Download or read book Reactions and Interfacial Behaviors of the Water Amorphous Silica System from Classical and Ab Initio Molecular Dynamics Simulations written by Jessica M. Rimsza and published by . This book was released on 2016 with total page 214 pages. Available in PDF, EPUB and Kindle. Book excerpt: Due to the wide application of silica based systems ranging from microelectronics to nuclear waste disposal, detailed knowledge of water-silica interactions plays an important role in understanding fundamental processes, such as glass corrosion and the long term reliability of devices. In this dissertation, atomistic computer simulation methods have been used to explore and identify the mechanisms of water-silica reactions and the detailed processes that control the properties of the water-silica interfaces due to their ability to provide atomic level details of the structure and reaction pathways. The main challenges of the amorphous nature of the silica based systems and nano-porosity of the structures were overcome by a combination of simulation methodologies based on classical molecular dynamics (MD) simulations with Reactive Force Field (ReaxFF) and density functional theory (DFT) based ab initio MD simulations. Through the development of nanoporous amorphous silica structure models, the interactions between water and the complex unhydroxylated internal surfaces identified the unusual stability of strained siloxane bonds in high energy ring structure defects, as well as the hydroxylation reaction kinetics, which suggests the difficulty in using DFT methods to simulate Si-O bond breakage with reasonable efficiency. Another important problem addressed is the development of silica gel structures and their interfaces, which is considered to control the long term residual dissolution rate in borosilicate glasses. Through application of the ReaxFF classical MD potential, silica gel structures which mimic the development of interfacial layers during silica dissolution were created A structural model, consisting of dense silica, silica gel, and bulk water, and the related interfaces was generated, to represent the dissolution gel structure. High temperature evolution of the silica-gel-water (SGW) structure was performed through classical MD simulation of the system, and growth of the gel into the water region occurred, as well as the formation of intermediate range structural features of dense silica. Additionally, hydroxylated silica monomers (SiO4H4) and longer polymerized silica chains were formed in the water region, indicating that glass dissolution is occurring, even at short time frames. The creation of the SGW model provides a framework for a method of identifying how interfacial structures which develop at glass-water interfaces can be incorporated into atomistic models for additional analysis of the dissolution of silicates in water.
Download or read book Surface and Interface Science Volumes 7 and 8 written by Klaus Wandelt and published by John Wiley & Sons. This book was released on 2020-03-30 with total page 1002 pages. Available in PDF, EPUB and Kindle. Book excerpt: In ten volumes, this unique handbook covers all fundamental aspects of surface and interface science and offers a comprehensive overview of this research area for scientists working in the field, as well as an introduction for newcomers. Volume 1: Concepts and Methods Volume 2: Properties of Elemental Surfaces Volume 3: Properties of Composite Surfaces: Alloys, Compounds, Semiconductors Volume 4: Solid-Solid Interfaces and Thin Films Volume 5: Solid-Gas Interfaces I Volume 6: Solid-Gas Interfaces II Volume 7: Liquid and Biological Interfaces Volume 8: Interfacial Electrochemistry Volume 9: Applications of Surface Science I Volume 10: Applications of Surface Science II Content of Volumes 7 & 8: * Probing Liquid/Solid Interfaces at the Molecular Level * Structure and Dynamics of Liquid-Solid Interfaces * Adsorption of Biomolecules * Liquid Surfaces * Surfaces of Ionic Liquids * Superhydrophobicity * Cell Penetrating Peptides Targeting and Distorting Biological Membranes * Theory of Solid/Electrolyte Interfaces * Metal/Electrolyte Interfaces: An Atomic View * X-Ray Spectroscopy at Electro-Catalytic Interfaces * Fundamental Aspects of Electro-Catalysis * Non-Linear Processes at Solid/Liquid Interfaces
Download or read book Structure and Dynamics of Molecules at Water silica and Water carbon Dioxide Interfaces written by Hui Zhang and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: The interface between silica and water is one of the most technologically relevant surfaces. An especially important aspect of this system is its inherent negative charges at most pH values, and the resulting electrokinetic phenomena that take place in the fluid region. We have constructed a realistic model for the charged silica/water interface where many of these standard models can be tested. The model allows for undissociated and dissociated silanol groups. We have also conducted ab initio MD simulations of a smaller system consisting of a hydrated silica slab. The comparison of the radial distribution functions from the ab initio MD simulations and those obtained from the empirical model are favorable. The hydrophobic and hydrophilic nature of silanol-poor and silanol-rich regions of the amorphous silica surface observed in our empirical model is reproduced in the ab initio MD simulations of the smaller slab. In the initial stages of our ab initio MD simulations, we observe various chemical processes that represent different hydroxylation mechanisms of the surface. To explain why dynamical properties of an aqueous electrolyte near a charged surface seem to be governed by a surface charge