Newtonian Polymer Research Articles

Wire coating and melt elasticity

In modern wire coating, the polymer is dragged through a round cylindrical die. Onto this drag flow, we superpose pressure-driven extrusion. We devote this paper to analyzing this extrusion in eccentric cylindrical coordinates. We find that, when the molten polymer is an elastic liquid, a recentring force, Fx, is exerted on the wire. This is how the wire is then coated concentrically. The lateral force acting on the wire thus matters. This also explains why the wire cannot be coated with Newtonian or nearly Newtonian polymer. The axial force on the wire, Fz, is always positive, and we find that the die eccentricity decreases Fz. This determines the required pulling force. Thus, the axial force acting on the wire also matters. We follow the method of Jones (1964) called polymer process partitioning, to obtain the coating velocity profile, v⌣z(ξ,θ), from which we get the coating thickness profile. We integrate this profile to get the flow rate, and thus, the average thickness. We also obtain the stresses in the extrudate. We include one detailed dimensional worked example to help engineers design coating dies.

New insights on the layer uniformity of multilayered films produced by coextrusion with interfacial surface generators

AbstractPolymer coextrusion is a manufacturing process whereby at least two polymer melts feed a die to form an extrudate made up of different layers, typically up to 12, to achieve a better product performance. Extruded films with hundreds or thousands of layers can be produced by using sequences of layer multipliers, also known as interfacial surface generators (ISG), at the die inlet. Each ISG splits, stacks, and merges the flow by means of various geometrical channel transformations (GT), in such a way that the number of layers at the outlet is doubled. However, in practice, the thicknesses of the individual layers generated after each transformation are often non‐uniform. This work deals with the numerical simulation of multilayer co‐extrusion of Newtonian polymer melts, aiming at providing new insights on the influence of the ISG geometry on the layer uniformity. It was found that depending on the combination of GT taking place, uneven layers may form due to the development of unsymmetrical velocity profiles along the direction perpendicular to the fluid interface. From this information, improved ISG dies, capable of producing coextruded films with uniform layer distribution, are proposed and assessed numerically.Highlights The polymer coextrusion process produces multilayer products. Extruded films can be produced using Interfacial surface generators (ISG). Polymers flow through ISG by several channel geometric transformations (GTs). Polymer melts flow through ISG undergoing various channel geometric transformations (GTs). Non‐uniform layers can be generated in the ISG. ISG performance can be improved when GTs are thoughtfully combined.

Viscoelasticity enhances collective motion of bacteria.

Bacteria form human and animal microbiota. They are the leading causes of many infections and constitute an important class of active matter. Concentrated bacterial suspensions exhibit large-scale turbulent-like locomotion and swarming. While the collective behavior of bacteria in Newtonian fluids is relatively well understood, many fundamental questions remain open for complex fluids. Here, we report on the collective bacterial motion in a representative biological non-Newtonian viscoelastic environment exemplified by mucus. Experiments are performed with synthetic porcine gastric mucus, natural cow cervical mucus, and a Newtonian-like polymer solution. We have found that an increase in mucin concentration and, correspondingly, an increase in the suspension's elasticity monotonously increases the length scale of collective bacterial locomotion. On the contrary, this length remains practically unchanged in Newtonian polymer solution in a wide range of concentrations. The experimental observations are supported by computational modeling. Our results provide insight into how viscoelasticity affects the spatiotemporal organization of bacterial active matter. They also expand our understanding of bacterial colonization of mucosal surfaces and the onset of antibiotic resistance due to swarming.

