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Experimental Studies of Solvent Quality in Model Polymeric Fluids PDF

Author: Michael James Solomon
Publisher:
ISBN:
Category :
Languages : en
Pages : 370

Book Description

Author: Shikha Somani
Publisher: Stanford University
ISBN:
Category :
Languages : en
Pages : 135

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Book Description
Polymers undergo a sharp coil to stretch conformational transition in extension dominated flows when the strain rate exceeds a critical value. Dramatic change in flow behavior is known to occur at the coil-stretch transition, making it useful for several commercial applications. Despite decades of study, this phenomenon remains surrounded with controversy as the effect of solvent properties and fluid flow elements on this transition is not fully understood. In this work, we present a study of the coil-stretch transition and related hysteresis phenomenon using stochastic computer simulations. We first investigate the effect of solvent quality on the coil-stretch transition using Brownian dynamics simulations. Unlike experiments, which are plagued with problems related to polydispersity of polymers and inaccurate control over flow profiles, simulations offer a powerful platform to systematically study the effect of solvent quality while keeping all other parameters in the system constant. The system consists of a polymer subjected to planar elongational flow in both theta solvents and good solvents. The polymer is represented by a bead-spring chain model undergoing elongational flow. Solvent-mediated effects such as fluctuating hydrodynamic interactions (HI) and excluded volume (EV) are included rigorously. Conformational hysteresis is understood in terms of a 1-D energy landscape theory with an activation energy barrier for transition. At steady state, depending upon the flow rate, the energy landscape can either have one or two energy wells. An energy landscape with one well corresponds to the coiled state at low flow rate and stretched state at high flowrate. The double welled landscape corresponds to the hysteretic regime where both coiled and stretched conformational states coexist across the ensemble population. A key factor in determining the effect of solvent quality is the use of a proper measure of solvent quality. In almost all earlier studies, the effect of molecular weight on solvent quality has been neglected, producing inconsistent results. Here, the solvent quality is quantified carefully such that the effect of molecular weight and temperature is taken into account. Contrary to earlier findings, it is observed that with improvement in solvent quality, the chains unravel faster and the critical strain rate at which the coil to stretch transition takes place decreases. Furthermore, the solvent quality has a profound effect on the scaling of the critical strain rate with molecular weight and on both the transient and steady state properties of the system. Universal functions are shown to exist for the observed dynamic and static properties, which will prove useful in determining the operating parameters for experiments. In particular, the ratio of the two different relaxation times (longest relaxation time and zero shear rate viscosity) is found to be a universal function of solvent quality independent of molecular weight. The relaxation times (both the longest relaxation time and the zero shear rate viscosity) increase while the critical strain rate is found to decrease with solvent quality. Next, the study of conformational hysteresis is extended to more complicated 3-D flows to understand the effect of flow vorticity on this phenomenon. Heretofore, there has been no systematic methodology for studying the dynamical interactions between polymer molecules and elementary flow patterns in three-dimensional flows. Such a framework is essential not just for gaining valuable insights into the physics of complex fluids at a fundamental level, but it is also crucial for various important applications like turbulent drag reduction where the underlying physical mechanisms involve dynamical interactions between polymers and turbulence fine scale flow features. Such a study is presented here to provide a framework to interpret complex fluid phenomenon in terms of elementary flow patterns. We investigate the conformational hysteresis using rigorous Brownian dynamics simulations and specifically explore the effect of flow vorticity on the lifetime and width of the hysteresis window in 3-D flows. A systematic procedure is developed with careful eigenvalue analysis to explore the sole effect of vorticity on polymer dynamics keeping the principal strain rate fixed. It is observed that the hysteresis width shrinks due to increase in flow vorticity irrespective of the flow type (bi-extensional, bi-compressional, spiral-inwards, spiral-outwards etc). This is further traced to the alignment of eigenvectors with the principal eigenvector direction leading to enhanced fluctuations. Vorticity is found to have a significant effect on both the transient and the steady state properties. Understanding the effect of vorticity on polymer conformational hysteresis can further help in understanding the fundamental processes in complex flows.

