properties. The title compounds (see Figure) are soluble, miscible with a wide range of polymers, and show essentially to absorption in the visible region of the spectrum. magnified image
Shadowed sputtering of gold on V ‐shaped microtrenches etched in silicon and applications in microfabrication
Authors: Xia Younan , Whitesides George M. 
Published: December 2004

Silicon micromachining has a wide range of applications in, for example, microelectronics. Here, a combination of several techniques is used in modifying the surface properties of V‐shaped microtrenches (see Figure) and for fabricating complex surface relief structures. magnified image
Partial specific volumes of synthetic polypeptides in dilute solution
Authors: De Loźe C. , Saludjian P. , Kovacs A. J. , Schermutzki B. 
Published: December 2004

AbstractWe report a simple method for measuring partial specific volumes, of polymers in dilute solutions with an accuracy of 3 parts per thousand. This method has been applied to 7 polypeptides in 4 organic solvents. The residue volumes deduced from these data are compared to those calculated by a differential method. The discrepancy is generally of the order of 1.5%.
On the theory of order‐disorder transition and copolymer structure of DNA
Authors: Lifson Shneior , Allegra Giuseppe 
Published: December 2004

AbstractThe statistical mechanical theory of the helix‐coil transition of DNA has been recently discussed by one of the authors, who considered an assembly of DNA molecules with a Markoff distribution of nucleotide sequences. The present communication improves upon the above mentioned theory by introducing approximate normalization factors for the unnormalized statistical weights of finding a given molecule of the assembly in a given microscopic state.
Synthesis of tritiated poly‐L‐lysine (γ, δ‐T2)
Authors: Fridkin M. , Sokolovsky M. , Katchalski E. 
Published: December 2004

AbstractTritiated poly‐L‐lysine (γ, δ‐T2) (IX) was prepared according to the following procedure: Tritiated DL‐lysine (γ, δ‐T2) (III) was derived from acetamino‐(‐4‐amino‐Δ2‐butenyl)‐diethylmalonate (I) by tritiation followed by acid hydrolysis. The racemic tritiated lysine was converted to its ε, N‐trifluoroacetyl derivative IV, and the latter resolved via its chloroacetyl derivative by means of hog kidney acylase. The optically active tritiated ε, N‐trifluoroacetyl‐L‐lysine (VI) was converted into the corresponding N‐carboxyanhydride VII with phosgene, and polymerization carried out in dioxane using triethylamine as initiator. The required tritiated poly‐L‐lysine (IX, n = 250) was obtained from the blocked polymer VIII after removal of the protecting groups with piperidine. The tritiated polypeptide possessed an activity of 250 mC. per mmole lysine residue. The procedure described enables, however, the preparation of poly‐L‐lysine with up to 25 times higher specific activity.
Polarographic reducibility of denatured DNA
Authors: Paleček E. , Vetterl V. 
Published: December 2004

AbstractThe de polarographic behavior of native and denatured DNA at pH 7.0 was studied. Whereas native DNA was polarographically inactive under the given conditions, denatured DNA yielded a reduction polarographic step at the potential of about −1.4 V. Native DNA produced a single desorption wave on ac polarograms, while denatured DNA yielded, in addition to this wave, another more negative wave approximately corresponding, as to its potential, to the dc polarographic step of denatured DNA. The behavior of apurinic acid was similar to that of denatured DNA. The course of DNA denaturation at elevated temperature was studied by means of the two above techniques and changes at temperatures below the melting temperature observed. This finding is in agreement with earlier results obtained by oscillopolarographic and the pulse‐polarographic method.