			Home About us Contact

Properties Modification (property + modification)

Distribution by Scientific Domains

Physics and Astronomy	40%
Chemistry	40%

Selected Abstracts

Properties modification of PET vascular prostheses

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 5 2009
W. Chaouch
Abstract Aging mechanisms have been investigated on polyethylene terephthalate (PET) fibres extracted from various vascular prostheses in order to identify the different modifications of the material's degradation. NMR spectroscopy provides a comprehensive view of chemical structures of macromolecules. Examination of a series of PET fibres showed significant chemical differences between the virgin prostheses and the explants, especially for diethylene glycol (DEG) and cyclic oligomeric groups. These analyses revealed that PET failures in vascular prostheses are susceptible to hydrolysis during in vivo stay. We also extended this 1H NMR technique to determine the hydroxyl and carboxyl end-group concentrations. In order to validate the 1H NMR results, complementary techniques , chemical titration and classical viscosimetry , were used. The obtained results showed an increase in end-group concentrations and a decrease of the viscosity averaged macromolecular weight (M,) for the explants. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Laser fluence and shot number dependence of laser-induced optical properties modification of transparent materials

LASER PHYSICS LETTERS, Issue 12 2006
K. Jamshidi-Ghaleh
Abstract Micro-fabrication in transparent materials by femtosecond laser-induced modification of the optical properties inside transparent materials, preferentially optical glasses, has received much attention. Ultra short laser pulses are capable of inducing these modifications without cracking or even melting the glasses. This kind of modification, which appears as darkening inside glass relates to the trapped electrons or holes at defect sites in the glass matrix. The femtosecond laser technology allows controlling and modifying the optical properties of glasses on a sub-micrometer scale. Laser fluence and laser shot number are important parameters for femtosecond laser-induced modification of glasses. This paper presents the 800 nm femtosecond laser-induced optical modification inside soda lime glasses at different laser fluence levels and laser shot numbers. Modification thresholds at different applied laser fluences and shot numbers are measured. Pulse energy accumulation model is proposed to predict the behaviour of darkened area spots with applied laser fluence and shot numbers. Our experimental results and the pulse energy accumulation model are in good agreement. (© 2006 by Astro, Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source]

Properties of MBE CdxHg1,xTe/GaAs structures modified by ion-beam milling

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2004
V. V. Bogoboyashchyy
Abstract Modification of electrical properties of n - and p -type MBE mercury,cadmium-telluride (MCT) structures with passivation gradient band gap layers under ion milling was investigated. Main features of the CdxHg1,xTe electrical properties modification with such treatment also hold for MBE MCT structures in comparison with bulk samples. It is shown that a significant decrease of the p,n conversion rate for such structures in comparison with homogeneous bulk samples at other equal conditions is caused by the presence of the wide band gap passivation layer. The diffusion-like character of the p,n conversion front movement is confirmed. The nature of additional "heavy" electrons in MBE structures is proposed. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Dendrimers: a review of their appeal and applications,,

JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 9 2001
Graham M Dykes
Abstract Dendrimer chemistry is one of the most fascinating and rapidly expanding areas of modern chemistry. This review attempts to uncover the appeal of these structurally-perfect branched macromolecules. The three intriguing regions of a dendritic molecule are discussed: the multifunctional surface, the tailored sanctuary within the branches, and the encapsulated core. The advantages of dendritic structures for property modification, and their potential applications in very diverse areas are illustrated. The exciting merger of dendrimer chemistry with self-assembly offers new, stimulating avenues for exploration. Consequently, self-assembling dendrimers comprise a major section of this article. © 2001 Society of Chemical Industry [source]

Poly(vinyl chloride) on the way from the 19th century to the 21st century

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 3 2004
D. Braun
Abstract Despite all the technical and economic problems and the public discussions on the environmental dangers and hazards of chlorine chemistry, poly(vinyl chloride) (PVC) is the second most produced plastic (with a worldwide capacity of about 31 million tons), placing after polyolefins and before styrene polymers. Presently, PVC production worldwide is growing at a rate of more than 4% per year. The application of PVC was first described in a patent in 1913, but only after 1930 did a sustained interest in PVC arise in several industrial laboratories. The most remarkable milestones in PVC history and their importance to the development of macromolecular chemistry are briefly described, and some present PVC research and industrial applications, with respect to polymerization, stabilization, bulk property modification, and chemical and material recycling of PVC waste, are discussed. Some actual selected topics include the emulsion polymerization of vinyl chloride with polymeric surfactants and controlled free-radical polymerization with nitroxyls, whereas ionic and metal organic initiators have not found any technical applications. Chemical reactions offer many possibilities for the modification of PVC, but they have been not used on a technical scale yet. Much work has been done on stabilization with nontoxic or metal-free systems. The bulk properties of PVC can be influenced by impact modification through the addition of graft copolymers or by blending with other polymers. Also presented are some problems and recent developments in PVC recycling. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 578,586, 2004 [source]