Author: Shikha Somani
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Book Description
Polymers undergo a sharp coil to stretch conformational transition in extension dominated flows when the strain rate exceeds a critical value. Dramatic change in flow behavior is known to occur at the coil-stretch transition, making it useful for several commercial applications. Despite decades of study, this phenomenon remains surrounded with controversy as the effect of solvent properties and fluid flow elements on this transition is not fully understood. In this work, we present a study of the coil-stretch transition and related hysteresis phenomenon using stochastic computer simulations. We first investigate the effect of solvent quality on the coil-stretch transition using Brownian dynamics simulations. Unlike experiments, which are plagued with problems related to polydispersity of polymers and inaccurate control over flow profiles, simulations offer a powerful platform to systematically study the effect of solvent quality while keeping all other parameters in the system constant. The system consists of a polymer subjected to planar elongational flow in both theta solvents and good solvents. The polymer is represented by a bead-spring chain model undergoing elongational flow. Solvent-mediated effects such as fluctuating hydrodynamic interactions (HI) and excluded volume (EV) are included rigorously. Conformational hysteresis is understood in terms of a 1-D energy landscape theory with an activation energy barrier for transition. At steady state, depending upon the flow rate, the energy landscape can either have one or two energy wells. An energy landscape with one well corresponds to the coiled state at low flow rate and stretched state at high flowrate. The double welled landscape corresponds to the hysteretic regime where both coiled and stretched conformational states coexist across the ensemble population. A key factor in determining the effect of solvent quality is the use of a proper measure of solvent quality. In almost all earlier studies, the effect of molecular weight on solvent quality has been neglected, producing inconsistent results. Here, the solvent quality is quantified carefully such that the effect of molecular weight and temperature is taken into account. Contrary to earlier findings, it is observed that with improvement in solvent quality, the chains unravel faster and the critical strain rate at which the coil to stretch transition takes place decreases. Furthermore, the solvent quality has a profound effect on the scaling of the critical strain rate with molecular weight and on both the transient and steady state properties of the system. Universal functions are shown to exist for the observed dynamic and static properties, which will prove useful in determining the operating parameters for experiments. In particular, the ratio of the two different relaxation times (longest relaxation time and zero shear rate viscosity) is found to be a universal function of solvent quality independent of molecular weight. The relaxation times (both the longest relaxation time and the zero shear rate viscosity) increase while the critical strain rate is found to decrease with solvent quality. Next, the study of conformational hysteresis is extended to more complicated 3-D flows to understand the effect of flow vorticity on this phenomenon. Heretofore, there has been no systematic methodology for studying the dynamical interactions between polymer molecules and elementary flow patterns in three-dimensional flows. Such a framework is essential not just for gaining valuable insights into the physics of complex fluids at a fundamental level, but it is also crucial for various important applications like turbulent drag reduction where the underlying physical mechanisms involve dynamical interactions between polymers and turbulence fine scale flow features. Such a study is presented here to provide a framework to interpret complex fluid phenomenon in terms of elementary flow patterns. We investigate the conformational hysteresis using rigorous Brownian dynamics simulations and specifically explore the effect of flow vorticity on the lifetime and width of the hysteresis window in 3-D flows. A systematic procedure is developed with careful eigenvalue analysis to explore the sole effect of vorticity on polymer dynamics keeping the principal strain rate fixed. It is observed that the hysteresis width shrinks due to increase in flow vorticity irrespective of the flow type (bi-extensional, bi-compressional, spiral-inwards, spiral-outwards etc). This is further traced to the alignment of eigenvectors with the principal eigenvector direction leading to enhanced fluctuations. Vorticity is found to have a significant effect on both the transient and the steady state properties. Understanding the effect of vorticity on polymer conformational hysteresis can further help in understanding the fundamental processes in complex flows.