less than the actual one, the canonical Stern model supposes an interfacial layer of ions and immobile fluid. However, large ion mobilities within the Stern layer are needed to reconcile the Stern model with surface conduction measurements. Modeling the aqueous electrolyte/amorphous silica interface at typical charge densities, a prototypical double layer system, the flow velocity does not vanish until right at the surface. The Stern model is a good effective model away from the surface, but cannot be taken literally near the surface. Indeed, simulations show no ion mobility where water is immobile, nor is such mobility necessary since the surface conductivity in the simulations is comparable to experimental values. Our studies suggest a richer, microscopic picture that allows for much greater mobility near the surface without a sharp boundary between mobile fluid and immobile ion layer, but still accounts for observed phenomena. The effect of salt concentration, surface charge density (which would be controlled experimentally by varying the pH) and local water viscosity on electrokinetic phenomena is explored. The structural properties of the interface between water and carbon dioxide are very important in many areas of chemistry and physics, such as supercritical extraction, electrochemistry and ion transport across membranes. In my study, the structural properties of the interface of water and CO2 are investigated by means of molecular dynamics (MD) simulations. The capillary wave theory is used to find the interface positions and the shape of the interface is determined by this theory. The density profiles of CO2 and water are extracted based on capillary wave theory. The density profiles are very helpful to calculate the surface excess and check whether there is a wetting transition when the pressure is increased. Molecular orientations of water and CO2 are calculated to give detailed information of the interface structure. Both water and CO2 molecules near the interface prefer to laying parallel with respect to the surface. The preferred orientational distribution of molecules near the surface gives rise to the surface potential which is calculated to better understand the electrodynamics of the interface.
Download or read book Structural Configuration of Amorphous Silica Surface with Different Terminating Groups Using Classical and Ab Initio Molecular Dynamics written by Md Azharul Islam and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The surface interaction properties of amorphous silica are crucial various sectors of technology, yet many aspects of these interactions are still not fully understood because amorphous silica's nature is non-periodic. In this study, computational simulations are used to understand the bonding mechanism and atomic structure of the amorphous silica surfaces with different passivating groups. Amorphous silica surfaces are generated by melt-quench dynamics using classical molecular dynamics (MD). Then, subdomains of these surfaces containing an undercoordinated surface atom are selected for ab initio density functional theory calculations. Relaxed surface geometries including hydroxyl, methyl, and fluoromethyl passivating groups are determined from density functional theory (DFT)-based structural relaxation calculations, along with Born-Oppenheimer MD at 300 K to determine the bond dissociation energy, bond length, and angle. This study provides a deeper understanding of the interactions between silica surfaces and this information can be used to improve the production and processing of silica-based materials.
Download or read book Handbook of Adhesion Technology written by Lucas F. M. da Silva and published by Springer Science & Business Media. This book was released on 2011-06-10 with total page 1569 pages. Available in PDF, EPUB and Kindle. Book excerpt: Adhesives have been used for thousands of years, but until 100 years ago, the vast majority was from natural products such as bones, skins, fish, milk, and plants. Since about 1900, adhesives based on synthetic polymers have been introduced, and today, there are many industrial uses of adhesives and sealants. It is difficult to imagine a product—in the home, in industry, in transportation, or anywhere else for that matter—that does not use adhesives or sealants in some manner. The Handbook of Adhesion Technology is intended to be the definitive reference in the field of adhesion. Essential information is provided for all those concerned with the adhesion phenomenon. Adhesion is a phenomenon of interest in diverse scientific disciplines and of importance in a wide range of technologies. Therefore, this handbook includes the background science (physics, chemistry and materials science), engineering aspects of adhesion and industry specific applications. It is arranged in a user-friendly format with ten main sections: theory of adhesion, surface treatments, adhesive and sealant materials, testing of adhesive properties, joint design, durability, manufacture, quality control, applications and emerging areas. Each section contains about five chapters written by internationally renowned authors who are authorities in their fields. This book is intended to be a reference for people needing a quick, but authoritative, description of topics in the field of adhesion and the practical use of adhesives and sealants. Scientists and engineers of many different backgrounds who need to have an understanding of various aspects of adhesion technology will find it highly valuable. These will include those working in research or design, as well as others involved with marketing services. Graduate students in materials, processes and manufacturing will also want to consult it.