Electro-orientation of Ag nanowires in viscoelastic fluids

In this work we study the electro-orientation (through electric birefringence experiments) of silver nanowires in polymer solutions eventually capable of forming gel networks. Information on the structure of the polymer solution is obtained by evaluating the electro-orientation of the nanowires. It is found that in presence of poly(ethylene oxide), Kerr’s law (birefringence proportional to the square of the field) is fulfilled, and the randomization process after switching off the external field is purely diffusive, controlled by the viscosity of the Newtonian polymer solution. In the case of (gelating) sodium alginate solutions, measuring at larger distances from the bottom (where the source of cross-linking Ca2+ ions is deposited) means a smaller degree of cross-linking, and a less stiff gel. In fact, it is found that after a certain time the birefringence signal gets frozen at the bottom, indicating that a gel network is formed which hinders particle orientation. The viscosity deduced up to that point agrees well with rheological determinations, with increasing deviations found at longer times due to the inhomogeneous gel formation. This process has an interesting consequence on birefringence response: Kerr’s law fails to be fulfilled, appearing a “yield” applied electric field, larger the longer the time after preparation.

The Impact of Rheology on Viscous Oil Displacement by Polymers Analyzed by Pore-Scale Network Modelling.

Several experimental studies have shown significant improvement in heavy oil recovery with polymers displaying different types of rheology, and the effect of rheology has been shown to be important. These experimental studies have been designed to investigate why this is so by applying a constant flow rate and the same polymer effective viscosity at this injection rate. The types of rheology studied vary from Newtonian and shear thinning behavior to complex rheology involving shear thinning and thickening behavior. The core flood experiments show a significantly higher oil recovery with polyacrylamide (HPAM), which exhibits shear thinning/thickening behavior compared to biopolymers like Xanthan, which is purely shear thinning. Various reasons for these observed oil recovery results have been conjectured, but, to date, a clear explanation has not been conclusively established. In this paper, we have investigated the theoretical rationale for these results by using a dynamic pore scale network model (DPNM), which can model imbibition processes (water injection) in porous media and also polymer injection. In the DPNM, the polymer rheology can be shear thinning, shear thinning/thickening, or Newtonian (constant viscosity). Thus, the local effective viscosity in a pore within the DPNM depends on the local shear rate in that pore. The predicted results using this DPNM show that the polymer causes changes in the local flow velocity field, which, as might be expected, are different for different rheological models, and the changes in the velocity profile led to local diversion of flow. This, in turn, led to different oil recovery levels in imbibition. However, the critical result is that the DPNM modelling shows exactly the same trend as was observed in the experiments, viz. that the shear thinning/thickening polymer gave the highest oil recovery, followed by the Newtonian Case and the purely shear thinning polymer gave the lowest recover, but this latter case was still above the waterflood result. The DPNM simulations showed that the shear-thinning/thickening polymer show a stabilized frontal velocity and increased oil mobilization, as observed in the experiments. Simulations for the shear-thinning polymer show that, in high-rate bonds, the average viscosity is greatly reduced, and this causes enhanced water fingering compared to the Newtonian polymer case. No other a priori model of the two-phase fluid physics of imbibition, coupled with the polymer rheology, has achieved this degree of predictive explanation, of these experimental observations, to our knowledge.

The effect of the viscosity ratio on band formation in sheared mixtures of phase-separated polymer solutions with ultralow interface tension

The microscopic structure and dynamics of droplet dispersions formed by phase separation of two Newtonian polymer solutions were observed under simple shear. The phases had equal volumes. Under certain conditions, these dispersions show long, wormlike, extended structures after several minutes of shearing. The development of these structures was recorded in microscopic movies. These were interpreted by calculating two-point grey value correlation functions. The divergence of the correlation in the flow direction was taken as a signature of the onset of the extended structures. It was demonstrated that a viscosity ratio far from the unity of the two phases is necessary for the formation of the long shear-stabilised structures. At a viscosity ratio close to unity, the systems maintain isolated droplets in a dynamic equilibrium of coalescence and break-up. The structure formation is the result of shear-induced coalescence. The need for a difference in viscosity between the phases suggests a relation with shear banding seen in shear-thinning systems.

