- Experimental Study and Modelling of Oscillating Flow of High
Density Polyethylenes
- V. Durand, B. Vergnes, J.F. Agassant, E. Benoit, and R.J. Koopmans
- Rheometry and Detection of Apparent Wall Slip for Poiseuille
Flow of Polymer Solutions and Particulate Dispersions by NMR Velocimetry
- Stephen J. Gibbs, Kieran L. James, Laurance D. Hall, Derek E. Haycock, William J. Frith,
and Stephen Ablett
- Thermodynamic Considerations on the Electro-Rheology of
Non-colloidal Suspensions
- Davide A. Hill
- The Generalised Engineering Bernoulli Equation [GEBE], and
the First and Second Laws of Thermodynamics, for Viscoelastic Fluids
- Gianni Astarita and Michael E. Mackay
- Out-of-Plane Orientational Dynamics of Polymer Liquid
Crystals Under Flow
- N. C. Andrews, A. J. McHugh and B. J. Edwards
- Anomalies in the Normal Force Measurement when Using a
Force Rebalance Transducer
- Jan M. Niemiec, Jean-Jacques Pesce, and Gregory B. McKenna, Stephen Skocypec, and Ronald
F. Garritano
- Influence of a Nonionic Surfactant on the Rheology of a
Hydrophobically Associating Water Soluble Polymer
- Thierry Aubry and Michel Moan
- On the Stability of Molecular Weight Distributions As
Computed from the Flow Curves of Polymer Melts
- M.R. Nobile, F. Cocchini, and J.V. Lawler
- Flow Characteristics of Concentrated Emulsions of Very
Viscous Oil in Water
- Gustavo A. Núñez, Maria Briceño, Clara Mata, Hercilio Rivas and Daniel D. Joseph
- The Effect of Blending Particles with Different
Conductivity on Electrorheological Properties
- Ryo Sakurai, Howard See, and Tasuku Saito
- Influence of Amylose Content on the Viscous Behavior of
Low Hydrated Molten Starches
- G. della Valle, P. Colonna, A. Patria, and B. Vergnes
Experimental Study and Modelling of Oscillating Flow of High Density
Polyethylenes
V. Duranda), B. Vergnesb), J.F. Agassant,
CEMEF, Ecole des Mines de Paris, URA CNRS 1374, BP 207, 06904 Sophia-Antipolis, France
E. Benoit,
CMA, Ecole des Mines de Paris, BP 207, 06904 Sophia-Antipolis, France
and R.J. Koopmans,
Dow Benelux N.V., Polyolefins & Elastomers R & D, PO Box 48, 4530 AA, Terneuzen,
The Netherlands
Synopsis
The influence of flow rate and die geometry on the observable flow rate / pressure
relationship of a linear High Density Polyethylene is investigated using a capillary
rheometer. The experimental results are applied to an adapted version of the
relaxation-oscillation model proposed by Molenaar and Koopmans for describing the
oscillating flow regime. The current model allows for a quantitative description of the
hysteresis cycle in the oscillating flow regime in terms of the main experimental
variables, such as imposed flow rate, reservoir (barrel) volume and material
compressibility.
a) Present address: P.E.P., 2, Rue P. et M. Curie, 01810, Bellignat (France)
b) To whom correspondence should be addressed
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Rheometry and Detection of Apparent Wall Slip for Poiseuille Flow of
Polymer Solutions and Particulate Dispersions by NMR Velocimetry
Stephen J. Gibbs1†, Kieran L. James1,
Laurance D. Hall1*, Derek E. Haycock2, William J. Frith2,
and Stephen Ablett2
1Herchel Smith Laboratory for Medicinal Chemistry Cambridge University
School of Clinical Medicine University Forvie Site, Robinson Way, Cambridge, CB2 2PZ, UK
2Unilever Research—Colworth House Sharnbrook, Bedfordshire, MK44 1LQ, UK
Synopsis
A flexible and robust approach to nuclear magnetic resonance (NMR) based capillary
rheometry has been developed. The precision of the technique has been explored, with
particular regard to the capability for measurement of apparent wall slip velocities. The
practical implications of alternative NMR rheometry protocols are discussed with regard to
robustness and speed.
