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Author: Selemon Bekele
Publisher:
ISBN:
Category : Molecular dynamics
Languages : en
Pages : 0
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Book Description
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.
Author: Selemon Bekele
Publisher:
ISBN:
Category : Molecular dynamics
Languages : en
Pages : 0
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Book Description
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.
Author: H. Jellinek
Publisher: Springer Science & Business Media
ISBN: 146158681X
Category : Technology & Engineering
Languages : en
Pages : 191
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Book Description
This symposium was held at the l6lst ACS National Meeting, Los Angeles, March/April 1971. It represents a contribution to the discussion of problems connected with the state of water near macromolecules. Some papers are only peripheral to the problem of water structure but may become quite pertinent in specific cases. Questions concerned with water structure, rate of hydration, and similar problems are of importance for biological processes and are still not yet well understood. It is hoped that the papers presented here will be of some help in the clarification of problems in this area. H. H. G. Jellinek Department of Chemistry Clarkson College of Technology Potsdam, New York September, 1971 v CONTRIBUTORS S. Ablett, Unilever Research Laboratory, Colworth House, Sharnbrook, Bedford, England M. Anbar, Stanford Research Institute, Menlo Park, California F. W. Cope, Biochemistry Division, Aerospace Medical Research Laboratory, U. S. Naval Air Development Center, Warminster, Pennsylvania B. Crist, Camille Dreyfus Laboratory, Research Triangle Park, North Carolina F. Franks, Unilever Research Laboratory, Colworth House, Sharnbrook, Bedford, England H. R, Gloria, NASA-Ames Research Center, Moffett Field, California G. W. Gross, New Mexico Institute of Mining and Technology, Socorro, New Mexico H. R. Hansen, The Procter & Gamble Company, Miami Valley Laboratories, Cincinnati, Ohio R. S. Kaiser, Research Laboratories, Eastman Kodak Company, Rochester, New York N. Laiken, Department of Chemistry, The University of Oregon, Eugene, Oregon C. E. Lamaze, Camille Dreyfus Laboratory, Research Triangle Park, North Carolina G. N.
Author: Yeneneh Yalew Yimer
Publisher:
ISBN:
Category : Monomolecular films
Languages : en
Pages : 168
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Book Description
Polymer-based solar cells (PSCs) require significant improvements in efficiency and life time in order to be commercially viable. Interfacial structure and morphology dictate the performance of PSCs, and these properties in turn depend on processing conditions and surface chemistry. To optimize device performance, detailed knowledge of the factors most critical to the molecular-level structure, morphology and dynamics of donor/acceptor systems at interfaces will be necessary. For one promising donor, poly(3-hexylthiophene (P3HT), we have utilized all-atom and coarse-grained molecular dynamics simulations to investigate such properties at liquid/vacuum, solid/liquid and solid/solid interfaces. At liquid/vacuum interfaces, static and dynamic properties of P3HT films and their dependence on temperature and molecular weight were studied. P3HT chains showed ordering through preferential exposure of side-chain at the interface, and surface tension showed strong dependence on temperature and molecular weight. Properties such as self-diffusion coefficients, chain end-to-end distance and torsion autocorrelations were also utilized to quantify the dynamics of the P3HT chains in the film. Both static and dynamic properties of P3HT were found to be in agreement with well-known models for polymers.Subsequent simulations of P3HT/water systems offered insight into the wetting behavior of P3HT and the nature of the solid-liquid interface in crystalline and amorphous P3HT. From contact angle calculations, different P3HT surfaces were determined to be hydrophobic. In the time scale of our simulations, no observable change in the orientation of the P3HT at interfaces was observed.Furthermore, the molecular ordering of P3HT close to substrates is expected to be the key to device performance. Ordering of P3HT chains at the interface can be tuned by altering the substrate surface chemistry. We investigated the effect of surface chemistry on the ordering of P3HT on self-assembled monolayers (SAMs) of n-alkanethiols. The results showed that the ordering of P3HT strongly depends on the P3HT-SAM interactions. The effect of solvent on the P3HT-SAM interactions was also studied. In addition, we characterized the surface properties of pure SAMs on gold 111. The end-functionalized network structure was found to be correlated to the adsorption sites. For P3HT/acceptor systems, all-atom simulations are challenging because of the need to access large spatial and temporal regimes. To overcome this, we developed a coarse-grained model for P3HT based on the all-atom force field. The coarse-grained model showed good agreement with bulk and interfacial properties obtained from the all-atom model and has a great potential for analyzing morphology and dynamics of P3HT/acceptor blends.
