Download or read book A Molecular Dynamics Investigation of the Mechanism of Turbulence Modification by Polymer Additives and Noise Irradiation written by C. J. Montrose and published by . This book was released on 1987 with total page 36 pages. Available in PDF, EPUB and Kindle. Book excerpt: Molecular dynamics computer simulation experiments have been carried out to study the response of a dilute short-chain polymer solution subjected to severe flow conditions. Under high amplitude shear flows the polymer molecules were observed to reorient and reconfigure so as to be confined to a plane parallel to the flow direction. Once this situation is achieved, aperiodic cycling between coiled and elongated forms within the plane was observed. No significant enhancement of the intramolecular oscillations was seen, nor was there any flow-induced tension developed in the molecule. Conversely, in a configuration in which one end of the molecule was anchored and a uniform flow of solvent was maintained, scission of an intramolecular bond was found at high solvent flow velocities. The mechanism of bond rupture arose from the flow-driven excitation of intramolecular vibrational modes of motion of the molecule, the steady-state tension arising from viscous drag on the molecule being much smaller than that required for bond scission. Analysis of the flow-induced vibrations leads to the conclusion that bond breaking occurs only when there is substantial excitation of the low frequency acoustical modes of the molecule. This mechanism should also be operative in the degradable of very long-chain polymers in a flow field characterized by an extesional velocity gradient.

Download or read book Applied Mechanics Reviews written by and published by . This book was released on 1994 with total page 390 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Technical Reports Awareness Circular TRAC written by and published by . This book was released on 1987-04 with total page 620 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Government Reports Announcements Index written by and published by . This book was released on 1996-09 with total page 652 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Molecular Dynamics Simulation Studies of Material Modification by Charged Particle Irradiation written by Inkook Jang and published by . This book was released on 2004 with total page 202 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Government Reports Annual Index written by and published by . This book was released on 1991 with total page 1094 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Drag Reduction of Turbulent Flows by Additives written by A. Gyr and published by Springer. This book was released on 2010-10-28 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Drag Reduction of Turbulent Flows by Additives is the first treatment of the subject in book form. The treatment is extremely broad, ranging from physicochemical to hydromechanical aspects. The book shows how fibres, polymer molecules or surfactants at very dilute concentrations can reduce the drag of turbulent flow, leading to energy savings. The dilute solutions are considered in terms of the physical chemistry and rheology, and the properties of turbulent flows are presented in sufficient detail to explain the various interaction mechanisms. Audience: Those active in fundamental research on turbulence and those seeking to apply the effects described. Fluid mechanical engineers, rheologists, those interested in energy saving methods, or in any other application in which the flow rate in turbulent flow should be increased.

Download or read book Molecular Dynamics Investigations of Polymer Solutions Undergoing Shear Flow written by Carsten Aust and published by . This book was released on 2000 with total page 119 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Government Reports Annual Index Corporate author written by and published by . This book was released on 1987 with total page 1028 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1995 with total page 700 pages. Available in PDF, EPUB and Kindle. Book excerpt: Lists citations with abstracts for aerospace related reports obtained from world wide sources and announces documents that have recently been entered into the NASA Scientific and Technical Information Database.

Download or read book Molecular Dynamics of Glass Forming Systems written by George Floudas and published by Springer Science & Business Media. This book was released on 2010-11-25 with total page 183 pages. Available in PDF, EPUB and Kindle. Book excerpt: Pressure is one of the essential thermodynamic variables that, due to some former experimental difficulties, was long known as the “forgotten variable.” But this has changed over the last decade. This book includes the most essential first experiments from the 1960's and reviews the progress made in understanding glass formation with the application of pressure in the last ten years. The systems include amorphous polymers and glass-forming liquids, polypeptides and polymer blends. The thermodynamics of these systems, the relation of the structural relaxation to the chemical specificity, and their present and future potential applications are discussed in detail. The book provides (a) an overview of systems exhibiting glassy behavior in relation to their molecular structure and provides readers with the current state of knowledge on the liquid-to-glass transformation, (b) emphasizes the relation between thermodynamic state and dynamic response and (c) shows that the information on the pressure effects on dynamics can be employed in the design of materials for particular applications. It is meant to serve as an advanced introductory book for scientists and graduate students working or planning to work with dynamics. Several scientific papers dealing with the effects of pressure on dynamics have appeared in leading journals in the fields of physics in the last ten years. The book provides researchers and students new to the field with an overview of the knowledge that has been gained in a coherent and comprehensive way.