NMR rheometry results are presented for a Newtonian fluid (aqueous 50.4% sucrose), a
shear thinning solution (0.2% aqueous xanthan gum), and a particulate system composed of
5-50 micron irregular, soft agar gel particles. In all cases, fully developed Poiseuille
flow was studied in a 4 mm internal diameter, glass capillary. Radial velocity profiles
were measured by NMR velocimetry; radial differentiation provides shear rate values, which
have been scaled by the associated radial positions and measured pressure drops to
determine viscosity as a function of shear rate.
Agreement with cone-and-plate or parallel plate rheometry has been established for each
system. The xanthan solution shows power-law behavior, and no evidence of significant
apparent wall slip. The particulate gel system exhibits power-law behavior, but with
pronounced apparent wall slip. Apparent slip velocities determined by extrapolation of the
NMR velocimetry data to the wall surface and by a Mooney analysis of flow through four
different diameter capillaries agree.
* Author to whom correspondence should be addressed
† Present address: National High Magnetic Field Laboratory - Florida State
University, 1800 E. Paul Dirac Drive, Tallahassee, FL 32306-4005
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Thermodynamic Considerations on the Electro-Rheology of Non-colloidal
Suspensions
Davide A. Hill
Department of Chemical Engineering, University of Notre Dame, du Lac Notre Dame, IN 46556
Synopsis
Thermodynamics provides a convenient framework to analyze the electro-rheology of
suspensions of non-Brownian, non-colloidal particles in Newtonian carriers. Aided by
simple constitutive relations linking suspension architecture to its electrical response,
we examine the evolution of the microstructure upon cessation of flow and the
linear-elastic behavior in the pre-yield region. In the case where the particles and the
fluid are both nonconducting, a rigorous proof can be worked out to show that, upon
cessation of flow, the suspension microstructure will evolve towards a
"pillared" configuration, whereby chains of particles spanning the flow gap are
formed. Also, a maximum in the linear-elastic shear modulus as a function of solid
concentration is predicted in this case, under certain conditions. For finite solid and
carrier conductivities, where Maxwell-Wagner-Sillar polarization can occur, the results
are less rigorous; although some necessary conditions for stability of the pillared
structure can still be inferred.
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The Generalised Engineering Bernoulli Equation [GEBE], and the First
and Second laws of Thermodynamics,
for Viscoelastic Fluids
Gianni Astarita† and Michael E. Mackay‡
Department of Chemical Engineering, University of Delaware, Newark, DE 19716, USA
Synopsis
In this work we thoroughly explore the meanings of dissipation [sometimes referred to
as viscous dissipation] and stress power. To do this we utilize the Cauchy momentum
equations and the first and second laws of thermodynamics. First, the generalized
engineering Bernoulli equation [GEBE] is derived from the Cauchy momentum equations and it
is clearly shown to have nothing to do with a balance of energy. Next, the first law of
thermodynamics or energy balance is discussed and a combined equation by subtracting the
two is derived which we refer to as the mechanoenergy balance [sometimes referred to as
the 'equation of thermal energy']. The fact a difference exists further reinforces the
GEBE is not related to a balance of energy. Finally, the second law of thermodynamics is
presented and the concept of dissipation introduced. An example is presented to
demonstrate the utility of these equations which will hopefully eliminate some confusion
in the literature.
