- A high pressure sliding plate rheometer for polymer melts
- François Koran and John M. Dealy
- Wall slip of polyisobutylene: Interfacial and pressure effects
- François Koran and John M. Dealy
- Melt rheology of poly(lactic acid): Entanglement and chain
architecture effects
- John R. Dorgan, Joshua S. Williams, and David N. Lewis
- Flow profiles of electrorheological suspensions: An
alternative model for ER activity
- S. Henley and F. E. Filisko
- Curvature-driven shear-banding in polymer melts
- J. L. Goveas and G. H. Fredrickson
- Fluctuations and self-diffusion of sheared granular material
flows
- Shu-San Hsiau and Yuh-Min Shieh
- Influence of the chemical nature of various geometries on
the rheological behavior of a lamellar lyotropic phase
- N. Jager-Lézer, J. L. Grossiord, Y. Feutelais, J. Doucet, J. F. Tranchant, V. Alard,
and A. Baszkin
- Associative polymers bearing n-allyl hydrophobes: Rheological
evidence for microgel-like behavior
- Robert J. English, Srinivasa R. Raghavan, Richard D. Jenkins, and Saad A. Khan
- Dynamic inflation of hyperelastic spherical membranes
- E. Verron, R. E. Khayat, A. Derdouri, and B. Peseux
- Particle migration in tube flow of suspension
- Minsoo Han, Chongyoup Kim, Minchul Kim, and Soonchil Lee
- A continuum approach to electrorheology
- Yuri M. Shkel and Daniel J. Klingenberg
- Pressure and temperature effects in slit rheometry
- Grant Hay, K. M. Awati, Y. Park, and M. E. Mackay
- The Considère condition and rapid stretching of linear and
branched polymer melts
- Gareth H. McKinley and Ole Hassager
- Curvilinear flows of noncolloidal suspensions: The role of
normal stresses
- Jeffrey F. Morris and Fabienne Boulay
- Simulation of the Doi-Edwards model in complex flow
- A. P. G. van Heel, M. A. Hulsen, and B. H. A. A. van den Brule
- Rheological behavior and stability of concentrated silica
suspensions stabilized with g-methacryloxypropyl triethoxy silane
- Jae-Dong Lee, Jae-Hyun So, and Seung-Man Yang
A high pressure
sliding plate rheometer for polymer melts
François Koran1 and John M. Dealy*
Department of Chemical Engineering
McGill University, Canada
1 Present address: Solutia, Springfield, MA, USA
*Corresponding Author: john@chemeng.lan.mcgill.ca
Abstract
A high-pressure sliding plate rheometer has been
developed to investigate the effect of pressure on the rheological behavior of molten
polymers and elastomers. The new rheometer operates at pressures up to 70 MPa and
temperatures up to 225°C. The sample is subjected to simple
shear, and the resulting shear stress is measured locally using a shear stress transducer.
This design eliminates the inhomogeneities in pressure and shear rate that occur in high
pressure capillary and slit rheometers. Preliminary evaluation of the new instrument was
carried out using a linear low density polyethylene. Viscosity curves were generated at
pressures ranging from atmospheric pressure to 70 MPa, and the pressure coefficient of
viscosity was determined. Experiments were also carried out in step strain and large
amplitude oscillatory shear, demonstrating the new rheometer's use to study the nonlinear
viscoelastic behavior of molten polymers. Finally, this instrument was used to study
strain-induced crystallization.
