Molecular Simulation Of Polymer Solvent Phase Behavior
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Molecular Simulation Of Polymer Solvent Phase Behavior
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Author : John Kennedy Brennan
language : en
Publisher:
Release Date : 1998
Molecular Simulation Of Polymer Solvent Phase Behavior written by John Kennedy Brennan and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1998 with categories.
Thermodynamics And Phase Behavior Or Polymer Blends And Solutions
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Author : Dmitry Gromov
language : en
Publisher:
Release Date : 1997
Thermodynamics And Phase Behavior Or Polymer Blends And Solutions written by Dmitry Gromov and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1997 with categories.
Using Molecular Simulations To Understand Polymer Entanglements And Coacervate Phase Behavior
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Author : Sai Vineeth Bobbili
language : en
Publisher:
Release Date : 2021
Using Molecular Simulations To Understand Polymer Entanglements And Coacervate Phase Behavior written by Sai Vineeth Bobbili and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2021 with categories.
Advancements in computer simulations have led to their application in understanding structure-property relations of polymer melts and solutions. Friction coefficient and entanglement length are two fundamental parameters in modern tube-based theories. In this work, we use molecular dynamics simulations to study the impact of chain architecture and orientation on these two properties. Multiple scaling arguments have been proposed to describe how the entanglement molecular weight depends on polymer architecture and concentration. Such scaling arguments are well supported either by experiments or through simulation data. Each of these arguments makes certain assumptions, which limits their range of validity. Here, we use simulations to explore a wide range of entangled bead-spring ring chains, to find out how entanglement properties vary with chain stiffness and concentration. We quantify entanglement using three techniques: chain shrinking to find the primitive path, measuring the tube diameter by the width of the "cloud" of monomer positions about the primitive path, and directly measuring the plateau modulus. As chain stiffness varies, we observe three distinct scaling regimes, suggestive of the Lin-Noolandi scaling, semiflexible chains, and stiff chains. The packing length p figures prominently in scaling predictions of the entanglement length and bulk modulus for polymer melts and solutions. p has been argued to scale as the ratio of chain displaced volume V and mean square end-to-end distance R^2. This scaling works for several cases; however, it is not obvious how to apply it to chains with side groups, and the scaling must fail for sufficiently thin, stiff chains. In this work, we measure the packing length in simulations, without making any scaling assumptions, as the typical distance of closest approach of two polymer strands in a simulated bead-spring melt using inter-molecular radial distribution functions. While predicting entanglement length has been the focus of several scaling arguments and simulation studies, understanding the behavior of friction coefficient has received less attention. The monomer friction coefficient [zeta] is known to vary with monomer structure, solvent, and concentration; its variation with chain conformation is less well known and appreciated. We explore the decrease of friction coefficient in extensional flow of polymer liquids, during which chains become partially stretched and aligned. In the second half of this dissertation, we use molecular dynamics simulations to investigate the phase behavior of polyelectrolyte complex coacervates. When oppositely charged polyelectrolytes mix in an aqueous solution, associative phase separation gives rise to coacervates. Experiments reveal the phase diagram for such coacervates, and determine the impact of charge density, chain length and added salt. We propose an idealized model and a simple simulation technique to investigate coacervate phase behavior and show the impact of added salt using a phase diagram. Most studies understanding the phase behavior of polyelectrolyte complex coacervates focus on symmetric mixtures of oppositely charged polymers. This is very rare in biological coacervates. Mixing ratio plays an important role in stability of complexes and applications of such coacervates. We use our idealized simulation model to study the impact of charge-asymmetry on the phase behavior of coacervates.
Using Molecular Simulation To Explore Protein And Colloidal Phase Behavior In Bulk Confinement And Mixtures
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Author : Thomas W. Rosch
language : en
Publisher:
Release Date : 2008
Using Molecular Simulation To Explore Protein And Colloidal Phase Behavior In Bulk Confinement And Mixtures written by Thomas W. Rosch and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2008 with categories.