†Permanent address: Department of Materials and Production Engineering,
University of Naples Federico II, Piazzale Tecchio, 80125 Naples, Italy
‡Permanent address: Department of Chemical Engineering, The University of
Queensland, Brisbane 4072, Queensland, Australia
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Out-of-Plane Orientational Dynamics of Polymer Liquid Crystals Under
Flow
N. C. Andrews, A. J. McHugh and B. J. Edwards
Department of Chemical Engineering, University of Illinois, Urbana, IL 61801
Summary
The nonplanar orientational dynamics of polymer liquid crystals (PLC's) is investigated
using a continuum theory based on Hamiltonian mechanics. The initial out-of-plane
orientation is generated through the application of a magnetic field which naturally
appears in the Hamiltonian of the system. Our analysis begins at the instant the magnetic
field is turned off and the flow is started. It is found that the orientational pattern is
varied and rich in transitions. The "kayaking" states and the shear-plane
tumbling states are found to be the dominant attractors for the majority of the parameter
space. Also, this theory has an inbuilt non-affine parameter which is found to have an
important effect on the nature of the final stable orientations.
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Anomalies in the Normal Force Measurement when Using a Force Rebalance
Transducer
Jan M. Niemiec, Jean-Jacques Pesce, and Gregory B. McKenna
Polymers Division, National Institute of Standards and Technology, Gaithersburg, MD 20899
and
Stephen Skocypec and Ronald F. Garritano
Rheometrics, Inc., One Possumtown Road, Piscataway, NJ
Abstract
Torque and normal force measurements in torsional experiments provide a powerful
technique for the efficient measurement of material properties. Over the past several
decades NIST has been active in pioneering the use of such measurements for the
characterization of polymer material behaviors, particularly in transient experiments. In
a recent series of tests using a force rebalance transducer, anomalies in normal force
measurements were observed. It was determined that the active nature of the transducer,
which leads to excellent zero stability, causes thermal heating and consequent expansion
of the system. The transducer length changes are shown to be the cause of the normal force
anomalies and, in collaboration with the equipment manufacturer, suggestions for working
around the problem and potential transducer redesign are discussed.
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Influence of a Nonionic Surfactant on the Rheology of a Hydrophobically
Associating Water Soluble Polymer
Thierry Aubry and Michel Moan
Laboratoire de Rheologie, I. U.P. Genie Mecanique, 6, avenue Victor Le Gorgeu, 29285 Brest
Cedex, France
Synopsis
The rheological behavior of a 1% w/w commercial hydrophobically modified
(hydroxypropyl)guar (HMHPG) in water solution is examined in the presence of a low
molecular weight nonionic surfactant. The linear and nonlinear response to steady and
oscillatory shear flow, at different surfactant concentrations around the cmc, is mainly
compared with the response of a 1% w/w aqueous solution of HMHPG alone, following a
rheological approach previously used by the authors. Below the cmc of the free surfactant
in water, the rheological results show a reinforcement of the reversible associating
network mainly due to an increase of the number of intermolecular hydrophobic
associations, with hardly no modification of the average "strength" of the
hydrophobic junctions. Above the cmc, the rheological data show that there is a
progressive weakening leading to disruption of the intermolecular hydrophobic junction
network. Those results are interpreted in terms of interactions of surfactant molecules
with the regions of intermolecular hydrophobic association.
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On the Stability Of Molecular Weight Distributions As Computed from the
Flow Curves of Polymer Melts
M.R. Nobile, F. Cocchini
Dipartimento di Ingegneria Chimica e Alimentare, Universita' di Salerno, Fisciano (Sa),
Italy
J.V. Lawler
Hoechst Celanese Corporation, Summit, NJ, USA
Abstract
In this work we analyze the possibility to improve the reliability of the conversion
from the viscosity function to the molecular weight distribution (MWD) for linear flexible
polymers. A constrained inverse procedure has been applied to guide the inverse problem to
the correct solution, i.e., an analytical MWD function utilizing the generalized
exponential function (GEX) has been assigned.
