Radiation Induced Structural And Motional Changes Occurring In Silica Filled Silicone Polymer Foams As Probed By Multinuclear Nmr
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| Release | : 1999 |
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The aging of polymeric composite materials through factors such as thermal and mechanical stresses, environment, radiation, and chemical attack can affect the length of time for which a given material can maintain its engineering performance. Iterative interactions and cumulative reactions may result in the material or device reaching a critical age where its properties fail unexpectedly and catastrophically. The mechanical property changes associated with multi-mechanism aging may be subtle, and may not necessarily change linearly as a function of time in service. Since such linear relationships are often used in lifetime predictions, there is a fundamental need to develop and employ spectroscopic methods to investigate the structural and motional changes that occur in these organic-inorganic materials as a result of aging in chemically, thermally, or radioactively harsh environments. Silica filled polydimethylsiloxane (PDMS) composite systems are of technological interest due to their chemical and environmental resilience. Silica is usually chosen as the filler phase due to the significant reinforcement of the composite material through hydrogen bonding between the polymer chains and the surface groups on the filler. Unfilled PDMS is known to crosslink when exposed to high-energy radiation. The presence of a silica filler phase, which has a higher electron density than the polymer matrix, has been proposed to result in an increased incidence of crosslinking or scission due to backscatter of the incident radiation. Cohen-Addad has used 1H relaxation times to characterized cross-link density in unirradiated filled PDMS and Charlesby has reported 1H relaxation studies of irradiation induced changes in unfilled PDMS systems of average molccular weights up to 1 MDalton. However, no specific studies have been reported on aging of silica-filled PDMS based polymers systems. To this end the authors have applied Nuclear Magnetic Resonance (NMR) methods to gain insight into the processes that are contributing to mechanical failure of silica filled polydimethylsiloxane (PDMS) based cushions. The studies so far have concentrated on (A) 1H, 13C, and 29Si Magic Angle Spinning (MAS) measurements of chemical speciation from chemical shifts, and (B) 1H relaxation measurements.
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| Release | : 2000 |
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The aging of polymeric composite materials, such as filled polydimethylsiloxane foams, through factors such as thermal and mechanical stresses, environment, radiation, and chemical attack can affect the length of time for which a given material can maintain its engineering performance. Iterative interactions and cumulative reactions may result in the material or device reaching a critical age where its properties fail unexpectedly and catastrophically. The mechanical property changes associated with multi-mechanism aging may be subtle, and may not necessarily change linearly as a function of time in service. Since such linear relationships are often used in lifetime predictions, there is a fundamental need to develop and employ spectroscopic methods to investigate the structural and motional changes that occur in these organic-inorganic materials as a result of aging in chemically, thermally, or radioactively harsh environments. We have used multinuclear nuclear magnetic resonance (NMR) spectroscopy to characterize aging signatures in a series of PDMS based composite materials. Unfortunately, 13C, 29Si, and 1H magic angle spinning NMR spectra remain unchanged with gamma radiation exposure up to 50Mrad. This suggests that the speciation related changes are small and occur at a frequency of less than approximately 1% of the monomer units. As a result, we have shifted focus and have employed relaxation studies to monitor changes in motional properties of the copolymer foams caused by irradiation. We have measured spin-lattice, spin-spin, and rotating frame spin-lattice relaxation times for PDMS model rubbers with variable cross link density and filler content, for M9760 foams irradiated from 0 to 50Mrad, and for dehydrated M9760 foams. Spin-lattice relaxation times, in general, are sensitive to fast molecular motions in the MHz frequency range. Spin-spin and rotating frame relaxation times, on the other hand, are sensitive to changes in slower motion processes in the kHz range. Comparison of changes in these relaxation parameters in the irradiated samples to mechanical properties, cross-link density, and filler content dependencies observed in the model compounds have lead to a picture of the changes in motional properties of the foam due to irradiation and water content. The characterization of motional changes in the foams could provide important data for predictive modeling efforts. In addition, we have also developed empirical relationships between relaxation times and interfacial and bulk polymer motional properties that might allow rapid NMR based screening methods to compliment solvent swelling experiments.
