Chapter 1 introduces the concept of Dual-Phase interactions and of “entanglement network” pursuant to the Cross-Dual-Phase model when the chain length reaches beyond a critical size; it defines the Dual-Phase rheological parameters that are found from fitting dynamic experimental data.
Chapter 2 explains what is “sustained-Orientation”, how it can be observed and the reasons why this new experimental evidence challenges the existing molecular models of polymer physics.
Chapter 3 compares experimental data and theory in the linear range and concludes that existing theories only appear to be successful in describing the linear viscoelastic data. In fact, if one closely analyzes the accuracy of the fits of classical expressions to experimental data, serious questions regarding the range of applicability of the classical formula arise. Is the concept of relaxation time limiting our analysis and comprehension of viscoelasticity when applied to the description of coupled interactive molecular motions?
Chapter 4 deals with the transient and the steady-state behavior of melts and studies non-linear effects at higher strain and/or shear rates. The main topic discussed is the experimental evidence of a strain induced time dependence of the viscoelastic functions triggered at relatively low strain (>15%) which current molecular dynamic models can only explain by ignoring the experimental evidence altogether or by calling it an artifact. The question we raise is to understand viscoelasticity from the standpoint of the local interactions of conformers, yet coupled with the question of the stability of the entanglement network (when there is one), i.e., in fact, to understand entanglements themselves. We suggest that the current molecular dynamic models of rheology are only adapted to the description of melt deformation in the linear regime, where entanglements are stable, yet become inadequate in the non-linear range of deformation, i.e. in the world encountered every day by all plastic processors manufacturing films, sheets, fibers and injection molded articles.
Chapter 5 considers the network of entanglement as an entity on its own, defined from the interactive coupling between conformers considered locally and globally, i.e. resulting from the competition between intra and intermolecular interactions for all macromolecules considered at once. We define the stress generated by such a network of phase-lines, either at rest (diffusion conditions), or under the influence of a gradient generated by deformation. The cohesive energy of the interactive conformers is linked to the frequency of diffusion of the phase-line network, providing a definition of the elasticity of the network (and thus of the stress, viscosity) from both a local and global perspectives. New analytical formulas are introduced to quantify these new concepts which no longer focus on the definition of a spectrum of relaxation times to explain viscoelastic behavior, in particular, shear-thinning and strain-softening.
Chapter 6: The Elastic Dissipative State of Polymeric Melts. Solid-Like Behavior in the Molten State
We report in this chapter the dynamic rheological properties of a typical amorphous polymer (polycarbonate) with no molecular particularities which would render the results unique to that polymer. We observed an increase of the viscosity at low w, as w -->0 (instead of a constant Newtonian viscosity) and a solid-like behavior for G’(w) and G”(w), which diverges from the classical rheological description accepted for a simple homopolymer melt. We offer an interpretation of this low w “shear-thinning tail” in terms of the Dual-Phase visco-elastic model of entanglements proposed in the previous chapters which suggest that the phase-line diffusion mechanism (the sweep of the phase lines) occurring in the Newtonian region is influenced by “b-grain glassification” occurring above Tg. Thus the viscosity increase at low w is essentially due to a “free volume” fluctuation decrease explaining the instability of the Newtonian state.
Chapter 7: Shear-Thinning of Polymeric Melts: the Failure of the Reptation Model.
Small angle neutron scattering (SANS) studies on polymer melt under steady-state flow provide in-situ information at a molecular scale on how the flow field is transmitted to the melt. Such experiments, called "Rheo-SANS”, are difficult to set up and require special equipment but their results are fundamental to test experimentally the accepted claim by the reptation model that the shear-thinning of entangled polymer chains is due to the significant orientation of the segments between entanglements under the shear flow.
We report two significant Rheo-SANS studies, one by Watanabe et al. in Japan, published in 2007, and the other one by Noirez et al. in France, published in 2009. Both studies concluded that the chains remain largely undeformed under steady-state shear flow conditions for which extensive shear-thinning was present. These results represent a formidable challenge to the reptation model of melt deformation.
Chapter 8 CONCLUSIONS. Entanglements: A New Interpretation and Its Perspectives In Science and Technology.
The current understanding of polymer physics is based on the description of the properties of a single chain embedded in a sea of average interaction from the other chains that disturbs its properties. For instance, in the case of rubber extensibility, one calculates the variation of the chain entropy with strain by determination of the average rms end to end distance characteristic of the equilibrium macromolecular coil assumed by the chain. The statistics at a molecular level is treated from a pure macromolecular perspective.
In the type of research examined in this book the statistical system is no longer a single macromolecule made up of covalently interactive conformers, although this situation is also studied; the system is the global set of conformers belonging to all macromolecules considered collectively. The influence generated by the other molecules on the configurational properties of a single chain (defining its entropy and enthalpy) is no longer a mean-field but a “granular-field” that considers the existence of an inhomogeneous density of state due to local fluctuations of the interactions. The role of the elastic dissipative phase-wave is to homogenize the local fluctuations’ heterogeneous density. The evolution with time of the state of interactions between the conformers, when the system is submitted to a mechanical force or to a temperature variation, describes the change of the physical properties. This new statistics leads to the elaboration of a different understanding of visco-elasticity, rubber elasticity, and of the concept of entanglement of the macromolecules. This last chapter of the book illustrates with a few examples the applications of the new paradigm: the lowering of melt viscosity before molding or compounding by “disentanglement” and the preparation of “plastic-fuel battery” materials from recycled plastics.
New Book "Physics of Polymer Interactions: a New Approach. Applications to Rheology and Processing".
Table of Contents
Preface : 40 YEARS OF PAINTING ON THE SAME CANVAS
Chapter 1: PREAMBLE: INTRODUCTION TO THE DUAL-PHASE MODEL OF POLYMER INTERACTIONS AND CROSS-DUAL-PHASE MODEL OF ENTANGLEMENTS
Chapter 2: THE TROUBLE WITH POLYMER PHYSICS: “SUSTAINED-ORIENTATION”
Chapter 3: THE GREAT MYTHS OF POLYMER RHEOLOGY, PART 1: COMPARING THEORY WITH EXPERIMENTAL DATA
Chapter 4: THE GREAT MYTHS OF POLYMER RHEOLOGY, PART 2: TRANSIENT AND STEADY STATE- STABILITY OF THE NETWORK OF ENTANGLEMENT
Chapter 5: THE GREAT MYTHS OF POLYMER RHEOLOGY, PART 3: ELASTICITY OF THE NETWORK OF ENTANGLEMENTS
Chapter 6: THE ELASTIC DISSIPATIVE STATE OF POLYMERIC MELTS: SOLID-LIKE BEHAVIOR IN THE MOLTEN STATE
Chapter 7: SHEAR-THINNING OF POLYMERIC MELTS: THE FAILURE OF THE REPTATION MODEL
Chapter 8: ENTANGLEMENTS: A NEW INTERPRETATION AND ITS PERSPECTIVES IN SCIENCE AND TECHNOLOGY
New Book "Physics of Polymer Interactions: a New Approach. Applications to Rheology and Processing".
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