Showing papers in "Advanced Materials in 1989"

Generation of complex Metal Oxides by Aerosol Processes: Superconducting ceramic particles and films

Abstract: Complex metal oxides, including ferroelectric, ferrimagnetic and superconducting ceramics, have a variety of technologically useful properties that can be exploited for a number of applications. Fabrication of complex metal oxide ceramics with specific properties requires high-purity powders with controlled chemical compositions, size distributions, and morphologies. Powders with these characteristics can be produced by aerosol processes in which fine particles are generated in gaseous flow systems. The particles can also be deposited from the gas phase onto surfaces to form films. This paper will discuss the use of aerosol processes for the generation of complex metal oxide powders. A review of aerosol processes will be presented first, followed by a discussion of the methods used for the generation of superconducting ceramic powders. Examples include the production of YBa2Cu3O7, La1.85Sr0.15CuO4, and Tl-Ca-Ba-Cu-O powders and films. Emphasis will be placed on defining the conditions required for the generation of chemically homogeneous particles with controlled morphologies.

Modelling Organic Surfaces with Self-Assembled Monolayers

Abstract: : The interfacial properties of organic materials are of critical importance in many applications, especially the control of wettability, adhesion, tribology, and corrosion. The relationships between the microscopic structure of an organic surface and its macroscopic physical properties are, however, only poorly understood. This short review presents a model system that has the ease of preparation and the structural definition required to provide a firm understanding of interfacial phenomena. Long-chain thiols, HS(CH2)nX, adsorb from solution onto gold and form densely packed, oriented monolayers. By varying the terminal functional group, X, of the thiol, organic surfaces can be created having a wide range of structures and properties. Keywords: Self assembly, Monolayers, Thiols, Gold, Organic surfaces.

Liquid Crystalline Elastomers

Abstract: Today, material science is directed towards the development of multifunctional and oriented structures. One example of such supramolecular systems are liquid crystalline (LC) elastomers which combine the properties of LC phases (the combination of order and mobility) with rubber elasticity, one of the most typical polymer properties. Their most outstanding characteristic is their mechanical orientability; strains as small as 20% are enough to obtain a perfectly oriented LC monodomain. This orientability, if LC elastomers with chiral phases are used, leads, for example, to elastomers with chiral smectic C* phases which are likely to show piezo-electric behavior.

The Keviar Story—an Advanced Materials Case Study

Abstract: Limited space permits description of only two examples of Kevlar applications research. There are numerous others. In the early product development there were some indications that Kevlar would go mainly into tire reinforcement. This has turned out not to be true. In the mid-seventies Kevlar was participating in only ten market segments and less than fifty specific applications, but today, it is in more than twenty market segments, serving more than two hundred applications, and continued growth is anticipated. Kevlar is produced in a 45 million pound plant in Richmond, VA, USA. In 1988, a second plant was started up in Northern Ireland and plans for a third plant in Japan were announced. The Kevlar innovation story exemplifies the kind of obstacles, interdisciplinary skills and systems approach involved in bringing a laboratory discovery to commercial reality. The story is still unfolding and applications currently not envisioned will undoubtedly become important in the future. .

Functionalized Conducting Polymers—Towards Intelligent Materials

Abstract: Organic conjugated polymers and oligomers constitute a three-dimensional network of molecular wires, in which all monomeric units can be functionalized with various prosthetic groups. By varying the nature of these groups, specific interactions with external physical or chemical phenomena can be developed in these materials, leading to molecular devices such as sensors, transducers, memories and logic operators. Chemists have already mastered the realization of many of these functional elements, which mimic those existing in organized beings. The further assembly of these elements in multifunctionalized organic conducting polymers and oligomers will represent the next step towards intelligent materials.

Dichroic dyes, and liquid crystalline side chain polymers†

Abstract: Functional guest molecules incorporated into LC-side-chain polymers lead to polymeric materials which combine the physical and optical anisotropic properties of liquid crystals with the special functions of the guest components. This contribution focused on dichroic dyes, but the results are transferable to other guest moieties. The covalent fixation of the dye to the polymer backbone affords several advantages. Liquid crystalline materials with high dye concentrations were obtained opening the way to the preparation of highly ordered, optical uniaxial films with adjustable thickness and optical density. Thin well aligned LC-polymer films can in principle be used as an active medium for reversible optical information storage and mixtures of dye-containing copolymers in low molar mass liquid crystals can be used in displays. Current developments in the area of ferroelectric chiral smectic-C side-chain polymers will further enhance interest in this area.