Polymer Synthesis: Theory and Practice PDF

Author: Dietrich Braun
Publisher: Springer Science & Business Media
ISBN: 3642289800
Category : Technology & Engineering
Languages : en
Pages : 428

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Book Description
Emphasis is on a broad description of the general methods and processes for the synthesis, modification and characterization of macromolecules. These more fundamental chapters will be supplemented by selected and detailed experiments. In addition to the preparative aspects, the book also gives the reader an impression on the relation of chemical constitution and morphology of Polymers to their properties, as well as on their application areas. Thus, an additional textbook will not be needed in order to understand the experiments. The 5th edition contains numerous changes: In recent years, so-called functional polymers which have special electrical, electronic, optical and biological properties, have gained more and more in interest. This textbook was therefore supplemented by recipes which describe the synthesis of these materials in a new chapter "Functional polymers". Together with new experiments in chapter 3,4 and 5 the book now contains more than 120 recipes that describe a wide range of macromolecules. From the reviews of recent editions: "This is an excellent book for all polymer chemists engaged in synthesis research studies and education. It is educationally sound and has excellent laboratory synthetic examples. The fundamentals are well done for the teaching of students and references are resonably up-to-date. As in previous issues, there are sections dealing with an introduction; structure and nomenclature; methods and techniques for synthesis, characterization, processing and modification of polymers. ....The authors have noted the following changes from previous editions- a new section on correlations of structure, morphology and properties; revision and enlargement of other property and characterization procedures; additional new experiments such as controlled radical polymerization; enzymatic polymerizations; microelmulsions; and electrical conducting polymers. This is a high quality textbook at a reasonable price and should be considered as a suitable reference for all engaged in synthetic areas of polymer research." (Eli M. Pearce, Polytechnic University, Brooklyn, NY, USA)

Theoretical and Computational Studies of Solvent Effects on Complex Fluids PDF

Author: Govardhan Patluri Reddy
Publisher:
ISBN:
Category :
Languages : en
Pages : 154

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Book Description

Product Design and Testing of Polymeric Materials PDF

Author: Louise Ferrante
Publisher: CRC Press
ISBN: 1000715612
Category : Technology & Engineering
Languages : en
Pages : 576

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Book Description
Product Design and Testing of Polymeric Materials integrates polymer science principles with detailed experimental programs—helping engineers create optimal products. Thoroughly investigating both physical and processing properties of polymeric substances, this valuable guide presents the philosophy of product development management ... includes test methods for base property and end-use performance ... pairs viscometric and small-scale testing with molecular properties for processing advantages ... examines quality control from the laboratory to the marketplace ... applies the mechanics of experimental design to product optimization problems ... covers the mathematics needed for proper regression of experimental data ... and much more. Product Design and Testing of Polymeric Materials is a complete reference— defining numerous plastics and engineering terms and supplying important data on elastomers and plastics—and is an essential resource for polymer, plastics, and chemical engineers and scientists, materials scientists, and graduate-level students in these disciplines.

Author: Ulf Gedde
Publisher: Springer Science & Business Media
ISBN: 9780412626401
Category : Science
Languages : en
Pages : 326

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Book Description
This text provides a comprehensive overview of the physical characteristics of polymers from random polymer chains and the statistical concepts of a gaussian chain to crystalline polymers and their kinetics. The main part of the book is concerned with the different physical states and phenomena which are characteristic of polymers. A summary of the most important experimental methods in polymer physics is included. Each chapter provides the reader with problems, for which solutions are given at the end of the book.

Monte Carlo Simulation in Statistical Physics PDF

Author: Kurt Binder
Publisher: Springer Science & Business Media
ISBN: 366230273X
Category : Science
Languages : en
Pages : 201

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Book Description
When learning very formal material one comes to a stage where one thinks one has understood the material. Confronted with a "realiife" problem, the passivity of this understanding sometimes becomes painfully elear. To be able to solve the problem, ideas, methods, etc. need to be ready at hand. They must be mastered (become active knowledge) in order to employ them successfully. Starting from this idea, the leitmotif, or aim, of this book has been to elose this gap as much as possible. How can this be done? The material presented here was born out of a series of lectures at the Summer School held at Figueira da Foz (Portugal) in 1987. The series of lectures was split into two concurrent parts. In one part the "formal material" was presented. Since the background of those attending varied widely, the presentation of the formal material was kept as pedagogic as possible. In the formal part the general ideas behind the Monte Carlo method were developed. The Monte Carlo method has now found widespread appli cation in many branches of science such as physics, chemistry, and biology. Because of this, the scope of the lectures had to be narrowed down. We could not give a complete account and restricted the treatment to the ap plication of the Monte Carlo method to the physics of phase transitions. Here particular emphasis is placed on finite-size effects.