Because of the ubiquity of colloidal solutions in everyday industrial applications such as papermaking and coatings there is a need to be able to efficiently design and manufacture these substances. A related issue concerns the connection between many physiological diseases and heath defects and the stability and phase behavior of certain proteins. It is imperative to understand the physical mechanisms that cause proteins to change their normal solution characteristics. To design colloidal solutions for specific applications as well as to produce preventative medicines and therapies an intimate knowledge of the connection between particle interactions and overall physical properties of the solution is needed. To probe this issue four types of systems are examined. In each system solution conditions are altered affecting the nature and strength of the particle interactions. Our goal is to understand the physics behind the evolution of fluid properties that occurs because of changes in microscopic interactions. The method we employ in this pursuit is grand canonical transition matrix Monte Carlo. We examine an embedded point charge protein model of lysozyme in bulk, mixed with polymer, as well as in confinement. We find that in bulk the model is able to capture qualitatively experimental trends for changes in critical temperature and evolution of the fluid phase diagram with changing solution conditions such as salt concentration and pH. Quantitatively the model predicts a relatively narrow coexistence curve compared to experimental values. It is found that the osmotic second virial coefficient remains relatively constant over a broad range of solutions conditions suggesting a universal magnitude of attraction needed to induce phase separation. We examine a simple system consisting of hard sphere colloids with added Gaussian core polymers. Decreasing the size of the polymers relative to colloids as well as increasing the energetic repulsion between polymers upon overlap results in an overall stabilization of the mixture. Unlike bulk solutions containing molecules of the Carlsson et al. lysozyme model, the osmotic second virial coefficient at the critical point for model colloid-polymer mixtures is not constant but depends on polymer size and interaction. Increasing polymer size or decreasing polymer repulsion results in a larger negative value. Overall the model fails to capture the experimental behavior of polymer excluded volume interactions because its inability to describe the polymers capability of deformation around the colloid. We extend our analysis to a mixture containing the embedded charge model for lysozyme and Gaussian core polymers. Overall, the system exhibited a strong dependence on pH and salt concentration that qualitatively followed experimental trends. Increase of salt concentration or decrease in protein charge decreases the number of polymers needed to induce phase separation. This trend was not sensitive to the size of the polymer relative to the protein. Finally we examine the effect surface interactions have on the phase behavior for the lysozyme model as well as a simple square well model. Both systems exhibited a distinctly non-monotonic variation of its critical temperature as a function of fluid-wall interaction strength. A maximum occurs at an intermediate strength. We introduce two metrics that enable one to predict the location of this maximum. The first is related to the contact angle a fluid makes with the confining substrate while the second is based upon virial coefficient information. Because similar trends are exhibited in both systems we believe that the results should be general in nature.
Multiscale Computational Modeling Of High Pressure Phase Stability Structure And Thermophysical Properties Of Compressible Polyolefin Solutions
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Author : Moeed Shahamat
language : en
Publisher:
Release Date : 2015
Multiscale Computational Modeling Of High Pressure Phase Stability Structure And Thermophysical Properties Of Compressible Polyolefin Solutions written by Moeed Shahamat and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2015 with categories.
"The knowledge of high-pressure phase behavior and phase equilibria of polyethylene (PE) in hydrocarbon solutions is an integral part of the process design and manufacturing of PE via solution polymerization. This thesis focuses on the study of fundamental polymer thermodynamics and key mechanisms that govern phase stability in polyolefin solutions via combined thermodynamics-molecular modeling algorithms.Force field-molecular dynamics simulations are utilized to bridge the gap between experimentally observed macro-scale phase separation phenomena and molecular-level details of fundamental studies of macromolecular thermodynamics in polymer-solvent systems. In this context, the main contributions of the present thesis work focus on molecular thermodynamic characterization of the pressure-induced phase separation (PIPS) mechanism and lower critical solution temperature (LCST) fluid phase behavior of PE solution; high-pressure thermodynamic and structural properties of binary and ternary solutions of PE + hexane and PE + hexane + ethylene, respectively; improvement of the computational efficiency and accuracy of the isobaric-isothermal and canonical ensemble simulations; overcoming the practical challenges involved in the implementation of equation of state theories.A fully-atomistic molecular mechanics force field combined with molecular dynamics is implemented to compute solubility parameter, liquid phase density, structure, and internal pressure of HDPE and hexane over a broad range of pressures. Based upon the knowledge of pressure and temperature