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François Koran1 and John M. Dealy*
Department of Chemical Engineering
McGill University, Canada
1 Present address: Solutia,
Springfield, MA, USA
*Corresponding Author: john@chemeng.lan.mcgill.ca
Abstract
A high-pressure sliding plate rheometer was used to investigate the flow behavior of
polyisobutylene in simple shear. Experiments carried out using smooth steel surfaces
revealed that wall slip is a dominant feature of the flow at the pressures, temperatures
and rates of deformation typically found in the processing of elastomers. A set of grooved
plates made it possible to obtain viscosity data at stresses up to 20 kPa, but at higher
stresses, the sample "slipped" even on the grooved plates. These data were
fitted to a Cross viscosity model and extrapolated in order to estimate the viscosity at
higher stresses. Flow curves (shear stress versus nominal shear rate) generated using
fluoroelastomer-steel and steel-steel pairs of plates exhibited four distinct flow
regimes: no-slip, adhesive slip, mixed adhesive and cohesive slip, and primarily cohesive
slip. Slip velocities were calculated by comparing the no-slip stresses estimated using
the Cross model with measured values. The effect of pressure on cohesive wall slip was
found to scale with pressure in the same way as viscosity, while the effect of pressure on
adhesive wall slip did not.
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John R. Dorgan* and Joshua S. Williams
Department of Chemical Engineering
Colorado School of Mines, Golden, CO 80401 USA
David N. Lewis
Chronopol Inc., 4545 Mclntyre Street
Golden, CO 80403 USA
*Corresponding Author: jdorgan@mines.edu
Abstract
Poly(lactic acids) (PLAs) are a family of polyesters available via fermentation from
renewable resources and are the subject of considerable recent commercial attention. In
this study, the melt rheological properties of a family of poly(lactic acid) stars are
investigated and compared to the properties of the linear material. For polymers made from
a 98:2 ratio of the L to D enantiomeric monomers it is found that the entanglement
molecular weight is in the range of nine thousand grams per mole (Me » 8,700 g/mol) while the molecular weight for branch entanglement is
inferred to be approximately thirty-five thousand grams per mole (Mb » 34,600 g/mol). In addition, the zero shear viscosity of the linear
material increases with the 4.6 power of molecular weight. These results may suggest that
PLA is a semi-stiff polymer in accordance with other recent findings. The increase in zero
shear viscosity for the branched materials is measured and quantified in terms of
appropriate enhancement factors. Relaxation spectra show that the transition zone for the
linear and branched materials are nearly indistinguishable while the star polymers have
greater contributions to the terminal regime. The effects of chain architecture on the
flow activation are found to be modest implying that small scale motions in PLA
homopolymers largely control this phenomenon. Good agreement is found between the dynamic
data and many aspects of the theory of star polymers, however, a dependence of the zero
shear viscosity on the number of arms is observed.
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S. Henley and F. E. Filisko
Departments of Materials Science and Engineering
and Macromolecular Science and Engineering
The University of Michigan, Ann Arbor, Michigan 48109-2136 USA
Abstract
This paper shows the effect of the coupling of an electric field with a shear field on
a suspension of polarizeable or ER active particles. It demonstrates that the elementary
particles in an electrorheologically active suspension, when the suspension is under flow
and simultaneously under the influence of a large electric field, organize into tight
packed lamellar formations, the type and orientation being related to the shear field or
type of device imposing the shear field. These formations resemble walls between parallel
plates, cylinders between parallel discs, and discs between concentric cylinders. In all
cases the columns making up these formations are oriented in the field direction. When
exposed to a field but not under flow, the particles assemble together into numerous
columnar like clusters of similar diameter (100- 200 mm), which
are uniformly but randomly distributed between the electrodes and oriented in the field
direction. Flow alone in the absence of an electric field produces no segregation of the
elementary particles in the suspension. An alternative model for the electrorheological
phenomenon is proposed.
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J. L. Goveas1 and G. H. Fredrickson2
1 Department of Chemical Engineering MS-362
Rice University, 6100 Main Street, Houston, TX 77025 USA
2 Department of Chemical Engineering
University of California, Santa Barbara, CA 93106 USA
Abstract
We consider a melt of two chemically identical homopolymers of different lengths. Both
species obey Rouse dynamics, and always form a homogeneous mixture at equilibrium. Under
shear flow in a wide-gap Couette, such a system exhibits strongly inhomogeneous
steady-states, which resemble macro-phase separated blends. The corresponding velocity
profile is non-monotonic and exhibits distinct shear bands. These findings may have
implications for the processing of polydisperse polymer melts.