Structure of anodic oxide coatings on aluminum

Abstract: Etude par des techniques de diffraction de neutrons et de rayons X des couches poreuses amorphes formees par oxydation anodique de feuilles d'aluminium dans H 2 SO 4

Polymer optical fibers and nonlinear optical device principles

Abstract: Basic principles of the present optoelectronic research activities at Hoechst AG are presented in this contribution. Within the diversified broad band spectrum of optoelectronic materials and applications our interest is focused on new types of polymer optical fibers and nonlinear optical device principles using organic Langmuir–Blodgett films and electrically poled polymers. The basic principles and the limits of the present research and development activities which, have a high market potential are outlined.

Polysilanes—a new look at some old materials

Abstract: In spite of the fact that the first polysilane derivatives were probably prepared in the mid 1920's, there was little scientific interest until recently. The synthesis of the first soluble homo and copolymers about 10 years ago has stimulated an explosive development of this class of materials. This brief review traces the historical development of the polysilanes and focuses on recent studies of polymer structure, electronic properties, photochemical reactions and mechanisms and finally on new applications.

Aerospace materials research opportunities

Abstract: As we approach the second century of aerospace, increased emphasis is being placed on endurance, reliability, ease of manufacture, and lower cost, in addition to weight saving. This change in emphasis will have a major effect on not only the selection of materials, but on how materials are integrated into the total system design process. Subsonic aircraft will continue to play a major role in our future with emphasis on increased durability and lower cost. Non-metals that do not corrode are attractive; however, the issues of reliable fracture resistance to ensure safety and durability as well as ease of manufacture and inspection will be key. Higher performance engines and hypersonic aircraft will require higher temperature materials (including a substantial amount of non-metals) along with reliable toughness and ease of manufacture. In space, weight will continue to be a major driving force along with the need for long term vacuum and radiation stability. Ease of assembly and multifunctional use (e.g. electrically or thermally conducting structure) will be additional needs for spacecraft materials. We have reached a point in the evolution of structural materials where we are moving away from processing naturally occurring materials toward synthesizing designed microstructures to perform specific functions. The mathematical modeling of microstructure–property relationships and new chemical and biotechnical synthesis techniques appear to be critical technologies for the future. In addition, the future materials developer will need a broader understanding of the total structural life cycle so that the impact of utilization, maintenance, and training requirements in the design of new materials can be considered.

Magneto‐Optical Recording and Data Storage Materials

Abstract: Amorphous rare-earth (RE) transition-metal (TM) alloys are used for magneto-optical (MO) recording a rapidly developing technology, which combines the possibility of achieving high bit densities with practically unlimited erasability and rewritability. During the last years new insights, relating material properties to recording performance, have been obtained. New experimental techniques, such as the observation of magnetic contrast in the electron microscope, have made a major contribution to the understanding of domain formation processes. The RE-TM alloys have been most successful in recording applications until now. In these materials the RE-TM composition determines both the compensation and Curie temperatures and has a strong impact on the recording characteristics. Improvements in deposition techniques and the application of dielectric layers resulted in carrier-to-noise ratios of 61 dB. Despite major improvements, problems related to corrosion and structural relaxation, which lead to long-term instabilities, have not yet been solved completely. Another important topic is the so-called direct-overwrite problem, which will be discussed in relation to the material properties.

Monolayers and Langmuir–Blodgett multilayers of discotic liquid crystals?

Abstract: The field of monolayer and multilayer films of discotic LCs is at its very beginning. The scope and limitations of this preparation method have not yet been explored, and little is known about the structures obtainable. However, the potential access to extraordinary, ordered thin films is fascinating, and will stimulate research in the future.

Structural characterization of non‐oxide Chalcogenide Glasses using solid state NMR

Abstract: In spite of the long-standing importance of non-oxide chalcogenide glasses in infrared optics and semiconductor technology, concepts describing the structural principles governing glass formation in these systems are just emerging. Most recently, modern quantitative solid state NMR techniques have offered new unique insights into the structural organization of these systems. In this review, we discuss the basic principles of various experimental approaches and their application to boron-silicon,- and phosphorus chalcogenide glasses.