dependence of solubility parameters the binary interaction parameter is computed to shed light on phase stability predictions in PIPS mechanism and LCST phase behavior. A molecular-level explanation for the change in cohesive properties and structure of PE and hexane upon raising the external pressure is provided. Additionally, a relation is established between cohesive energy density and internal pressure for the solvent and polymer as a function of pressure. A comparison is reported between electrostatic algorithms of switch function and the particle mesh Ewald method, and also the effect of grid spacing on the computational accuracy of electrostatic energy contribution is revealed.This thesis also implements the state of the art molecular modeling methods and equation of state modeling to report on the pressure dependence of binary PE solution density for various polymer compositions, required to solve the phase equilibria and kinetics of compressible polymer solutions. The effect of the cut-off radius of intermolecular potentials on the non-bonded forces and densities of the polymer-solvent mixture with the objective of improving the computational efficiency of molecular dynamics simulations is investigated and an optimized cut-off distance is suggested for high-pressure molecular mechanics modeling of compressible polyolefin solutions. An atomistic-level analysis of the impact of pressure on the structure of PE-solvent mixture is also provided.The isobaric-isothermal molecular dynamics methodology together with the equation of state model is further extended to incorporate ethylene as unreacted monomer in the solution polymerization process for PE production. The inclusion of supercritical ethylene lays the foundation for the analysis of the effect of adding co-solvent on the density of PE + hydrocarbon solvent system and also to elucidate the impact of pressure and temperature upon the ternary PE solution density. Additionally, a significant insight into the exact nature of intermolecular interactions in the binary subsystems of polymer/solvent/co-solvent is presented. Ultimately, an integrated equation of state-molecular simulation algorithm is presented to compute the characteristic parameters involved in the equation of state theory, which eliminates the need for rigorous experimental phase equilibrium data and tedious non-linear fitting of thermodynamic data." --
Molecular Simulation Of Simple Fluids And Polymers In Nanoconfinement
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Author : Christopher John Rasmussen
language : en
Publisher:
Release Date : 2012
Molecular Simulation Of Simple Fluids And Polymers In Nanoconfinement written by Christopher John Rasmussen and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2012 with Monte Carlo method categories.
Prediction of phase behavior and transport properties of simple fluids and polymers confined to nanoscale pores is important to a wide range of chemical and biochemical engineering processes. A practical approach to investigate nanoscale systems is molecular simulation, specifically Monte Carlo (MC) methods. One of the most challenging problems is the need to calculate chemical potentials in simulated phases. Through the seminal work of Widom, practitioners have a powerful method for calculating chemical potentials. Yet, this method fails for dense and inhomogeneous systems, as well as for complex molecules such as polymers. In this dissertation, the gauge cell MC method, which had previously been successfully applied to confined simple fluids, was employed and extended to investigate nanoscale fluids in several key areas. Firstly, the process of cavitation (the formation and growth of bubbles) during desorption of fluids from nanopores was investigated. The dependence of cavitation pressure on pore size was determined with gauge cell MC calculations of the nucleation barriers correlated with experimental data. Additional computational studies elucidated the role of surface defects and pore connectivity in the formation of cavitation bubbles. Secondly, the gauge cell method was extended to polymers. The method was verified against the literature results and found significantly more efficient. It was used to examine adsorption of polymers in nanopores. These results were applied to model the dynamics of translocation, the act of a polymer threading through a small opening, which is implicated in drug packaging and delivery, and DNA sequencing. Translocation dynamics was studied as diffusion along the free energy landscape. Thirdly, we show how computer simulation of polymer adsorption could shed light on the specifics of polymer chromatography, which is a key tool for the analysis and purification of polymers. The quality of separation depends on the physico-chemical mechanisms of polymer/pore interaction. We considered liquid chromatography at critical conditions, and calculated the dependence of the partition coefficient on chain length. Finally, solvent-gradient chromatography was modeled using a statistical model of polymer adsorption. A model for predicting separation of complex polymers (with functional groups or copolymers) was developed for practical use in chromatographic separations.
Observation Prediction And Simulation Of Phase Transitions In Complex Fluids
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Author : Marc Baus
language : en
Publisher: Springer Science & Business Media
Release Date : 2012-12-06
Observation Prediction And Simulation Of Phase Transitions In Complex Fluids written by Marc Baus and has been published by Springer Science & Business Media this book supported file pdf, txt, epub, kindle and other format this book has been release on 2012-12-06 with Science categories.