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Shu-San Hsiau* and Yuh-Min Shieh
Department of Mechanical Engineering, National Central University
Taiwan 32054, Republic of China
*Corresponding Author: sshsiau@cc.ncu.edu.tw
Abstract
Experiments were performed in a shear cell device with adjustable lower wall velocity.
The glass spheres with a mean diameter of 3 mm were used as granular materials. Image
processing technology and particle tracking method were employed to measure the average
and fluctuation velocities in the streamwise and the transverse directions. Because of
gravitation force, the flows consist of both a solid-like region with higher and more
uniform velocities in the lower test section and a fluid-like region in the upper part.
The velocity fluctuations were anisotropic and were greater in the streamwise direction.
By tracking the movements of particles continually, the variation in the mean-square
diffusive displacements with time was plotted and the self-diffusion coefficient was
determined. The self-diffusion coefficients in the streamwise direction were much higher
than those in the transverse direction. The dependence of the diffusion coefficients on
the velocity fluctuations and the shear rate were discussed.
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Influence of the chemical nature of various
geometries on the rheological behavior of a lamellar lyotropic phase
N. Jager-Lézer and J. L. Grossiord*
Laboratoire de Physique Pharmaceutique, Faculté de Pharmacie de Paris XI
5 rue Jean-Baptiste Clément, 92296 Châtenay-Malabry, France
Y. Feutelais
Laboratoire de Chimie Minérale, Faculté de Pharmacie de Paris XI
5 rue Jean-Baptiste Clément, 92296 Châtenay-Malabry, France
J. Doucet
Laboratoire pour l'Utilisation du Rayonnement Electromagnétique (LURE)
Centre Universitaire Paris-Sud, Bâtiment 209D, 91405 Orsay Cedex, France
J. F. Tranchant and V. Alard
Laboratoire de Physico-Chimie, Parfums Christian Dior
1 rue d'Enfer, 45804 Saint Jean-de-Braye, France
A. Baszkin
Laboratoire de Physico-Chimie des Surfaces, URA CNRS 1218
Faculté de Pharmacie de Paris XI, 5 rue Jean-Baptiste Clément
92296 Châtenay-Malabry, France
*Corresponding Author: jean-louis.grossiord@phypha.u-psud.fr
Abstract
The influence of the chemical nature of the substrate was studied in order to determine
its impact on the rheological behavior of lyotropic lamellar phases. Small-angle X-ray
diffraction analysis established that the plastic behavior of the samples could be
explained by a large disorganization of the lamellar layers in the vicinity of surfaces as
stainless steel, gold, tin, copper, and bismuth. On the contrary, layers alignment was
almost perfect on quartz and lamellar samples displayed a dominant viscous behavior
induced by the flow of the lamellar layers in vicinity of the surfaces. On zinc sulphide,
a halfway behavior was observed and the lamellar sample showed two yield stress: one is
necessary to induce local alignment of layers in the vicinity of the surfaces, the other
must align the layers of the lamellar sandwich in the flow direction. Assumptions on the
origin of the complex and varied organization have been studied by considering the surface
free energy and the surface topology. However, no obvious relationship could be
established between surface free energy and liquid crystal alignment. Similarly, no
influence of the topology on lamellar orientation could be brought to the fore.
