Hypothesis on a Certain Flow Instability in Polymer Melts

Huseby, T. W.

doi:10.1122/1.549056

Cited by 56 publications

(18 citation statements)

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“…Polymer melts [14] Constitutive instability Many-valued shear stress [79] Constitutive instability Predicts hysteresis loop [59] Junctions are assumed between wall/polymer interface as well as in the bulk of the polymer fluid. Junctions are described by kinetic equation describing a reaction between bonded and free macromolecules at the interface Prediction of the temperature dependence of wall-slip velocities.…”

Section: Reference Approach Predictionmentioning

confidence: 99%

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Slipping fluids: a unified transient network model

Joshi

Lele

Mashelkar

2000

Journal of Non-Newtonian Fluid Mechanics

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Wall slip in polymer solutions and melts play an important role in fluid flow, heat transfer and mass transfer near solid boundaries. Several different physical mechanisms have been suggested for wall slip in entangled systems. We look at the wall slip phenomenon from the point of view of a transient network model, which is suitable for describing both, entangled solutions and melts. We propose a model, which brings about unification of different mechanisms for slip. We assume that the surface is of very high energy and the dynamics of chain entanglement and disentanglement at the wall is different from those in the bulk. We show that severe disentanglement in the annular wall region of one radius of gyration thickness can give rise to non-monotonic flow curve locally in that region. By proposing suitable functions for the chain dynamics so as to capture the right physics, we show that the model can predict all features of wall slip, such as flow enhancement, diameter-dependent flow curves, discontinuous increase in flow rate at a critical stress, hysteresis in flow curves, the possibility of pressure oscillations in extrusion and a second critical wall shear stress at which another jump in flow rate can occur. #

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Section: Reference Approach Predictionmentioning

confidence: 99%

“…This mechanism is related to a non-monotonic stress-strain rate relationship [14]. Doi±Edwards theory predicts that stress passes through a maximum and then decreases with a further increase in the shear rate, which leads to mechanical instability in steady shearing [27].…”

Section: Introductionmentioning

confidence: 99%

Slipping fluids: a unified transient network model

Joshi

Lele

Mashelkar

2000

Journal of Non-Newtonian Fluid Mechanics

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“…This work is based on the concept set forth by Huseby [27,28] based on occurence of a relaxation function maximum in the region of transition from the terminal zone to the high-elasticity plateau. Knowing the relaxation spectrum of the polymer and using Pao's theory [29][30][31], Huseby was able to calculate the flow curve as well as the relationship between recoverable (high-elastic) strain and flow rate.…”

Section: Introductionmentioning

confidence: 99%

The rheological behavior of flexible-chain polymers in the region of high shear rates and stresses, the critical process of spurting, and supercritical conditions of their movement at T > Tg

1984

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Methods of capillary viscometry were used in studying the rheological properties and behavior of a broad range of rubbers, including polymers with narrow and wide molecular-weight-distribution as well as commercial rubber grades, at widely varying shear rates and stresses. As is shown, in full conformity with the previously conducted experiments, during transition from a fluid to highelastic (quasi-cross-linked) state, they are chracterized by spurting followed by sliding over the channel walls. This relaxation transition is characterized by a critical shear stress value invariant with respect to the molecular weight, molecularweight distribution and temperature. The parameters defining spurting of polymer flow as a function of molecular-weight characteristics, temperature, and channel geometry have been investigated in detail. It is shown for the first time that under supercritical conditions the rate of polymer flow through channels does not depend, in the first approximation, on the molecular weight of the polymer, its molecularweight distribution, temperature, and filling, but is determined only by the shear stress.

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“…Huseby (1966) proposed that if the curve of shear stress versus shear rate in steady simple shear has a maximum followed by a minimum, this would imply that a given shear stress could be supported by two different shear rates. This opens the door to the possibility that in pressure flow there could be a discontinuity in the shear rate profile y(r) in the capillary, with a layer of higher shear rate nearer the wall.…”

Section: Rheological Explanations Of Oscillatory Flowmentioning

confidence: 99%

Role of slip and fracture in the oscillating flow of HDPE in a capillary

Hatzikiriakos

Dealy

1992

Journal of Rheology

196

123

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Certain polymers exhibit two distinct branches in their capillary flow curves (wall shear stress versus apparent wall shear rate). This gives rise to oscillatory flow in constant-piston-speed rheometers and to flow curve hysteresis in controlled-pressure rheometers. These curious phenomena have attracted considerable interest over a period of many years, but their basic mechanisms are still the subject of debate. Building on previous work we have developed a model that predicts all the essential features of the curves of pressure and flow rate versus time in the oscillatory flow regime. Fluid compressibility and the second branch of the flow curve are necessary features of the model, but fluid elasticity is found not to be an essential element. While our macroscopic measurements do not prove it conclusively, our data lead us to believe that on the high-flow-rate branch of the flow curve there is slip along a cylindrical fracture surface near the wall. The jump to the high-flow branch occurs when this fracture occurs, at an upper critical value of the shear stress, while the jump back to the low-flow branch occurs when adhesion is established at the fracture surface at a lower critical shear stress.

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Hypothesis on a Certain Flow Instability in Polymer Melts

Cited by 56 publications

References 0 publications

Slipping fluids: a unified transient network model

Slipping fluids: a unified transient network model

The rheological behavior of flexible-chain polymers in the region of high shear rates and stresses, the critical process of spurting, and supercritical conditions of their movement at T > Tg

Role of slip and fracture in the oscillating flow of HDPE in a capillary

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