Analysis of coherent structures in drag-reducing polymer solution flow based on proper orthogonal decomposition

Direct numerical simulation (DNS) of forcing homogeneous isotropic turbulence with polymers was performed. In order to understand the polymers effect on turbulent coherent structures, proper orthogonal decomposition was performed to identify coherent structures based on DNS data, so as to analyze the remarkable difference due to the addition of polymers. The results showed that the numbers for eigenmodes required for capturing coherent structures were 32 and 24 for the Newtonian fluid and polymer solution flows, respectively, which means the decrease of the complexity in polymer solution flow. Through the POD energy spectrum, it was found that the turbulent kinetic energy is distributed onto a large number of eigenmodes whether in the Newtonian fluid flow or polymer solution flow, suggesting that polymer solution flow is still turbulent in one aspect. Besides, the POD eigenmodes were investigated, which found that the small-scale structures are inhibited in polymer solution flow.

X-ray scattering measurements of particle orientation in a sheared polymer/clay dispersion

We report steady and transient measurements of particle orientation in a clay dispersion subjected to shear flow. An organically modified clay is dispersed in a Newtonian polymer matrix at a volume fraction of 0.02, using methods previously reported by Mobuchon et al. (Rheol Acta 46: 1045, 2007). In accord with prior studies, mechanical rheometry shows yield stress-like behavior in steady shear, while time dependent growth of modulus is observed following flow cessation. Measurements of flow-induced orientation in the flow-gradient plane of simple shear flow using small-angle and wide-angle X-ray scattering (SAXS and WAXS) are reported. Both SAXS and WAXS reveal increasing particle orientation as shear rate is increased. Partial relaxation of nanoparticle orientation upon flow cessation is well correlated with time-dependent changes in complex modulus. SAXS and WAXS data provide qualitatively similar results; however, some quantitative differences are attributed to differences in the length scales probed by these techniques.

Dynamic wetting with viscous Newtonian and non-Newtonian fluids

We examine various aspects of dynamic wetting with viscous Newtonian andnon-Newtonian fluids. Rather than concentrating on the mechanisms that relieve the classiccontact line stress singularity, we focus on the behavior in the wedge flow near the contactline which has the dominant influence on wetting with these fluids. Our experiments showthat a Newtonian polymer melt composed of highly flexible molecules exhibits dynamicwetting behavior described very well by hydrodynamic models that capture the criticalproperties of the Newtonian wedge flow near the contact line. We find that shear thinninghas a strong impact on dynamic wetting, by reducing the drag of the solid on the fluid nearthe contact line, while the elasticity of a Boger fluid has a weaker impact on dynamicwetting. Finally, we find that other polymeric fluids, nominally Newtonian inrheometric measurements, exhibit deviations from Newtonian dynamic wettingbehavior.

Rheo‐optical study of nonlinear effects in an immiscible Newtonian polymer blend under large amplitude oscillatory shear flow

AbstractThe morphology evolution of polydimethylsiloxane (PDMS) drops embedded in polyisobutylene (PIB) matrix blend was investigated under large amplitude oscillatory shear flow (LAOS) using rheo‐optical techniques. The oscillatory shear experiments were carried out at various frequencies and deformation amplitudes up to 800%. The drop deformation was assessed by optical microscopy, small angle light scattering (SALS), and linear‐dichroism. It was observed that when the flow is reversed, the drop returns back to its equilibrium spherical shape and then it deforms again symmetrically in the other direction, with exactly the same angle θ. However, when the deformation amplitude increases, various unusual behaviors have been observed and upon reversal of the flow in the opposite direction during oscillations, the drop does not reach the spherical equilibrium shape anymore at the flow reversal point but it rather adopts an ellipsoidal shape as was predicted by Yu et al. model.3 Such a behavior was assessed by both optical microscopy observations and by optical techniques. When the deformation was further increased, the drops undergo break‐up process and the break‐up point was assessed by optical techniques. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1467–1480, 2009

Band formation on shearing in phase-separated polymer solutions

In a phase-separated mixture of two Newtonian polymer solutions sheared in a cone-plate geometry adapted for microscopic observation at a zero-velocity plane, shear-induced coalescence of droplets of the broken-up phase, followed by band formation, was observed. Initially wormlike structures developed into doughnut-shaped bands, disconnected from the walls of the geometry. The shear rate and composition inside the bands differed from that in the outside solution. The shear-shear rate instability preceding the band formation could be qualitatively described by a van der Waals-loop-shaped shear rate dependence of droplet deformation.

