Predicting flow induced change in phase diagram of polymer solutions in simple shear flow

AbstractThe change in the phase diagram of polymer mixtures under flow is an important issue since flow may promote mixing or demixing of the phases in a polymer mixture. This work, compared to previous studies, presents a different approach with special attention to the rheology of polymer solutions and flow conditions. Different approaches including Marrucci's approach in calculating stored elastic free energy (ΔGE) have been reviewed. Marrucci’s equation is obtained based on a fundamental analysis of polymer chains microstructure. The new approach introduces the proper viscoelastic constitutive equations to estimate ΔGE. Selecting the appropriate rheological model is essential to correctly estimate the state of stress and deformation rates due to the flow. Moreover, the parameters of viscoelastic constitutive equations were defined, from the microstructural viewpoint, as functions of composition and temperature in semi-concentrated regions. Finally, flow induced change in the phase diagram of polymer solutions is predicted for a well-defined flow condition (constant shear rate and stress), and the results are compared with the previously reported experimental observations of mixing and demixing.

Download Full-text

Characterizing Polymer Surfaces and Interfaces

MRS Bulletin ◽

10.1557/s0883769400035168 ◽

1996 ◽

Vol 21 (1) ◽

pp. 49-53 ◽

Cited By ~ 8

Author(s):

T.R Russell

Keyword(s):

Spatial Distribution ◽

Polymer Chain ◽

Diblock Copolymers ◽

Surface Effects ◽

Polymer Chains ◽

Solid Polymer ◽

Polymer Mixture ◽

Interface Plane ◽

Polymer Mixtures ◽

Polymer Molecules

The presence of a surface or interface can markedly alter the configuration and spatial distribution of polymer molecules. In the bulk, polymer molecules—comprised of numerous monomers covalently linked together—pervade 10s of nanometers spatially. However, packing such chains at an interface—under the constraint that a solid polymer is essentially incompressible—necessitates perturbations to the chain configurations near the interface. This may result in a collapse of coils at the surface or in a preferential orientation of the monomers with respect to the interface plane. For amorphous homopolymers, however, simulations indicate that, on a segmental level, surface effects are generally damped within several segment diameters from the surface. Interactions between the surface and the polymer chains place additional constraints on the molecular configurations. As the architecture of the polymer chain becomes more complex, as with diblock copolymers in which two chemically distinct polymer chains covalently bond together at one end, the packing of chains at the interface must take into account the relative interactions of the two portions of the chains with the interface. Due to the connectivity of the blocks, preferential interactions of the blocks with the interface can influence the spatial distribution of the chains far from the interface. As the number of components increases, as with a simple binary-polymer mixture, not only must packing constraints be satisfied, but also the interactions of the two chains with the surface and with each other must be taken into account. In the case of homogeneous mixtures, the preferential interaction of one chain with an interface can lead to a substantial excess of that chain at the interface which, depending upon the proximity to the demixing point, can lead to surface effects that propagate many molecular diameters into the sample. The key, however, is the connectivity of the monomers in the polymer chain, which can enhance surface effects, as in the case of block copolymers or polymer mixtures, or suppress surface effects, as in the case of homopolymers.

Download Full-text

Fundamental Characteristics of Viscoelastic Fluids Simulated by a Bead-Spring-Damper Macro Model With Interaction

10.1115/imece2000-2705 ◽

2000 ◽

Author(s):

Takuji Ishikawa ◽

Nobuyoshi Kawabata ◽

Katsushi Fujita ◽

Yutaka Miyake

Keyword(s):

Normal Stress ◽

Constitutive Equations ◽

Viscoelastic Fluids ◽

Polymer Chains ◽

Viscoelastic Flow ◽

Simple Shear Flow ◽

Tetrahedral Structure ◽

Macro Model ◽

Normal Stress Differences ◽

Basic Characteristics

Abstract The flow field of viscoelastic fluids is commonly analyzed by using constitutive equations. In this paper, a bead-spring-damper macro model with interaction is proposed as an alternative to analyze a viscoelastic flow. A tetrahedral structure of beads and springs models a gathering of intertwined polymer chains. Behavior of the macro model and the cluster is computed under a simple shear flow condition. Shear-thinning of viscosity, the mechanism of generation of normal stress differences and the effect of slip in the interaction are investigated. The results show that the elongation of clusters to the x direction is the mechanism of the normal stress differences generation, and that the slip in the interaction weakens the stresses. Consequently, it is found that the bead-spring-damper macro model can express the behavior of polymer chains in viscoelastic fluids and basic characteristics of viscoelastic fluids without using constitutive equations.

Download Full-text

Specific volume and features of compressibility during the molding of powder-polymer mixtures with wax-polypropylene binder

All the materials Encyclopedic Reference Book ◽

10.31044/1994-6260-2019-0-9-25-33 ◽

2019 ◽

pp. 25-33

Author(s):

Alexander Muranov ◽

Alexey Semenov ◽

Anatoly Kutsbakh ◽

Boris Semenov

Keyword(s):

Phase Transition ◽

Comparative Analysis ◽

Powder Metallurgy ◽

Injection Molding ◽

Polymer Binder ◽

Polymer Mixture ◽

Powder Injection ◽

Polymer Mixtures ◽

Pvt Data ◽

Mathematical Processing

The article discusses one of the modern areas of powder metallurgy – the technology of manufacturing shaped parts by the powder injection molding (PIM). For the powder-polymer mixture (feedstock) with a wax-polypropylene binder of the solvent-thermal type of removal by isobaric volume dilatometry, the dependence of PVT state parameters was studied. For each component of the polymer binder, the dependence of pressure on the temperature of phase transition was obtained. As a result of mathematical processing and analysis of PVT data for the feedstock of the studied type, a technological window of parameters has been determined that allows injection molding of «green parts» with minimal volume shrinkage. The results of a comparative analysis of the compaction of feedstock with a polymer binder catalytic and solution-thermal type of removal are presented.

Download Full-text