Observation, Prediction and Simulation of Phase Transitions in Complex Fluids presents an overview of the phase transitions that occur in a variety of soft-matter systems: colloidal suspensions of spherical or rod-like particles and their mixtures, directed polymers and polymer blends, colloid--polymer mixtures, and liquid-forming mesogens. This modern and fascinating branch of condensed matter physics is presented from three complementary viewpoints. The first section, written by experimentalists, emphasises the observation of basic phenomena (by light scattering, for example). The second section, written by theoreticians, focuses on the necessary theoretical tools (density functional theory, path integrals, free energy expansions). The third section is devoted to the results of modern simulation techniques (Gibbs ensemble, free energy calculations, configurational bias Monte Carlo). The interplay between the disciplines is clearly illustrated. For all those interested in modern research in equilibrium statistical mechanics.
Molecular Dynamic Simulations Of Diffusion And Phase Behaviors Of Colloidal Particles In Two Component Liquid Systems
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Author : Wei Gao
language : en
Publisher:
Release Date : 2017
Molecular Dynamic Simulations Of Diffusion And Phase Behaviors Of Colloidal Particles In Two Component Liquid Systems written by Wei Gao and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2017 with Molecular dynamics categories.
A comprehensive and systematic investigation on the diffusion and phase behaviors of nanoparticles and macromolecules in two component liquid-liquid systems via Molecule Dynamic (MD) simulations is presented in this dissertation. The interface of biphasic liquid systems has attracted great attention because it offers a simple, flexible, and highly reproducible template for the assembly of a variety of nanoscale objects. However, certain important fundamental issues at the interface have not been fully explored, especially when the size of the object is comparable with the liquid molecules. In the first MD simulation system, the diffusion and self-assembly of nanoparticles with different size, shape and surface composition were studied in an oil/water system. It has been found that a highly symmetrical nanoparticle with uniform surface (e.g. buckyball) can lead to a better-defined solvation shell which makes the "effective radius" of the nanoparticle larger than its own radius, and thus, lead to slower transport (diffusion) of the nanoparticles across the oil-water interface. Poly(N-isopropylacrylamide) (PNIPAM) is a thermoresponsive polymer with a Lower Critical Solution Temperature (LCST) of 32°C in pure water. It is one of the most widely studied stimulus-responsive polymers which can be fabricated into various forms of smart materials. However, current understanding about the diffusive and phase behaviors of PNIPAM in ionic liquids/water system is very limited. Therefore, two biphasic water-ionic liquids (ILs) systems were created to investigate the interfacial behavior of PNIPAM in such unique liquid-liquid interface. It was found the phase preference of PNIPAM below/above its LCST is dependent on the nature of ionic liquids. This potentially allows us to manipulate the interfacial behavior of macromolecules by tuning the properties of ionic liquids and minimizing the need for expensive polymer functionalization. In addition, to seek a more comprehensive understanding of the effects of ionic liquids on the phase behavior of PNIPAM, PNIPAM was studied in two miscible ionic liquids/water systems. The thermodynamic origin causes the reduction of LCST of PNIPAM in imidazolium based ionic liquids/water system was found. Energy analysis, hydrogen boding calculation and detailed structural quantification were presented in this study to support the conclusions.
Modeling And Simulation In Polymers
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Author : Purushottam D. Gujrati
language : en
Publisher: John Wiley & Sons
Release Date : 2010-03-30
Modeling And Simulation In Polymers written by Purushottam D. Gujrati and has been published by John Wiley & Sons this book supported file pdf, txt, epub, kindle and other format this book has been release on 2010-03-30 with Technology & Engineering categories.
Filling a gap in the literature and all set to become the standard in this field, this monograph begins with a look at computational viscoelastic fluid mechanics and studies of turbulent flows of dilute polymer solutions. It then goes on discuss simulations of nanocomposites, polymerization kinetics, computational approaches for polymers and modeling polyelectrolytes. Further sections deal with tire optimization, irreversible phenomena in polymers, the hydrodynamics of artificial and bacterial flagella as well as modeling and simulation in liquid crystals. The result is invaluable reading for polymer and theoretical chemists, chemists in industry, materials scientists and plastics technologists.
Phase Behavior Of Polymer Blends
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Author : Karl Freed
language : en
Publisher: Springer Science & Business Media
Release Date : 2005-09-01
Phase Behavior Of Polymer Blends written by Karl Freed and has been published by Springer Science & Business Media this book supported file pdf, txt, epub, kindle and other format this book has been release on 2005-09-01 with Technology & Engineering categories.