Author: Samuel Safran
Publisher: CRC Press
ISBN: 0429965680
Category : Science
Languages : en
Pages : 285
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Book Description
Understanding the structural and thermodynamic properties of surfaces, interfaces, and membranes is important for both fundamental and practical reasons. Important applications include coatings, dispersants, encapsulating agents, and biological materials. Soft materials, important in the development of new materials and the basis of many biological systems, cannot be designed using trial and error methods due to the multiplicity of components and parameters. While these systems can sometimes be analyzed in terms of microscopic mixtures, it is often conceptually simpler to regard them as dispersions and to focus on the properties of the internal interfaces found in these systems. The basic physics centers on the properties of quasi-two-dimensional systems embedded in the three-dimensional world, thus exhibiting phenomena that do not exist in bulk materials. This approach is the basis behind the theoretical presentation of Statistical Thermodynamics of Surfaces, Interfaces, and Membranes. The approach adapted allows one to treat the rich diversity of phenomena investigated in the field of soft matter physics (including both colloid/interface science as well as the materials and macromolecular aspects of biological physics) such as interfacial tension, the roughening transition, wetting, interactions between surfaces, membrane elasticity, and self-assembly. Presented as a set of lecture notes, this book is aimed at physicists, physical chemists, biological physicists, chemical engineers, and materials scientists who are interested in the statistical mechanics that underlie the macroscopic, thermodynamic properties of surfaces, interfaces, and membranes. This paperback edition contains all the material published in the original hard-cover edition as well as additional clarifications and explanations.
Author: American Chemical Society. Rocky Mountain Regional Meeting
Publisher: Springer
ISBN:
Category : Science
Languages : en
Pages : 200
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Book Description
A small symposium on The Dynamic Aspects of Polymer Surfaces was held as part of the Rocky Mountain Regional American Chemical Society meeting, June, 1986, in Denver, Colorado. In view of the growing activity and interest in polymer surface dynamics, the participants agreed to publish their papers under the auspices of Plenum Press. The authors and participants join me in wishing that this volume will be of assistance to those studying and applying polymeric materials and that it will contribute to the growing awareness that polymer surfaces are indeed dynamic and undergo time- and temperature-dependent relaxations in response to changes in their local environment. J. D. Andrade Salt Lake City, Utah January 1987 CONTENTS Polymer Surface and Interface Dynamics: An Introduction ••••••••••••••• l J. D. Andrade Modeling of the Wilhelmy Contact Angle Method with Practical Sample Geometr i es •••••••••••••••••••••••••••••••••••••••••••••••• 9 P. Dryden, J. H. Lee, J. M. Park, and J. D. Andrade Contact Angles at Polymer~ater Interface; Temperature Dependence and Induced Deformation ••••••••••••••••••••••••. ••••• 25 M. S. Jhon and S. H. Yuk Orientation Phenomena at Polymer-Water Interfaces ••••••••••••••••••••• 45 L. Lavielle Dynamic Contact Angle Studies of N-Alkyl Derivatized Boro-Silicate Glass Surfaces •••••••••••••••••••••••••••••••••••• 67 J. M. Park and J. D. Andrade Surface Mobility and Structural Transitions of Poly(n-Alkyl Methacrylates) Probed by Dynamic Contact Angle Measurement •••••• 89 H. S. van Damme, A. H. Hogt, and J. Feijen Dynamic Wettability of Hydrophobic Polymers •••••••••••••••••••••••••• lOl M. J. OWen, T. M. Gentle, T. Orbeck, and D. E.