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Robert J. English1, Srinivasa R. Raghavan2,
Richard D. Jenkins3, and Saad A. Khan2*
1 Department of Color Chemistry
The University of Leeds, Leeds, LS2 9JT, UK
2 Department of Chemical Engineering
North Carolina State University, Raleigh, NC 27695-7905, USA
3 Union Carbide Asia Pacific Inc., Technical Center
16 Science Park Drive, The Pasteur, Singapore 118227
* Corresponding Author: khan@eos.ncsu.edu
Phone: (919) 515-4519; Fax: (919) 515-3465
Abstract
Rheological techniques are used to probe the behavior of hydrophobic alkali-swellable
emulsion (HASE) polymers, bearing n-alkyl hydrophobes, in aqueous-alkaline media. The
polymers possess a comb-like architecture with a polyelectrolyte backbone (ethyl acrylate-co-methacrylic
acid) and hydrophobes (ca. 16 per polymer chain) tethered to the backbone via
polyether side chains. The size of the hydrophobes is varied from n-C8
to n-C20 in this study. It is shown that, at such a level of hydrophobic
modification, and at relatively high polymer concentrations, the microstructure in these
polymer systems is akin to that existing in concentrated microgels. Thus, the original
polymer latex particles swell extensively in alkaline media and disintegrate to form a
system of close-packed, compressible ("soft") aggregates. This is reflected in
the rheological response of the system where we observe a high steady shear viscosity with
no zero-shear plateau at low shear rates followed by considerable shear-thinning, and, a
characteristic power-law behavior (G', G" ~ w0.4)
under oscillatory shear persisting over a broad range of time scales.
Concentration-independent master curves are obtained for the storage modulus, G', with the
level of G' increasing with hydrophobe size. The similarity in the dynamic response
suggests that there exists a qualitative equivalence in microstructure over the range of
systems, the only difference being the "softness" or compressibility of the
particles. Data from this study are also contrasted with those for a similar HASE polymer
bearing a smaller number of alkylaryl hydrophobes [English et al. (1997)]. In the
latter case, the rheology can be interpreted in terms of hydrophobic associations and
chain entanglements occurring in solution. Thus, subtle variations in molecular
architecture are shown to cause significant differences in morphology and microstructure
for these polymer systems.
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Dynamic inflation of hyperelastic spherical
membranes
E. Verron1, R. E. Khayat2*, A. Derdouri3,
and B. Peseux1
1 Laboratoire de Mécanique et Matériaux, Division Structures
Ecole Centrale de Nantes, B.P. 92101, 44321 Nantes Cedex 3, France
2 Department of Mechanical and Materials Engineering
The University of Western Ontario, London, Ontario, Canada N6A 5B9
3 Industrial Materials Institute, National Research Council
of Canada
75 De Mortagne Blvd, Boucherville, Québec, Canada J4B 6Y4
*Corresponding Author
Abstract
The dynamic inflation of a hyperelastic spherical
membranes of a Mooney-Rivlin material is analyzed in this study. Various inflation regimes
are identified through ranges of the material parameters and driving pressure. In
particular, the conditions for oscillatory inflation around the static fixed point are
examined. It is found that, for a given material, the frequency of oscillation exhibits a
maximum at some pressure level, which tends to increase for materials closer to
neo-Hookean behavior.
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Minsoo Han, Chongyoup Kim*
Department of Polymer Engineering, Chungnam National University
220 Goong-dong, Yoosong-goo, Taejeon 305-764, Korea
Minchul Kim and Soonchil Lee
Department of Physics, Korea Advanced Institute of Science and Technology
373-1 Gusong-dong, Yoosong-goo, Taejeon 305-701, Korea
* Corresponding author
Abstract
In this research, we investigated the migration of particles in the tube flow of
suspension for a wide range of particle loading (f0)
and particle Reynolds number (Rep), using a magnetic resonance
imaging (MRI) technique. The suspension consisted of nearly monodisperse
polymethylmethacrylate spheres in a density matched Newtonian fluid. The volume fraction
of the solid was 0.06 - 0.40. Both the velocity and the concentration distributions were
measured under fully developed conditions. It has been found that, when f0 was small (£ 0.1) and Rep
was not small (> »0.2), the particles moved toward the
position at a distance of 0.5 - 0.6 R (tube radius) from the tube axis and the
velocity profile was parabolic. When f0 = 0.4,
particles always moved toward the center of tube and the velocity profile was blunted. The
degree of blunting was larger for smaller Rep. Between these two
limiting cases, the particle migration was dependent on Rep . When Rep
is small the particles move toward the tube axis regardless of f0.