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| Total Pages | : 756 |
| Release | : 2000 |
| Genre | : Textile fabrics |
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| Author | : The Nuclear Magnetic Resonance Society of Japan |
| Publisher | : Springer |
| Total Pages | : 634 |
| Release | : 2017-11-23 |
| Genre | : Science |
| ISBN | : 9811059667 |
This book describes the advanced developments in methodology and applications of NMR spectroscopy to life science and materials science. Experts who are leaders in the development of new methods and applications of life and material sciences have contributed an exciting range of topics that cover recent advances in structural determination of biological and material molecules, dynamic aspects of biological and material molecules, and development of novel NMR techniques, including resolution and sensitivity enhancement. First, this book particularly emphasizes the experimental details for new researchers to use NMR spectroscopy and pick up the potentials of NMR spectroscopy. Second, the book is designed for those who are involved in either developing the technique or expanding the NMR application fields by applying them to specific samples. Third, the Nuclear Magnetic Resonance Society of Japan has organized this book not only for NMR members of Japan but also for readers worldwide who are interested in using NMR spectroscopy extensively.
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| Total Pages | : 36 |
| Release | : 2008 |
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Radiation induced degradation of polymeric materials occurs via numerous, simultaneous, competing chemical reactions. Though degradation is typically found to be linear in adsorbed dose, some silicone materials exhibit non-linear dose dependence due to dose dependent dominant degradation pathways. We have characterized the effects of radiative and thermal degradation on a model filled-PDMS system, Sylgard 184 (commonly used as an electronic encapsulant and in biomedical applications), using traditional mechanical testing, NMR spectroscopy, and sample headspace analysis using Solid Phase Micro-Extraction (SPME) followed by Gas Chromatography/Mass Spectrometry (GC/MS). The mechanical data and 1H spin-echo NMR indicated that radiation exposure leads to predominantly crosslinking over the cumulative dose range studies (0 to 250 kGray) with a rate roughly linear with dose. 1H Multiple Quantum NMR detected a bimodal distribution in the network structure, as expected by the proposed structure of Sylgard 184. The MQ-NMR further indicated that the radiation induced structural changes were not linear in adsorbed dose and competing chain scission mechanisms contribute more largely to the overall degradation process in the range of 50 -100 kGray (though crosslinking still dominates). The SPME-GC/MS data were analyzed using Principal Component Analysis (PCA), which identified subtle changes in the distributions of degradation products (the cyclic siloxanes and other components of the material) as a function of age that provide insight into the dominant degradation pathways at low and high adsorbed dose.
| Author | : Masami Okamoto |
| Publisher | : iSmithers Rapra Publishing |
| Total Pages | : 190 |
| Release | : 2003 |
| Genre | : Science |
| ISBN | : 9781859573914 |
The review sets out to highlight the major developments in this field over the last decade. The different techniques used to prepare PLS nanocomposites are covered. The physicochemical characterisation of PLS nanocomposites and the improved materials properties that those materials can display are discussed. An additional indexed section containing several hundred abstracts from the Rapra Polymer Library database provides useful references for further reading.
| Author | : Victor M. Litvinov |
| Publisher | : iSmithers Rapra Publishing |
| Total Pages | : 666 |
| Release | : 2002 |
| Genre | : Science |
| ISBN | : 9781859572801 |
This book deals with the application of spectroscopic techniques for characterisation of chemical and physical structures in viscoelastic materials, such as unvulcanised elastomers and their vulcanisates, various rubbery materials and some plastics, which when blended with particular additives (plasticisers) behave like rubbers. Analysis of the rubbery materials is complicated by the fact that rubbery products, such as tyres, tubes, seals, V-belts and hoses, contain in the rubbery matrix a significant amount of various compounds, i.e., fillers, vulcanising agents, antioxidants and plasticisers. Due to the complex composition, no single technique can provide a good understanding of the effect of chemical and physical structures on the functional properties of rubbery materials. Thus spectroscopy has become a powerful tool for the determination of polymer structures. The most comprehensive information on chemical and physical structures in relation to material properties can be obtained by using a combination of macroscopic techniques and methods that provide information on the molecular level. frequently used for analysis of rubbery materials, i.e., various methods of nuclear magnetic resonance (NMR) and optical spectroscopy. The main objective of this present book is to discuss a wide range of applications of the spectroscopic techniques for the analysis of rubbery materials. The book brings together the various spectroscopic techniques for obtaining the following information: chemical structure of rubbery materials, network structure analysis, heterogeneity of rubbery materials, physical properties of rubbery materials, functional properties and stability of rubbery materials, processing of rubbery materials and quality control. The contents of this book are of interest to chemists, physicists, material scientists and technologists who seek a better understanding of rubbery materials.