Author: Hari Singh Nalwa
Publisher: Elsevier
ISBN: 0080533825
Category : Technology & Engineering
Languages : en
Pages : 1915
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Book Description
This handbook brings together, under a single cover, all aspects of the chemistry, physics, and engineering of surfaces and interfaces of materials currently studied in academic and industrial research. It covers different experimental and theoretical aspects of surfaces and interfaces, their physical properties, and spectroscopic techniques that have been applied to a wide class of inorganic, organic, polymer, and biological materials. The diversified technological areas of surface science reflect the explosion of scientific information on surfaces and interfaces of materials and their spectroscopic characterization. The large volume of experimental data on chemistry, physics, and engineering aspects of materials surfaces and interfaces remains scattered in so many different periodicals, therefore this handbook compilation is needed.The information presented in this multivolume reference draws on two decades of pioneering research on the surfaces and interfaces of materials to offer a complete perspective on the topic. These five volumes-Surface and Interface Phenomena; Surface Characterization and Properties; Nanostructures, Micelles, and Colloids; Thin Films and Layers; Biointerfaces and Applications-provide multidisciplinary review chapters and summarize the current status of the field covering important scientific and technological developments made over past decades in surfaces and interfaces of materials and spectroscopic techniques with contributions from internationally recognized experts from all over the world. Fully cross-referenced, this book has clear, precise, and wide appeal as an essential reference source long due for the scientific community. The complete reference on the topic of surfaces and interfaces of materialsThe information presented in this multivolume reference draws on two decades of pioneering researchProvides multidisciplinary review chapters and summarizes the current status of the fieldCovers important scientific and technological developments made over past decades in surfaces and interfaces of materials and spectroscopic techniquesContributions from internationally recognized experts from all over the world
Author: K. Raghavan
Publisher:
ISBN:
Category :
Languages : en
Pages : 38
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Book Description
An analytical form of the interaction potential between rigid water-rigid metal surface, which takes into account the surface symmetry and its corrugation is developed. Using this potential the structure and dynamics of water at Pt (111) interface is investigated. At 300K the adjacent to the metal surface water layer displays solid-like properties. The next two layers of water display ordering similar to ice-I. Beyond these three layers the structure and dynamics of water is bulk like. Keywords: Molecular dynamics, Computer simulation, Water-metal interface.
Author: Denis Le Bihan
Publisher: Pan Stanford Publishing
ISBN: 981430316X
Category : Medical
Languages : en
Pages : 380
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Book Description
The main objective of this book is to bring together multidisciplinary contributions from leading authorities on the properties and roles of water in cell systems which are otherwise dispersed in the literature and difficult to gather. The authors are drawn from areas of physics, chemistry, biology and physiology, where water plays a central role. The book focuses on current research and developments in the theoretical and experimental studies of water in biological systems and compounds, such as interaction with hydrophobic or hydrophilic structures, protein and membrane surfaces. It provides insights into the importance of water in cellular processes and physiology and, ultimately, in life, brain function, and health.
Author: Hari Singh Nalwa
Publisher:
ISBN:
Category : Interfaces (Physical sciences)
Languages : en
Pages : 622
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Book Description
Author: Richard Catlow
Publisher: Springer Science & Business Media
ISBN: 9400924844
Category : Science
Languages : en
Pages : 543
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Book Description
Computer Modelling techniques have developed very rapidly during the last decade, and interact with many contemporary scientific disciplines. One of the areas of greatest activity has concerned the modelling of condensed phases, including liquids solids and amorphous systems, where simulations have been used to provide insight into basic physical processes and in more recent years to make reliable predictions of the properties of the systems simulated. Indeed the predictive role of simulations is increasingly recognised both in academic and industrial contexts. Current active areas of application include topics as diverse as the viscosity of liquids, the conformation of proteins, the behaviour of hydrogen in metals, the diffusion of molecules in porous catalysts and the properties of micelles. This book, which is based on a NATO ASI held at the University of Bath, UK, from September 5th-17th, 1988, aims to give a general survey of this field, with detailed discussions both of methodologies and of applications. The earlier chapters of the book are devoted mainly to techniques and the later ones to recent simulation studies of fluids, polymers (including biological molecules) and solids. Special attention is paid to the role of interatomic potentials which are the fundamental physical input to simulations. In addition, developments in computer hardware are considered in depth, owing to the crucial role which such developments are playing in the expansion of the horizons of computer modelling studies.