3D Numerical Modelling of a Dip-coating Process by a Multidomain Macroscopic Approach

The hot dip-coating process is numerically studied on the bases of a 3D strongly coupled thermomechanical model. At the macroscopic scale, the process is described as a solidification of a hot Newtonian polymer solution on the surface of a cold mould moving in/out of the bath. The evolution of the temperature of the liquid around the mould and of the thickness of solid phase is governed by equations resulting from thermomechanics. The prediction of the solidified phase thickness is ensured by using a characteristic function which reflects the state of the solution (liquid or solid). A mixed finite element method with multidomain approach is developed in order to simulate the average growth rate of solidified layer during the dip-coating process and to characterize the influence of the velocity of the mould motion on its the thickness.

Analysis of morphology development in immiscible Newtonian polymer mixtures during shear flow

The aim of this work was to investigate the influence of morphology evolution in immiscible blends of Polyisobutene/(Polydimethylsiloxane) on their rheological properties both in steady and transient states under linear and nonlinear flow regimes. The focus was made on the region below the critical shear rate of drops breakup. Such critical shear rate was determined experimentally through a new route using small angle light scattering technique. Interfacial shear stress, first normal stress difference and shear viscosity of the blend were measured in steady shear regime below the critical shear rate and the obtained results were compared to the predictions of the model of Yu et al. [Yu, W., M. Bousmina, M. Grmela, and C. Zhou, “Modeling of oscillatory shear flow of emulsions under small and large deformation field,” J. Rheol. 46, 1401–1418 (2002a) and Yu, W., M. Bousmina, M. Grmela, J. F. Palierne, and C. Zhou, “Quantitative relationship between rheology and morphology in emulsions,” J. Rheol. 46, 1381–13...

Microstructural evolutions of LDPE/PA6 blends by rheological and rheo-optical analyses: Influence of flow and compatibilizer on break-up and coalescence processes

In this paper we investigate the relationships between flow and morphology in immiscible diluted non-Newtonian (LDPE and PA6) blends. Both rheological and rheo-optical techniques have been used. The effect of a steady shear flow on the blend microstructure has been studied at various shear rates. Moreover, the effects of a compatibilizing agent on rheology and morphology have been analysed. The compatibilizer causes decrease of average drop sizes and stabilization of the blend morphology during a steady shear flow. An attempt to relate the evolution of the volume-average radius with flow has been carried out by following the approach generally pursued for Newtonian polymer blends. The rescaling of both the capillary number and the viscosity ratio by using the shear-rate-dependent viscosity of blend constituents allows to roughly estimate the shear rate wherein severe drop break-up phenomena occur for the uncompatibilized system. Conversely, quantitative discrepancies between experimental data and theoretical expectations have been found for compatibilized blend. The coarsening behaviour in the early stages of an annealing process at rest has been studied, and simple model has been proposed to describe the volume average drop radius growth rate. The coalescence suppression detected for the compatibilized blend could be due to the shielding effect related to the presence of the copolymer layers at the interface between the phases.

Intensification of Heat and Mass Transfer Processes in the Working Channel of Extrusion Machines during Processing of Newtonian Polymer Liquids

Intensification of Heat and Mass Transfer Processes in the Working Channel of Extrusion Machines during Processing of Newtonian Polymer Liquids

Loss of surface and volume electrical conductivities in polymer compounds due to shear‐induced migration of conductive particles

AbstractThe loss of surface and volume electrical conductivities of conductive polymer compounds as a result of shear‐induced migration of conductive filler particles is elucidated with the help of model equations by considering flow of uniformly mixed conductive polymer compounds through two‐dimensional channels, as in injection molding or extrusion of sheets and films. Matrix polymers of shear‐thinning nature and non‐colloidal conductive particles of spherical shape are considered. The effect of particle migration is found to be most severe in the case of compositions around the percolation threshold—an otherwise uniformly mixed conductive compound turns into an insulator because of migration of conductive particles from the surface to the bulk. In addition, the extent of migration of particles and consequently the loss of conductivity are found to be the greatest for Newtonian polymer matrices, where the gradients of shear stress are the highest. The extent of migration gradually reduces as the polymer becomes more shear‐thinning.