Download or read book Computational Modeling of Inorganic Nanomaterials written by Stefan T. Bromley and published by CRC Press. This book was released on 2016-04-06 with total page 429 pages. Available in PDF, EPUB and Kindle. Book excerpt: Computational Modeling of Inorganic Nanomaterials provides an accessible, unified introduction to a variety of methods for modeling inorganic materials as their dimensions approach the nanoscale. With contributions from a team of international experts, the book guides readers on choosing the most appropriate models and methods for studying the stru
Download or read book The Water amorphous Silica Interface written by Yun Kyung Shin and published by . This book was released on 2011 with total page 137 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: Advances in the construction of nanoscale biomedical devices requires increasingly realistic descriptions of interactions with biomolecules, and with fluid flow within micro- and nanochannels. We have made progress in both areas for nanostructures fabricated from amorphous silica. Silica is a material commonly used to fabricate biomedical devices, and the interactions of silica with aqueous solutions and biomolecules are of great importance in many fields. We developed a tractable model for biomolecules at the water/amorphous silica interface. This interaction model is based on one previously developed for the amorphous silica/water interface. Quantum chemical calculations of a series of probe molecules that mimic the common functional groups found in biomolecules were performed near a characteristic silica fragment. Our interaction model was designed to best reproduce the quantum chemical results. Then we investigated binding of two tripeptides (lys-trp-lys and glu-trp-glu) at the amorphous silica/water interface using molecular dynamics simulations. The preliminary studies reveal the great variety of binding motifs possible when biomolecules interact with silica, and illustrate how a peptide with overall negative charge like glu-trp-glu might bind to silica by hydrophilic/hydrophobic interactions on the highly inhomogeneous silica surface.
Download or read book Classical Molecular Dynamics and AB initio Simulations of Chemical mechanical Polishing of Amorphous Silica written by Evgueni A. Chagarov and published by . This book was released on 2003 with total page 408 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Structures and Dynamics of Interfacial Water written by Fujie Tang and published by Springer. This book was released on 2019-06-20 with total page 93 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book focuses on the study of the interfacial water using molecular dynamics simulation and experimental sum frequency generation spectroscopy. It proposes a new definition of the free O-H groups at water-air interface and presents research on the structure and dynamics of these groups. Furthermore, it discusses the exponential decay nature of the orientation distribution of the free O-H groups of interfacial water and ascribes the origin of the down pointing free O-H groups to the presence of capillary waves on the surface. It also describes how, based on this new definition, a maximum surface H-bond density of around 200 K at ice surface was found, as the maximum results from two competing effects. Lastly, the book discusses the absorption of water molecules at the water–TiO2 interface. Providing insights into the combination of molecular dynamics simulation and experimental sum frequency generation spectroscopy, it is a valuable resource for researchers in the field.
Download or read book Probing the Chemistry Structure and Dynamics of the Water silica Interface written by Glenn K. Lockwood and published by . This book was released on 2013 with total page 197 pages. Available in PDF, EPUB and Kindle. Book excerpt: Despite its natural abundance and wide-ranging technological relevance, much remains unknown or unclear about water-silica interfaces. Computer simulation stands to bridge the gaps of knowledge left by experiment, and a recently developed Dissociative Water Potential has enabled the simulation of large amorphous silica surfaces in contact with water without having to impose a model of surface chemistry a priori. Earlier work with this model has revealed the existence of several protonated surface sites such as SiOH2+ and Si-(OH+)-Si that have yet to be extensively characterized. However, both experiment and quantum mechanical simulation have provided an increasing body of evidence that suggests these sites exist, and these sites may play key roles in some of the unexplained phenomena observed in water-silica systems. To this end, this Dissociative Water Potential has been applied to develop a comprehensive picture of the chemistry, structure, and dynamics of the water-silica interface that is unbiased by any expectation of what sites should form. The bridging OH site, Si-(OH+)-Si, does form and is characterized as a highly acidic site that occurs predominantly on strained Si-O-Si bridges near the interface. Similarly, the transient formation of SiOH2+ is observed, and this site is found to be more acidic than Si-(OH+)-Si. In addition to H3O+ that forms near the interface, all of these sites readily deprotonate and are expected to play a role in the enhanced proton conductivity experimentally observed in hydrated mesoporous silica. The reactions between water and silica are particularly relevant to the engineering of nuclear waste forms, and the role of water-silica interactions are also explored within the context of the degradation of silica-based waste forms exposed to radiation. Despite the significant simulation effort employed in glassy waste form research, no molecular models of radiation damage in silica include the effects of moisture. This deficiency is addressed, and water is found to play a significant role in accelerating the degradation of amorphous silica under irradiation. Water inhibits healing of the network and promotes the formation of voids into which more water can penetrate, giving way to new damage accumulation mechanisms not seen in any past simulations.
