Showing papers in "Advanced Materials in 1991"

Template synthesis of polymeric and metal microtubules

Abstract: : We describe in this report an elegant new method for the synthesis of organic microtubules. This new method is based on the use of a microporous membrane as a template during tubule synthesis. This template method produces tubules with monodisperse lengths and diameters, and length, diameter, and wall thickness can be varied at will. This type of precise control over tubule geometry is not possible with the existing synthetic method. The tubules obtained are composed of chemically and mechanically robust heterocyclic polymers. We have recently described a template method for the synthesis of organic microtubules. This method entails the use of the pores in a microporous membrane as templates for tubule formation. The key to the tubule-formation process is the presence of molecular anchors on the pore walls. These anchors insure that the tubule-forming materials deposits as a thin skin which lines the pore wall. We describe in this paper an electrochemical template method for the synthesis of metal (Au) microtubules. We also present a general paradigm for the formation of molecular anchors on the pore walls of alumina template membranes. We believe that this paradigm should allow for the synthesis of microtubules composed of any desired material.

Designing Luminescent Materials

Abstract: Over the last fifty years, there has been a large research effort in the field of luminescent materials. Such materials find application in, for example, fluorescent lamps, T.V. sets or X-ray detectors. The phosphors applied in such devices are generally inorganic solid-state materials, with an ionic lattice. Research has pushed the luminescence properties of these materials to the physical limits and probably no new classes of these conventional materials, performing equally well or even better, are likely to be found. As a result, the number of conventional phosphor materi- als is not expected to grow further. This has resulted in a change in research strategy. Instead of looking for new 'con- ventional' phosphor materials, research has concentrated on controlling the materials properties of phosphor systems, such as their hygroscopic nature or morphology. In recent years, new inpetus has been given to research dealing with luminescent materials through the application of organic and inorganic cage compounds, the use of organic ligands leading to extremely strong UV absorption, or very small particles exhibiting quantum size effects."] In this paper, we outline some of the activities within Philips research, dealing with these topics.

Decamethylmanganocenium tetracyanoethenide, [Mn(C5Me5)2]..+[TCNE].- - a molecular ferromagnet with an 8.8-K TC

Abstract: Communication Triplet electron- transfer salts are predicted to exhibit bulk ferromagnetic behavior at higher temperatures than their singlet analogues. To test this expected trend, the title compound, which is isostructural with [FeCp 2 ] ⊙⊕ [TCNE] ⊙⊖ (Cp* = pentamethylcyloopentadienide; TCNE = tetracyanoethylene) which exhibits a Curie temperature, T c , of 4.8 K has been synthesized. The synthesis and magnetic characterization of the new compound, which is found to have a T c of 8.8 K, are reported.

Ultrathin organic films: Molecular Architectures for advanced optical, electronic and bio‐related systems

Abstract: Ultrathin ordered organic films with a thickness of a few nanometers to about a tenth of a micrometer show considerable technological potential as a novel class of materials. Of particular interest are their tailor-made electrical and optical properties which are related to their anisotropic molecular structure which itself can be controlled on a molecular scale. A. critical review is given of the different aspects of the potential technological applications of ultrathin organic films. Some underlying chemical concepts and the basic problems to be solved in synthesis and preparation prior to application are discussed.

Preformed polymers for Langmuir–Blodgett films– molecular concepts

Abstract: The use of preformed polymers for the preparation of Langmuir-Blodgett (LB) multilayers is reviewed. Principles for polymer self-organization are outlined and the appropriate molecular designs are discussed. Recent developments in the different classes of polymers for LB multilayers are presented, and their outstanding properties highlighted.

A novel combustion synthesis of spinel ferrites, orthoferrites and garnets

Abstract: A combustion approach for an instant synthesis of fine particle spinel ferrites, orthoferrites and yttrium iron garnet *YIG) is reported. It involves the combustion of redox mixtures containing corresponding metal nitrates and tetraformal trisazine, $C_4H_{16}N_6O_2$ (TFTA) or oxalic acid dihydrazide, $C_4H_{16}N_6O_2$ (ODH) at $350 ^oC$. The process yields homogeneous single-phase fetrrites in less than 5 minutes.

Langmuir–Blodgett membranes for separation and sensing

Abstract: The current status of Langmuir–Blodgett (LB) films is described with regard to biomimetic applications as separating membranes and sensor layers. In the first part, recent research activities on the utility of LB membranes for gas separation, liquid permeation, hyper- and ultrafiltration are reviewed. The morphological aspects of materials separation in LB films are discussed. In the second part, recent progress in the rapidly growing field of LB-film-based chemical sensors and blosensors is reviewed. The structure and function of gas and ion sensors, and enzyme and immunosensors is briefly discussed. Perspectives for future activities in the fields of LB membranes and sensors are outlined.