When f0 is 0.2 - 0.3 and Rep > »0.2, particles are concentrated both at the center and at the
middle of the tube axis and tube wall. The velocity profile keeps the parabolic form
unless the particles are concentrated regardless of Rep. Apparent wall
slip is not observed except for the case of f0 =
0.40. It is suggested that, when the particle Reynolds number is larger than 0.1, the
inertial effect cannot be neglected regardless of the average particle concentration.
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Yuri M. Shkel and Daniel J. Klingenberg
Department of Chemical Engineering and Rheology Research Center
University of Wisconsin
1415 Engineering Drive, Madison, WI 53706 USA
Abstract
An equilibrium thermodynamic approach is employed to derive a continuum-level
expression for the electric field-induced stress in uniaxial anisotropic materials.
Although this model is developed specifically to describe electrorheological and
electrostrictive behavior of suspensions, it also applies to other uniaxial materials such
as nonpolar nematic liquid crystals, biaxially oriented polymer films, and paper. This
model introduces new electrostriction coefficients, which are material parameters that
describe the strain dependence of the dielectric tensor as well as the field-induced
stresses. An experimental technique for measuring the electrostriction parameters is
outlined. An idealized microscopic model is presented to illustrate the relationships
between microscopic parameters and the macroscopic electrostriction coefficients. The
model is used to determine the stresses in common applications; predictions from the
continuum approach agree with direct calculations from a microscopic approach of the
normal stress and static shear modulus of electrorheological suspensions.
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Grant Hay1,2, K. M. Awati1, Y. Park1,
and M. E. Mackay1,2*
1 Materials Characterisation and Processing Centre
2 The Cooperative Research Centre
for International Food Manufacture and Packaging Science
Department of Chemical Engineering
The University of Queensland, Qld. 4072, Australia
* Corresponding author. Present address:
Department of Chemical, Biochemical and Materials Engineering
Stevens Institute of Technology, Hoboken 07030, NJ, USA
e-mail: mmackay@stevens-tech.edu
Abstract
We present an approximate theoretical treatment of pressure and viscous heating effects
on the flow of a power law fluid through a slit die. It is assumed that the flow remains
one dimensional, and the accuracy of this approximation is checked via finite element
simulations of the complete momentum and energy equations. For pressures typically
achieved in the laboratory it is seen that the one dimensional approximation compares well
with the simulations. The model therefore offers a method of including pressure and
viscous heating effects in the analysis of experiments and is used to rationalise
experimentally obtained pressure profiles for the flow of polymer melts through a slit
die. Data for the flow of a linear low density polyethylene and a polystyrene melt in a
slit die show these two effects are significant under normal laboratory conditions. Thus,
the shear stress - shear rate curves will be affected to the point of being inaccurate at
high shear rates. In addition, it is found that the typical technique to correct for a
pressure dependent viscosity is also inaccurate being affected by the viscous heating and
heat transfer from the melt to the die.
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Gareth H. McKinley
Department of Mechanical Engineering
Massachusetts Institute of Technology
Cambridge, MA 02139, USA
Ole Hassager
Polymer Centre DTU
Department of Chemical Engineering
Technical University of Denmark
DK2800 Lyngby, Denmark
Abstract
We analyze the onset of 'necking' and subsequent filament failure during the transient
uniaxial elongation of viscoelastic fluid samples in extensional rheometers. In the limit
of rapid elongation (such that no molecular relaxation occurs) the external work applied
is all stored elastically and the Considère criterion originally developed in solid
mechanics can be used to quantitatively predict the critical Hencky strain to failure. By
comparing the predictions of the Doi-Edwards model for linear homopolymer melts with those
of the 'Pom-Pom' model recently proposed by McLeish and Larson (J. Rheol. 42,
(1998) p. 81-110) for prototypical branched melts we show that the critical strain to
failure in rapid elongation of a rubbery material is intimately linked to the molecular
topology of the chain, especially the degree of chain branching. The onset of necking
instability is monotonically shifted to larger Hencky strains as the number of branches is
increased. Numerical computations at finite Deborah numbers also show that there is an
optimal range of deformation rates over which homogeneous extensions can be maintained to
large strain.