Download or read book Ab Initio Molecular Dynamics written by Dominik Marx and published by Cambridge University Press. This book was released on 2009-04-30 with total page 503 pages. Available in PDF, EPUB and Kindle. Book excerpt: Ab initio molecular dynamics revolutionized the field of realistic computer simulation of complex molecular systems and processes, including chemical reactions, by unifying molecular dynamics and electronic structure theory. This book provides the first coherent presentation of this rapidly growing field, covering a vast range of methods and their applications, from basic theory to advanced methods. This fascinating text for graduate students and researchers contains systematic derivations of various ab initio molecular dynamics techniques to enable readers to understand and assess the merits and drawbacks of commonly used methods. It also discusses the special features of the widely used Car–Parrinello approach, correcting various misconceptions currently found in research literature. The book contains pseudo-code and program layout for typical plane wave electronic structure codes, allowing newcomers to the field to understand commonly used program packages and enabling developers to improve and add new features in their code.
Download or read book Journal of the Chemical Society written by and published by . This book was released on 1991 with total page 562 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Effects of Water on Chemomechanical Instabilities in Amorphous Silica written by Emílio César Cavalcante Melo da Silva and published by . This book was released on 2007 with total page 228 pages. Available in PDF, EPUB and Kindle. Book excerpt: (Cont.) We found that water reduces the tensile strength by both reducing the athermal failure strain and the energy barrier for failure. In summary, we demonstrate experimentally that the tensile strength of amorphous silica is governed by the nanoscale crack initiation event, after which the system fails in a brittle manner. Using a multiscale approach, we describe the nanoscale mechanism through MD simulation and the effect of water through MO simulation, bridging the gap between breaking a single bond and breaking a macroscopic body in tension.
Download or read book Summary Record of the 1162nd Meeting Chamber B Held at the Palais Wilson Geneva on Tuesday 12 September 2006 written by and published by . This book was released on 2006 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Molecular Dynamics Simulation Study of Thermal Resistance Between Amorphous Silica Nanoparticles Under Vacuum and in the Presence of Water Vapor written by Fanhe Meng and published by . This book was released on 2018 with total page 141 pages. Available in PDF, EPUB and Kindle. Book excerpt: Nanoparticle-based materials are of interest because of their unique thermal properties. Possessing the lowest thermal conductivities of any solid materials known, they have been widely used as insulating materials in a variety of macroscale and microscale applications.
Download or read book Understanding Structure Thermodynamics and Dynamics of Silica Liquids and Glasses Using Atomistic Simulations and Machine Learning written by Zheng Yu and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Glass materials are found all around us, but fundamental questions about the nature of their amorphous structures and formation processes remain unsolved after decades of research. In this dissertation, silica, an archetype glass former, is taken as an example glass for investigations into glass structures, thermodynamics, dynamics, two-level systems (TLS), and atomic interactions based on molecular dynamics simulations and machine learning methods. Specifically, we investigate the structure-thermodynamic stability relationship using a library of silica inherent structures generated from melt-quench and replica exchange molecular dynamics simulations. Based on machine learning, we find that short-range and medium-range features play very different roles on the glass stability across the liquid and glass regions. We then revisit an interesting dynamical transition in silica liquid, the fragile-to-strong transition (FTS), from the perspective of microscopic dynamics. By machine learning to classify atomic rearrangements, the FTS is found to originate from the two types of energy barriers in silica, representing a fast and a slow microscopic dynamics channel. The fast channel controlled by the short-range defects closes rapidly with decreasing temperature, causing the fragility crossover. A similar approach is also applied to investigate TLS. We predict TLS densities in a large number of inherent structures with a variety of glass stability using machine learning and verify them using molecular dynamics simulations. We find a decrease in the TLS density with the fictive temperature, which can be described by a quadratic function as suggested by the random first-order transition theory. Lastly, we introduce a linear machine learning force matching approach that can directly extract pair atomic interactions from ab initio calculations in amorphous materials. This approach is applied to silica to understand the atomic interactions within its structure and develop a new classical force field. Through the comprehensive fundamental investigations on the nature of silica glass and liquid, I hope the understandings and methods presented in this dissertation can be transferred to study other glass-forming systems.
Download or read book The Kinetics of Silica water Reactions written by James Donald Rimstidt and published by . This book was released on 1981 with total page 160 pages. Available in PDF, EPUB and Kindle. Book excerpt:
