- A geometrical interpretation of large amplitude
oscillatory shear response
- Kwang Soo Cho, Kyu Hyun, Kyung Hyun Ahn, and Seung Jong Lee
- “Fifty-cent rheometer” for yield stress
measurements : From slump to spreading flow
- N. Roussel and P. Coussot
- Melt rheology of variable L-content poly(lactic
acid)
- John R. Dorgan, Jay Janzen, Michael P. Clayton, Sukhendu B. Hait, and
Daniel M. Knauss
- Viscometric investigation of aggregate formation in
dilute conjugated polymer solutions
- Chi C. Hua, Chien L. Chen, Chi W. Chang, Cheng K. Lee, and Show A.
Chen
- Apparent slip and viscoplasticity of concentrated
suspensions
- Dilhan M. Kalyon
- Measuring the transient extensional rheology of
polyethylene melts using the SER Universal Testing Platform
- Martin Sentmanat, Benjamin N. Wang, and Gareth H. McKinley
- Study of the stick-slip phenomenon of linear
low-density polyethylene in a brass die by using electrical measurements
- José Pérez-González
- Simulation of fiber spinning including flow
induced crystallization
- K. Kannan and K. R. Rajagopal
- Orientation and rupture of fractal colloidal gels
during start-up of steady shear flow
- Ali Mohraz and Michael J. Solomon
- The effect of block copolymer architecture on
the coalescence and interfacial elasticity in compatibilized polymer
blends
- Ellen Van Hemelrijck, Peter Van Puyvelde, Christopher W. Macosko, and
Paula Moldenaers
- The rheology and microstructure of acicular
precipitated calcium carbonate colloidal suspensions through the shear
thickening transition
- Ronald G. Egres and Norman J. Wagner
- Rheology and phase behavior of copolymer-templated
nanocomposite materials
- Danilo C. Pozzo, Kate R. Hollabaugh and Lynn M. Walker
Kwang Soo Cho
Department of Polymer Science, College of Engineering
Kyungpook National University
Sangyeok-Dong 1370, Daegu, Korea, 702-701
Kyu Hyun, Kyung Hyun Ahn a), and Seung Jong Lee
School of Chemical Engineering
Seoul National University
Seoul, Korea, 151-744
Abstract
Although the stress of oscillatory shear flow can be decomposed into
elastic and viscous parts in the linear regime, it is not yet known how
to decompose the stress of a large amplitude oscillatory shear (LAOS)
flow. We developed a method of analyzing LAOS data, which decomposes the
stress into elastic and viscous components on the basis of a sound
mathematical and physical foundation. This method is based on the
symmetry of the stress and is a generalization of linear viscoelasticity
from the viewpoint of geometry. The proposed method is more powerful
than previous methods such as Fourier transform analysis and the
Lissajous plot, in that it is more sensitive to the presence of
nonlinearities and it is easier to determine nonlinear parameters.
a) Corresponding Author:
ahnnet@snu.ac.kr
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N. Roussel a,c) and
P. Coussot b)
a) Division Bétons et
Composites Cimentaires
Laboratoire des Ponts et Chaussées, 75015 Paris, France
b) Laboratoire des
Matériaux et des Structures du Génie Civil
Institut Navier, 77420 Champs sur Marne, France
Abstract
The slump test, originally used to determine the « workability » of
fresh concrete, has since been used in many industrial fields (mining
industry, food industry.). It offers a quick and easy way to measure the
yield stress of suspensions or pasty materials. The model used for
estimating the yield stress from the measured conical slump was first
written by Murata (1984), corrected by Christensen (1991) and adapted
for a cylindrical geometry by Pashias (1996). However, a discrepancy
between experimental and predicted slumps still appears in the case of
conical slumps (Clayton (2003)) and for high yield stress materials. In
the present paper, we extend the theoretical analysis of this simple
practical test by including different flow regimes according to the
ratio between the radius (R) and the height (H) of the
slumped cone. We propose analytical solutions of the flow for two
asymptotic regimes, namely H >> R and H << R.
We finally compare the predictions of these solutions in terms of yield
stress and previous expressions to three-dimensional numerical
simulations and experimental data on a large range of yield stresses.
This makes it possible to clarify the field of validity of the different
approaches and provide further practical tools for estimating the yield
stress of coarse materials.
c)
Corresponding author:
nicolas.roussel@lcpc.fr
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John R. Dorgan a), Jay Janzen, Michael P.
Clayton b), Sukhendu B. Hait c), and Daniel M.
Knauss c)
Chemical Engineering Department and Department of
Chemistry and Geochemistry
Colorado School of Mines, Golden, Colorado 80401
Abstract
Polylactides (PLAs) have been known for several decades and have
recently gained considerable commercial significance. This development
makes it highly desirable to have the rheological properties of these
materials well characterized and reduced to useable mathematical models.
However, comprehensive rheological characterization of PLAs is not yet
available from the literature. In this study, rheological and thermal
measurements were made on a comprehensive and well-characterized set of
homopolymers and copolymers spanning wide ranges of molecular mass and
stereoisomer proportions (L-content). For all compositions within the
weight average molecular weight range of 105 to 106
(g/mol) and a reference temperature of 180ºC, the zero shear viscosity
is described by the relationship log(h0)
= 14.26 + 3.4 log(Mw), the plateau modulus is 1.0 ±
0.2 MPa, and average WLF parameters are c1=3.24 1/K
and c2=164.9 K; the later correspond to a Vogel
temperature of 288.25 K. The values of the glass transition temperatures
at infinite molecular weight for 100, 80, and 50% L-content are 60.2°C,
56.4°C, and 54.6°C, respectively. Based upon a chain packing model,
molecular parameters determined include a packing length of 2.51 Å, a
tube diameter of 47.7 Å, and a characteristic ratio of 6.5 ± 0.9,
independent of stereoisomeric composition. The critical molecular weight
for entanglement, Mc, is found to be near 9000 g/mol
while the molecular weight between entanglements, Me,
is near 4000 g/mol. Reasons for accepting these values over previous
literature studies are given; the available data imply linear
polylactides are typical glass-forming polymers.
a) Author for correspondence. e-mail:
jdorgan@mines.edu
b) Present affiliation: Dept. of Chemical Engineering, Univ. of
Queensland, Australia
c) Dept. of Chemistry and Geochemistry.
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Chi C. Hua, Chien L. Chen, Chi W. Chang, and Cheng K.
Lee
Department of Chemical Engineering
National Chung Cheng University
Chia-Yi 621, Taiwan, R.O.C.
Show A. Chen
Department of Chemical Engineering
National Tsing Hua University
Hsin-Chu 30013, Taiwan, R.O.C.
Abstract
We perform systematical viscometric investigations on the dilute
solutions of a model electroluminescent conjugated polymer,
poly(2-methoxy-5-(2’-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV).
Results on low-shear viscosity measurement reveal markedly close
correspondence between viscometric and aggregation properties. Peculiar
viscometric features of MEH-PPV solutions include (1) the polymer
contribution to the solution viscosity exhibits a slow yet persistent
decrease during constant-temperature aging, and (2) the same quantity
exhibits thermal irreversibility as the solution has been subjected to a
short-term thermal treatment. These viscometric features and
corresponding aggregation properties are bridged using
kinetic-theory/thermodynamic arguments and molecular dynamics (MD)
simulations. Primary implications as to the effects of the choice of
solvent, solvent quality, concentration, aging, and short-term thermal
treatment on the aggregation properties agree fairly well with recent
optical observations. Overall, the present study suggests that
rheological characterizations may be very useful for gaining additional
insights into the aggregation properties for conjugated polymer
solutions.
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Dilhan M. Kalyon a)
Stevens Institute of Technology
Castle Point Station, Hoboken, NJ 07030
Abstract
The apparent slip flows of incompressible and viscoplastic (Herschel-Bulkley)
fluid in plane Couette, capillary and rectangular slit dies under
fully-developed, isothermal and creeping flow conditions were analyzed
assuming that the apparent slip layer consists solely of the binder and
its thickness is independent of the flow rate. Both the draginduced
(plane Couette) and pressure-induced (capillary and slit) flows generate
the same dependencies of the wall-slip velocity on the wall shear
stress. Navier´s slip coefficient, which relates the wall-slip velocity
to the shear stress, is similar for all three flows and is a function of
the thickness of the apparent slip layer and the shear viscosity of the
binder. The assumed apparent slip mechanism provides methodologies for
the determination of the slip velocity values that are consistent with
the traditional Mooney method and furthermore allows the determination
of the true shear rate of the suspension at the wall and the yield
stress. The analysis of the slip data of various concentrated
suspensions of rigid particles reveals that as a first approximation the
apparent slip layer thickness is related to the particle diameter and
the ratio of the volume loading level over the maximum packing fraction
of the particles.
a) E-mail:
dkalyon@stevens.edu
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Martin Sentmanat
Senkhar Technologies, LLC
Akron, OH
Benjamin N. Wang
Institute for Soldier Nanotechnology and Department of Chemical Engineering
Massachusetts Institute of Technology
Cambridge, MA 02139
Gareth H. McKinley
Hatsopoulos Microfluids Laboratory and Institute for Soldier Nanotechnology
Department of Mechanical Engineering
Massachusetts Institute of Technology
Cambridge, MA 02139
Abstract
We use a new extensional rheology test fixture that has been developed
for conventional torsional rheometers to measure the transient
extensional stress growth in a number of different molten polyethylene
samples including a linear low density polyethylene (Dow Affinity PL
1880), a low density polyethylene (Lupolen 1840H) and an ultrahigh
molecular weight polyethylene (UHMWPE). The transient uniaxial
extensional viscosity functions for the LLDPE and LDPE samples have both
been reported previously in the literature using well-established
instruments and this allows us to benchmark the performance of the new
test fixture. Transient stress growth experiments are carried out over a
range of Hencky strain rates from 0.003 s-1 to 30 s-1
and the data shows excellent agreement with the published material
functions. At deformation rates greater than 0.3 s-1 a true
steady state extensional viscosity is not obtained in the LDPE samples
due to the onset of necking failure in the elongating strips of polymer;
however the limiting values of the transient extensional viscosity at
the onset of sample failure agree well with previously published values
for the steady state extensional viscosity. This apparent steady-state
extensional viscosity first increases with deformation rate before
ultimately decreasing as approximately e-dot−0.5.
In addition we perform extensional step-strain measurements at small
Hencky strains and demonstrate good agreement with the relaxation
modulus obtained from shear rheometry. Extensional creep measurements
are performed over a range of constant imposed tensile stresses and also
agree well with the measured shear creep compliance. Finally, tensile
stress relaxation experiments are carried out after a range of imposed
Hencky strains. These tests demonstrate that following large extensional
deformations the tensile stresses relax nonlinearly and also that,
beyond a critical strain, the material is unstable to viscoelastic
necking and rupture. Additional transient extensional stress growth
measurements using highly entangled linear UHMWPE samples show greatly
reduced strains to failure, that are in agreement with the predictions
of the Considère theory.
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José Pérez-González a)
Laboratorio de Reología, Escuela Superior de Física y
Matemáticas
Instituto Politécnico Nacional
Apdo. Postal 118-209, C. P. 07051, México, D. F., Mexico
Abstract
Extrusion through brass dies
has been found to be useful to eliminate sharkskin and stick-slip
instabilities in linear low-density polyethylene. However, the
physicochemical interaction of polyethylene melts with brass dies is not
well understood. In the present work, such an interaction is analyzed by
using electrical measurements. Experiments were performed in a single
screw extruder at a temperature of 190 °C with a metallocene linear
low-density polyethylene and a brass die. The interaction between the
polymer melt and the die changed with time. Different flow curves were
obtained as the extrusion time was increased, up to reach an invariant
flow curve. An irreversible transition from slip to no-slip at the die
wall under stable flow was observed consistent with a change in the sign
of the measured electric charge. The critical shear stress for the onset
of the stick-slip also increased with the extrusion time. Electrical
measurements reproduced with fidelity the stick-slip dynamics. Pressure
oscillations were accompanied by in-phase variations of electrical
charge during the stick-slip, from which a cohesive failure is suggested
for slip in this flow regime. For long extrusion times, a new phenomenon
was observed, which is the disappearance of pressure and electric charge
oscillations, but in the presence of a non-monotonic flow curve. It is
suggested that the density of adsorbed chains at the wall increases with
time because of contamination of the die wall, ending in a “dry brush”
regime that suppresses pressure oscillations and produces a true plateau
in the flow curve.
a)
E-mail:
jpg@esfm.ipn.mx
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K. Kannan and K. R. Rajagopal a)
Department of Mechanical Engineering
Texas A&M University, College Station, TX 77843
Abstract
Kannan et al. (2002) studied the problem of fiber spinning, for
polymers that are largely atactic in nature, within a thermodynamic
framework developed by Rao and Rajagopal (2002), where significant
crystallization does not take place. Here, we develop a model within the
same framework that can take into account flow-induced crystallization
and the anisotropy of the crystalline part of the semicrystalline
polymer. We find that the predictions of the model agree very well with
experimental data.
a) Author to whom correspondence should be
addressed. Email:
krajagopal@mengr.tamu.edu
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Ali Mohraz and Michael J. Solomon
Department of Chemical Engineering
University of Michigan
Ann Arbor, MI 48109-2136
Abstract
The transient structural evolution of polystyrene colloidal gels with
fractal structure is quantified during start-up of steady shear flow by
time-resolved small-angle light scattering (SALS) and rheometry. Three
distinct regimes are identified in the velocity-gradient plane:
structural orientation, network break-up and cluster densification.
Structural anisotropy in the first regime is a universal function of
applied strain. Flow cessation in this regime shows a lack of structural
relaxation for Pe << 1, where Pe is the Peclet number. In
the second regime, the anisotropy attains a maximum value before
monotonically decreasing. The volume fraction dependence of the critical
strain for maximum anisotropy follows the scaling: 1 + 0.6gc,r
~ f (1-x)/(3-D).
Here x and D are the backbone and cluster fractal
dimensions, respectively. This scaling agrees with the simple model of a
gel network that ruptures after the cluster backbone is extended
affinely to its full length. Rheological measurements demonstrate that
the maximum anisotropy coincides with a maximum in shear stress.
Qualitative differences between the transient anisotropy of fractal gels
comprised of spheres and rods support the conclusion that the
microstructural origin of the anisotropy maximum in sphere aggregates is
the free rotation of singly connected regions of the gel backbone.
Return to top.
Ellen Van Hemelrijck a), Peter Van Puyvelde
a,c), Christopher W. Macosko b), and Paula Moldenaers
a)
a) K.U. Leuven, Department of Chemical Engineering
W. de Croylaan 46, B-3001 Leuven, Belgium
b) Department of Chemical Engineering and Materials
Science
University of Minnesota, Minneapolis, MN 55455, U.S.A.
Abstract
The effect of block copolymer
architecture on the suppression of droplet coalescence and on the
interfacial elasticity was studied in immiscible blends of
polydimethylsiloxane (PDMS) and polyisoprene (PI) with a droplet-matrix
morphology. The PDMS-PI diblock copolymers used in this study to
compatibilize the blends differ in molecular weight and degree of
asymmetry of the blocks. The general Palierne model with an interfacial
shear modulus was used to analyze the dynamic measurements performed
after different shear histories. It was shown that the coalescence
suppression is more effective when the amount of compatibilizer
increases and when the overall molecular weight of the block copolymer
increases. When comparing the coalescence behaviour of a blend and the
inverse blend, it was shown that coalescence is suppressed more when the
longest block of the block copolymer is located in the matrix. The
interfacial relaxation time increases with molecular weight of the
blocks for symmetric block copolymers. Asymmetry of the blocks also
causes it to increase. A scaling relation is proposed for the
interfacial relaxation time of PI/PDMS blends. This master curve is
extended for varying viscosity ratios of the blend and with data of a
polydimethylsiloxane (PDMS)/polyisobutylene (PIB) blend and a
polymethylmethacrylate (PMMA)/polystyrene (PS) blend.
c)
Corresponding author.
Return to top.
Ronald G. Egres and Norman J. Wagner a)
Department of Chemical Engineering and
Center for Molecular and Engineering Thermodynamics
University of Delaware, Newark, Delaware 19716
Abstract
The shear rheology and shear-induced microstructure of poly(ethylene
glycol) (PEG)- based suspensions of acicular precipitated calcium
carbonate (PCC) particles of varying particle aspect ratio (nominal L/D
~ 2, 4, 7) are reported. These anisotropic particle suspensions
demonstrate both continuous and discontinuous reversible shear
thickening with increasing applied shear rate or stress similar to that
observed for suspensions of spherical colloidal particles. The critical
volume fraction for the onset of discontinuous shear thickening
decreases as the average particle aspect ratio is increased. However,
the critical stress for shear thickening is found to be independent of
particle anisotropy and volume fraction. Rather, it can be predicted
based on the minor axis diameter of the particles and is found to agree
with values for near hardsphere suspensions. Small angle neutron
scattering during shear flow (Rheo-SANS) demonstrates that long-axis
particle alignment with the flow direction is maintained throughout the
range of shear stresses investigated, including the shear thickening
regimes for both continuously and discontinuously shear thickening PCC/PEG
suspensions. Rheo-SANS and transient rheological experiments indicate
that this reversible shear thickening is a consequence of lubrication
hydrodynamic interactions and the formation of transient hydroclusters
of flowaligned particles.
a) Corresponding Author:
wagner@che.udel.edu
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Danilo C. Pozzo, Kate R. Hollabaugh and Lynn M. Walker
a)
Department of Chemical Engineering
Center for Complex Fluids Engineering
Carnegie Mellon University
Pittsburgh, PA 15213
Abstract
The mechanical properties of three-dimensionally organized
nanocomposite materials composed of nanometer-sized inorganic particles
dispersed in micelle cubic crystals is studied rheologically. The
influence of parameters including temperature, relative concentrations
and the relative size of particles and the micelles that make up the
cubic crystal are explored using oscillatory shear and creep
measurements. These parameters have a significant influence on the
mechanical properties of the final nanocomposite materials.
Additionally, we find that the properties of the samples depend strongly
on the temperature profile that is used to form the micelle crystal.
Results indicate the importance of particle-template stoichiometry and
relative particle size (to the micelle size) on the mechanical
properties of the nanocomposites.
a) Corresponding author. E-mail:
lwalker@andrew.cmu.edu
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