The self-consistency of this flow curve - MWD constrained conversion has been tested on
copolyacetal samples of different molecular weights by determining the c2 surface in the
space of the GEX parameters around the minimum. The result is that the constrained inverse
method is capable of yielding meaningful results in terms of MWDs and molecular weight
averages provided that the viscosity data fall into the commonly accepted experimental
error range and cover an adequately wide shear rate range.
Discrepancies between the MWDs calculated from rheological measurements and the
corresponding GPC data have been detected in the case of the polymers of lower molecular
weight. This event probably occurs because of the lack of viscosity data at very high
shear rates due to experimental difficulties. In addition, failure can occur in the
rheological model utilized for the lower molecular weight samples.
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Flow Characteristics of Concentrated Emulsions of Very Viscous Oil in
Water
Gustavo A. Núñez‡, Maria Briceño, Clara Mata,
Hercilio Rivas and Daniel D. Joseph*
Intevep S.A., Los Teques, Venezuela
Abstract
This paper advances ideas and presents experiments on the flow characteristics of
concentrated emulsions of Venezuelan bitumen in water plus surfactant. These emulsions are
studied under a variety of flow conditions, namely between rotating cylinders, in a
colloid mill and in pipes. The ideas advanced here concern the modeling of the highly
viscous bitumen drops as solid spheres and their fracture under contact forces between
neighboring drops, as in comminution, rather than break-up by hydrodynamic forces.
Further, we observe and discuss the local inversion of an emulsion due to local increases
of the bitumen fraction induced by flow and the conditions that lead to slip flow, in
which the drag is reduced by the formation of a lubricating layer of water at the wall. We
believe that the results presented here unveil mechanisms that take place in the pumping
and pipelining of oil-in-water emulsions and therefore contribute to the understanding of
the dynamic stability of these systems.
‡ Corresponding author.
* Department of Aerospace Engineering & Mechanics, University of Minnesota,
Minneapolis, Minnesota, USA, 55455.
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The Effect of Blending Particles with Different Conductivity on
Electrorheological Properties
Ryo Sakurai, Howard See, and Tasuku Saito
Research and Development Division, Bridgestone Corporation, 3-1-1 Ogawahigashi-cho,
Kodaira-shi, Tokyo 187, Japan
Synopsis
We have carried out a set of experiments using anhydrous carbonaceous particles to
determine the effect on the electrorheological properties of blending particles of
different conductivities. We find that there is a significant dip in the shear stress
under an electric field as the concentration of higher conductivity particles is
increased, showing that uniformity of the electrical properties among the particles is a
most important factor in achieving optimum ERF performance. We explain this behavior by a
simple model based on the strength of particle-particle interactions. Measurements of the
dielectric permittivity show that the a parameter of the Cole-Cole expression provides an
excellent way to express the degree of uniformity in the electrical properties. This gives
a convenient method to evaluate the potential performance of an ERF.
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Influence of Amylose Content on the Viscous Behavior of Low Hydrated
Molten Starches
G. della Valle, P. Colonna and A. Patria
INRA, Centre de Recherches Agro-Alimentaires, BP 1627, 44316 NANTES Cedex 03, France
B. Vergnes a)
CEMEF, Ecole des Mines de Paris (URA CNRS 1374) BP 207, 06904 SOPHIA-ANTIPOLIS
Cedex, France
Synopsis
Starches with various amylose contents (0-70 %) were processed on a twin-screw extruder
equipped with a special slit die rheometer. Relationships between thermomechanical
treatment and starch macromolecular degradation are defined, and flow curves are discussed
in order to determine the role of moisture content, product temperature and mechanical
energy on melt viscosity. The viscous behavior is described by a power-law expression.
Viscosity is more sensitive to moisture content and macromolecular degradation at lower
amylose contents. Using multiple regression analysis, expressions for the different
starches are proposed to describe the influence on the viscosity of amylopectin, which is
the macromolecular component with short chain branching. The main differences observed
when decreasing the amylose content are a lower viscosity and less pronounced shear
thinning. These effects are interpreted in terms of entanglements.
a) Corresponding author
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