We also consider other rapid homogeneous stretching deformations, such as biaxial and
planar stretching, and show that the degree of stabilization afforded by inclusion of
material with long-chain branching is a sensitive function of the imposed mode of
deformation.
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Jeffrey F. Morris* and Fabienne Boulay1
School of Chemical Engineering
Georgia Institute of Technology
Atlanta, GA 30332-0100 USA
1 Present address: 5, rue Henri-Duchene 75015, Paris, France
* E-mail: jeff.morris@che.gatech.edu
Abstract
The role of normal stresses in causing particle migration and macroscopic spatial
variation of the particle volume fraction, f, in a
mixture of rigid neutrally-buoyant spherical particles suspended in Newtonian fluid is
examined for curvilinear shear flows. The problem is studied for monodisperse noncolloidal
Stokes-flow suspensions, i.e. for conditions of low-Reynolds-number flow and
infinite Péclet number, Pe = O(h g-dot a3/kT),
where h is the suspending fluid viscosity, g-dot is the shear rate, a is the particle radius, and kT
is the thermal energy. Wide-gap Couette, parallel-plate torsional, and cone-and-plate
torsional flows are studied.
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A. P. G. van Heel, M. A. Hulsen, and B. H. A. A. van den Brule
J. M. Burgers Centre for Fluid Mechanics, Delft University of Technology
Rotterdamseweg 145, 2628 AL Delft, The Netherlands
Abstract
The Doi-Edwards model is simulated in start-up of two-dimensional complex flow. The
flow geometry is that of a cylinder confined between two parallel plates. Two different,
new simulation methods are used. The first is based on the configuration field approach.
The second method is a new method which is introduced in this paper. We refer to this
approach as the deformation field method. Theoretically the methods are equivalent. It
will be shown that the deformation field approach is very efficient. Furthermore, the
method opens possibilities to study extensions of the Doi-Edwards model which include
tube-stretch and convected constraint release.
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Rheological behavior and stability of concentrated
silica suspensions stabilized with g-methacryloxypropyl triethoxy silane
Jae-Dong Lee, Jae-Hyun So, and Seung-Man Yang*
Department of Chemical Engineering
Korea Advanced Institute of Science and Technology
373-1, Kusong-dong, Yusong-gu
Taejon 305-701, Korea
*Corresponding Author: smyang@cais.kaist.ac.kr
Telephone: 82-42-869-3922; Fax: 82-42-869-3910
Abstract
In the present paper, the rheological behavior and phase stability of concentrated
silica suspensions were investigated experimentally by examining the effects of particle
size and temperature. The silica particles were stabilized by adsorption of a silane
coupling agent, g-methacryloxypropyl triethoxy silane (MPTES).
The MPTES-coated silica particles behaved like hard spheres and exhibited the dispersion
stability in tetrahydrofurfuryl alcohol (THFFA), which was used as a refractive-index
matching solvent. For a monodisperse suspension, the limiting viscosities at high shear
rates were correlated satisfactorily with the Krieger-Dougherty equation until the
particle volume fraction (f) reached 0.45 above which
the limiting high-shear-rate viscosities did not exist. The highly concentrated
monodisperse suspensions above f =0.50 displayed the
rapidly shear thinning viscosity at low shear rates and underwent the shear thickening at
high shear rates. Specifically, the onset of shear thickening shifted to a higher shear
rate either as temperature rose or as the suspension became stable. The dichroism from
light passed in the flow-gradient direction probed the most effectively the order-disorder
transition such as disappearance of hexagonally ordered layered structure and formation of
particle clustering, which caused shear thickening at high shear rates. The abrupt change
in dichroism caused by the breakdown of hexagonally layered structure occurred almost one
decade before the onset of shear thickening. Finally, the bimodal suspensions prepared
here possessed the reduced shear viscosity and stress in comparison with the monodisperse
suspensions of identical volume fraction. Degree of the viscosity reduction became
conspicuous for concentrated suspensions usually above f
=0.40.
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