Polymer Dynamics In Dilute Media

Download or read book Polymer Dynamics in Dilute Media written by Shikha Somani and published by Stanford University. This book was released on 2011 with total page 135 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book The Theory of Polymer Dynamics written by Masao Doi and published by Oxford University Press. This book was released on 1988 with total page 420 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book provides a comprehensive account of the modern theory for the dynamical properties of polymer solutions. The theory has undergone dramatic evolution over the last two decades due to the introduction of new methods and concepts that have extended the frontier of theory from dilute solutions in which polymers move independently to concentrated solutions where many polymers converge. Among the properties examined are viscoelasticity, diffusion, dynamic light scattering, and electric birefringence. Nonlinear viscoelasticity is discussed in detail on the basis of molecular dynamical models. The book bridges the gap between classical theory and new developments, creating a consistent picture of polymer solution dynamics over the entire concentration range.

Download or read book Phenomenology of Polymer Solution Dynamics written by George D. J. Phillies and published by Cambridge University Press. This book was released on 2011-10-06 with total page 527 pages. Available in PDF, EPUB and Kindle. Book excerpt: Presenting a completely new approach to examining how polymers move in non-dilute solution, this book focuses on experimental facts, not theoretical speculations, and concentrates on polymer solutions, not dilute solutions or polymer melts. From centrifugation and solvent dynamics to viscosity and diffusion, experimental measurements and their quantitative representations are the core of the discussion. The book reveals several experiments never before recognized as revealing polymer solution properties. A novel approach to relaxation phenomena accurately describes viscoelasticity and dielectric relaxation and how they depend on polymer size and concentration. Ideal for graduate students and researchers interested in the properties of polymer solutions, the book covers real measurements on practical systems, including the very latest results. Every significant experimental method is presented in considerable detail, giving unprecedented coverage of polymers in solution.

Download or read book Introduction to Polymer Dynamics written by Pierre-Gilles de Gennes and published by CUP Archive. This book was released on 1990-09-20 with total page 72 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book, based on lectures given at the Polytechnic of Milan, gives a broad overview of the field of polymer dynamics. In these lectures the aim is to stress the fundamental concepts of the behaviour of polymers without drawing on the more advanced mathematical formalism which often obscures the natural elegance of the subject matter. Professor De Gennes is one of the most distinguished workers in the field of material science. Therefore this book will be welcomed by both the experienced researcher in the area and the interested layman. It will be of particular value to graduate students.

Download or read book Polymer and Cell Dynamics written by Wolfgang Alt and published by Birkhäuser. This book was released on 2012-12-06 with total page 306 pages. Available in PDF, EPUB and Kindle. Book excerpt: Polymer and cell dynamics play an important role in processes like tumor growth, metastasis, embryogenesis, immune reactions and regeneration. Based on an international workshop on numerical simulations of polymer and cell dynamics in Bad Honnef (Germany) in 2000, this volume provides an overview of the relevant mathematical and numerical methods, their applications and limits. Polymer and Cell Dynamics will be of interest to scientists and advanced undergraduates.

Download or read book The Mesoscopic Theory of Polymer Dynamics written by Vladimir N. Pokrovskii and published by Springer Science & Business Media. This book was released on 2009-12-16 with total page 256 pages. Available in PDF, EPUB and Kindle. Book excerpt: The theory presented in this book explains in a consistent manner all dynamics effects observed in very concentrated solutions and melts of linear polymers from a macromolecular point of view. The presentation is compact and self-contained.

Download or read book The Mesoscopic Theory of Polymer Dynamics written by Vladimir Nikolaevich Pokrovskiĭ and published by Springer Science & Business Media. This book was released on 2000 with total page 243 pages. Available in PDF, EPUB and Kindle. Book excerpt: Our brutal century of atom bombs and spaceships can also be called the century ofpolymers. In any case, the broad spreading ofsynthetic polymer materials is one of thesigns of our time. A look at the various aspects of our life is enough to convince us that polymeric materials (textiles, pl- tics, rubbers) are as widely spread and important in our life as are other materials (metals and non-metals) derived from small molecules. Polymers have entered the life of the twentieth century as irreplaceable construction materials. Polymers differ from other substances by the size of their molecules which, appropriately enough, are referred to as macromolecules, since they consist of thousands or tens of thousands of atoms (molecular weight up to -4 6 10 ormore) andhave a macroscopic rectilinear length (upto 10 cm). The atoms ofa macromolecule are firmly held together by valence bonds, fo- ing a single entity. In polymeric substances, the weaker van der Waals forces have an effect on the components of the macromolecules which form the system. The structure of polymeric systems is more complicated than that oflow-molecular solids or liquids, but there are some common features: the atoms within a given macromolecule are ordered, but the centres ofmass of the individual macromolecules and parts of them are distributed randomly. Remarkably, the mechanical response of polymeric systems combines the elasticity of a solid with the fluidity of a liquid.