Download or read book Effects of Dilute Polymer Additives on the Turbulence Structure Near a Wall written by Hiroaki Yoda and published by . This book was released on 1981 with total page 176 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Molecular Dynamics Method Development and Simulations of Molecule polymer Interactions written by Travis W. Kemper and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: While the second generation REBO potential reproduced reaction enthalpies within reasonable limits, the main deficiency is found to be the short range nature of the potential and the lack of different charge states. However, the computational efficiency allows for a greater sampling of possible reactions, and there for is a good initial evaluation tool to allow for further analysis with more accurate quantum based methods. Next the surface polymerization by ion assisted deposition (SPIAD) process is investigated. The SPIAD process involves the deposition of thermal neutrals and hyperthermal ions to produce oligomer films for use in organic molecule based electronics. In order to study this process thiophene molecules are deposited on thin films of terthiophene. During these simulations the differences in argon and thiophene depositions are examined. In order to investigate the effects of reactivity of the deposited species, argon and atomic oxygen are deposited a set of prototypical polymers. These prototypical polymers, polyethylene, polypropylene and polystyrene, are generated using an amorphous polymer model. Statistical data on probable changes in substrate bonding is presented. Thus, atomic-scale simulations are conducted to advance the plasma and ionbeam treatments of polymer surfaces. Probable modifications are identified using the second generation REBO potential. Sulfur and improved oxygen parameters are developed under the second generation REBO potential formalism. Probable modifications are further analyzed using quantum chemical analysis. To identify the mechanism in which ions modify polymer surfaces.

Download or read book The influence of polymer additives on velocity and temperature fields written by Bernhard GAMPERT and published by . This book was released on 1984 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Structural and Dynamical Properties of Water and Polymers at Surfaces and Interfaces written by Selemon Bekele and published by . This book was released on 2018 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: All-atom molecular dynamics simulations have been carried out to study the wetting of model atactic polystyrene thin films by water droplets as a function of surface polarity, the structure and dynamics at the surface of polymer films, the properties of interfacial water molecules in contact with atactic polystyrene surfaces of varying polarity, and the spreading dynamics of water droplets of varying sizes on a completely wetting surface. The simulated contact angle of a water droplet on atactic polystyrene thin films is found to decrease monotonically with increasing degree of surface oxidation which is used as a measure of surface polarity. The number of hydrogen bonds between water molecules and the polystyrene at the interface is found to monotonically increase with polarity. The contribution of the non-dispersion interactions to the interfacial energy at the polystyrene/water interface has been determined as a function of surface polarity. The roughness of the polystyrene surface and the orientational ordering of the surface phenyl rings are found to be independent of surface polarity when the polystyrene is exposed to vacuum. Surface roughness appears to increase and orientational ordering of surface rings appears to decrease slightly with polarity when the polystyrene is in contact with water. Density profiles of polymer films as a function of distance relative to an instantaneous surface exhibit a structure indicative of a layering at the polymer/vapor interface similar to the typical layered structure observed at the polymer/substrate interface. Interfacial molecules at the polymer/vapor interface have a higher mobility compared to that in the bulk while the mobility of the molecules is lower at the polymer/substrate interface. Time correlation of the instantaneous polymer/vapor interface shows that surface fluctuations are strongly temperature dependent and are directly related to the mobility of polymer chains near the interface. Interfacial water molecules on a bare atactic polystyrene surface and those which do not make hydrogen bonds with the oxidized surfaces are found to have a faster dynamics and appear to have a universal water-water hydrogen bond relaxation time of about 5 ps. Diffusion coefficients and the relaxation times of the water molecules involved in hydrogen bonding with the surface show strong dependence on surface polarity with a hydrophobic to hydrophilic transition regime with contact angle in the range 40-50°. The spreading of water droplets on completely wetting surface is characterized by a bulk part of normal density sliding over a monolayer of high density water. The monolayer has a molecular dimension and moves ahead of the bulk part of the droplet. The monolayer motion exhibits two spreading regimes, each following a power law in time. The bulk part of the droplet initially spreads over the monolayer with increasing radius until a characteristic time t* where the monolayer changes from one power law behavior to another. For times after t* ~ 0.1- 0.5 ns, it shrinks while maintaining what appears to be a constant contact angle until it disappears altogether and only a monolayer of water remains on the substrate.

Download or read book The Influence of Polymer Additives on the Structure of Wall Turbulence written by Elisabetta De Angelis (ingegnere.) and published by . This book was released on 2001 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book An Investigation of Molecular Structure in Drag Reducing Polymer Additives written by W. Michael Reed and published by . This book was released on 1987 with total page 350 pages. Available in PDF, EPUB and Kindle. Book excerpt: Investigates the means by which polymer additives (polyethylene oxide, polyacrylamide) cause drag reduction and concludes that drag reduction is a function of molecular weight, solute concentation and molecular structure of the additive.