Apparatus-specific analysis of fluid adhesion measurements

A thin film of viscous liquid between two solids acts as an adhesive due to the large force resisting separation of the solids. This effect is exploited in pressure-sensitive adhesive bonds. One method of investigating such bonds is to use a probe tack test in which a rigid probe is indented into a thin adhesive layer coating a rigid flat base. These experiments are characterized by two quantities: the total work of separation, that is, the work done in extracting the rigid punch from the adhesive film, and the peak adhesive force, otherwise known as the adhesive strength. Little effort, however, has been spent on understanding the connection between these quantities and the apparatus used to measure them. In this article we shall study the simplest case of fluid adhesion where a spherical probe and flat are bound by a high viscosity Newtonian polymer melt (polydimethylsiloxane or polybutene) and examine the role of apparatus-specific parameters in determining the measured adhesive strength and work of separation. We shall show how a dimensionless master-curve can be derived to capture the dependence of the adhesive strength on the testing regime. Specific attention is paid to the effect of system compliance on the adhesion, as introduced by the presence of a compliant load cell used to measure the adhesive force. A relationship linking the adhesive strength of a Newtonian film and the work of separation is also presented.

On the flow of non-Newtonian polymer solutions

This paper presents a study of the flow of non-Newtonian polymer solutions. The predictions obtained by a numerical technique are compared with a derived analytical solution and with experimental measurements. Poly(vinyl chloride) (PVC) solutions in cyclohexanone were prepared in the concentration range between 16.67 and 20.24% w/w to determine the shear viscosity functions by means of a Brookfield RVT viscometer. A computer code was employed to simulate the laminar flow of a 20% w/w solution in a pipe. Results for the fully developed flow are in excellent agreement with the derived analytical solution and are also verified experimentally by measuring fluid velocity in a real pipe, using a laser-Doppler anemometer. Furthermore, the laminar flow of a Newtonian and an Ellis fluid in a pipe as well as the flow of a power law fluid in a sudden enlargement are simulated with the same code, giving predictions consistent with theory. It is concluded that computer simulation is a powerful and accurate technique for predicting the flow behavior of non- Newtonian polymer solutions.

Experimental modelling of mantled porphyroclasts

Mantled porphyroclasts are commonly used as sense of shear indicators in mylonites. Analogue experiments have been carried out to model the development of such objects. Rigid spheres mantled by a viscous Plasticene-putty mixture with power-law behaviour were suspended in an optically transparent Newtonian polymer matrix. The samples were deformed between two cylinders, one placed within the other, and with coinciding axes. This induces a non-coaxial flow between the cylinders and allows the achievement of high finite strain. The viscous mantle around the rigid sphere remained undeformed, deformed into an ellipsoid, or developed wings. The final geometry depends mainly on the induced viscosity contrast between the mantle and the matrix, which is a function of the flow-induced stress on the surface of the mantle. Winged mantles only develop if the induced viscosity contrast between the mantle and the matrix polymer is sufficiently small. If this ‘critical’ induced viscosity contrast is exceeded, the mantled sphere remains undeformed or obtains a stable ellipsoidal shape, even at high finite strain. σ-shaped winged mantles only develop in simple shear flow if the mantle around a rigid sphere is thin.

Structural Foam Molding: Modeling of Bubble-Growth Process Resulting from Chemical Blowing Agents

Abstract A mathematical model of the thermoplastic structural foam molding process utilizing a chemical blowing agent is described. First, an analytical solution of bubble growth in a Newtonian polymer melt is developed for isothermal conditions by neglecting the inertial and surface tension effects. Next, a numerical scheme for the solution of the nonisothermal case is developed by introducing a heat conduction equation including the reaction heat of chemical blowing agent decomposition. the effects of processing parameters such as processing temperature, concentration of blowing agent, and kinetics of decomposition reaction of blowing agent are discussed through numerical computations.