| Author | : Susannah L. Scott |
| Publisher | : Springer Science & Business Media |
| Total Pages | : 341 |
| Release | : 2008-04-06 |
| Genre | : Science |
| ISBN | : 0387306412 |
With the recent advent of nanotechnology, research and development in the area of nanostructured materials has gained unprecedented prominence. Novel materials with potentially exciting new applications are being discovered at a much higher rate than ever before. Innovative tools to fabricate, manipulate, characterize and evaluate such materials are being developed and expanded. To keep pace with this extremely rapid growth, it is necessary to take a breath from time to time, to critically assess the current knowledge and provide thoughts for future developments. This book represents one of these moments, as a number of prominent scientists in nanostructured materials join forces to provide insightful reviews of their areas of expertise, thus offering an overall picture of the state-- the art of the field. Nanostructured materials designate an increasing number of materials with designed shapes, surfaces, structures, pore systems, etc. Nanostructured materials with modified surfaces include those whose surfaces have been altered via such techniques as grafting and tethering of organic or organometallic species, or through various deposition procedures including electro, electroless and vapor deposition, or simple adsorption. These materials find important applications in catalysis, separation and environmental remediation. Materials with patterned surfaces, which are essential for the optoelectronics industry, constitute another important class of surface-modified nanostructured materials. Other materials are considered nanostructured because of their composition and internal organization.
| Author | : Chinnappan Baskar |
| Publisher | : Springer Science & Business Media |
| Total Pages | : 484 |
| Release | : 2012-05-08 |
| Genre | : Technology & Engineering |
| ISBN | : 3642284183 |
The consumption of petroleum has surged during the 20th century, at least partially because of the rise of the automobile industry. Today, fossil fuels such as coal, oil, and natural gas provide more than three quarters of the world's energy. Unfortunately, the growing demand for fossil fuel resources comes at a time of diminishing reserves of these nonrenewable resources. The worldwide reserves of oil are sufficient to supply energy and chemicals for only about another 40 years, causing widening concerns about rising oil prices. The use of biomass to produce energy is only one form of renewable energy that can be utilized to reduce the impact of energy production and use on the global environment. Biomass can be converted into three main products such as energy, biofuels and fine chemicals using a number of different processes. Today, it is a great challenge for researchers to find new environmentally benign methodology for biomass conversion, which are industrially profitable as well. This book focuses on the conversion of biomass to biofuels, bioenergy and fine chemicals with the interface of biotechnology, microbiology, chemistry and materials science. An international scientific authorship summarizes the state-of-the-art of the current research and gives an outlook on future developments.
| Author | : K. Nagata |
| Publisher | : Springer Science & Business Media |
| Total Pages | : 261 |
| Release | : 2013-12-11 |
| Genre | : Science |
| ISBN | : 4431669701 |
The metabolism of all living organisms consists of elaborate and complex interactions among numbers of biomolecules, including protein-protein interactions. BIACORE is a new device that uses surface plasmon resonance for kinetic analysis of molecular interactions and automates whole analytical processes. The number of users of BIACORE is increasing worldwide, but until now nothing had been published in English to explain the principles of this new methodology and the kinds of applications it makes available. This updated and revised version of the Japanese original explains the underlying principles of BIACORE, providing concrete examples that utilize the methodology for analysis in areas ranging from basic to applied sciences. With its generous use of illustrations, this book is a valuable source of information for all users of BIACORE.
