- Characterization of the viscoelastic behavior of
complex fluids using
the piezoelastic axial vibrator (PAV)
- Jérôme J. Crassous, Raphael Régisser, Matthias Ballauff, and Norbert
Willenbacher
- Rheology of a dispersion of low-molar-mass liquid
crystal droplets in polydimethylsiloxane
- Yong Woo Inn and Morton M. Denn
- Gel formation and collapse in a dispersion of a low
molar mass liquid crystal in a polymer matrix
- Yong Woo Inn and Morton M. Denn
- A novel “cleat” geometry for suppressing wall
slip
- Charles S. Nickerson and Julia A. Kornfield
- Origins of concentric cylinders viscometry
- Prasannarao Dontula, Christopher W. Macosko, and L. E. Scriven
- Rheopexy in highly concentrated emulsions
- Irina Masalova, Michael Taylor, Ellina Kharatiyan, and Alexander Ya.
Malkin
- Morphology development of a PS/PMMA blend during
start-up of uniaxial elongational flow
- F. Oosterlinck, M. Mours, H.M. Laun, and P. Moldenaers
- On the gap error in parallel plate rheometry that
arises from the presence of air when zeroing the gap
- Georgina A. Davies and Jason R. Stokes
- The link between discrete and continuous
modeling of liquid foam at the level of a single bubble
- B. S. Gardiner and A. Tordesillas
Jérôme J. Crassous, Raphael Régisser, and Matthias
Ballauff
Physikalische Chemie I, University of Bayreuth, 95440 Bayreuth, Germany
Norbert Willenbacher
Polymer Research Division, BASF Aktiengesellschaft, D-67056 Ludwigshafen,
Germany
Abstract
The piezoelectric axial vibrator (PAV) is a squeeze-flow rheometer
working at frequencies f between 1 and 4000 Hz. It can be used to
measure the storage modulus G´ and the loss modulus G´´ of
complex fluids in this frequency range. Using polymer solutions with
known G´ and G´´ it is shown that the PAV gives reliable
mechanical spectra for frequencies between 1 and 4000 Hz. The
measurements done with the PAV are combined with a conventional
mechanical rheometer (10-3 ≤ f ≤ 15 Hz) and a set of
torsional resonators (f = 13, 25 and 77 kHz) to obtain G´
and G´´ between 10-3 Hz and 77 kHz. Using this
combination we present the first analysis of the viscoelasticity of an
aqueous suspension of thermosensitive latex particles in this range of
frequency. It is demonstrated that the combination of the three devices
gives the entire mechanical spectra without resort to the
time-temperature superposition principle.
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Yong Woo Inn and Morton M.
Denn a)
Benjamin Levich Institute for
Physico-Chemical Hydrodynamics
and Department of Chemical Engineering
City College New York, CUNY, New York, NY 10031
Abstract
We describe the linear viscoelastic response of dispersions of droplets
of two biphenylcarbonitriles that exhibit both isotropic and liquid
crystalline phases, 4'-pentyl-4-bipheny1carbonitrile (5CB) and
4'-octyl-4-biphenylcarbonitrile (8CB), in polydimethylsiloxane (PDMS).
The Palierne emulsion model agrees well with the storage modulus data
for 8CB in both isotropic and nematic phases, but the model overpredicts
the magnitude of the interfacial relaxation in the 5CB dispersion, where
the volume fraction of the dispersed phase required to fit the data is
substantially smaller than the actual value. Similarly, the interfacial
tension of 5CB against PDMS deduced from the Palierne fit shows much
less temperature dependence than values measured with pendant drop
tensiometry. The 8CB droplets are small, with a narrow size
distribution, while the 5CB droplets are considerably larger and have a
high degree of polydispersity. The basic mechanics of the Palierne
theory appear to be applicable to nematic liquids, at least under
conditions where the entropic elasticity is weak relative to the
interfacial stress; the data suggest, however, that the theory is not
applicable to smectic systems, and it needs to be used with considerable
care with large droplets accompanied by a large degree of polydispersity.
a) Author to whom correspondence should be
addressed; e-mail:
denn@che.ccny.cuny.edu
* The editorial process for this manuscript was carried out by Editorial
Board member Paula Moldenaers.
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Yong Woo Inn and Morton M. Denn a)
Benjamin Levich Institute for Physico-Chemical
Hydrodynamics
and Department of Chemical Engineering
City College of New York, CUNY, New York, NY 10031
Abstract
A dispersion of 4'-octyl-4-biphenylcarbonitrile (8CB) in
polydimethylsiloxane (PDMS) matrix exhibits a rheological
response characteristic of a fractal gel when prepared at a temperature
at which 8CB exists in the smectic phase. The dispersion remains
gel-like throughout the smectic and nematic phases of 8CB, but collapses
irreversibly to a fluid-like dispersed droplet morphology at the nematic-isotropic
transition. The system appears to be kinetically trapped in one or the
other morphology because of a large energy barrier between the
bicontinuous gel, which is the stable morphology in the smectic regime,
and the dispersed droplet, which is the stable morphology in the nematic
regime; the energy barrier results from the homeotropic orientation of
8CB at the PDMS interface. The system thus provides an unusual
opportunity to probe the consequences of very different length scales in
the minor component in both the smectic and nematic liquid crystalline
regimes. One such consequence is a controllable thousand-fold change in
the storage modulus of the blend.
a) Author to whom correspondence should be
addressed; e-mail: denn@ccny.cuny.edu
* The editorial process for this manuscript was carried out by Editorial
Board member Paula Moldenaers.
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Charles S. Nickerson and Julia A. Kornfield
Division of Chemistry and Chemical Engineering, California
Institute of Technology
1200 E. California Blvd., Pasadena, California, USA
Abstract
We describe the use of cleated surfaces on parallel disk tools to
quantitatively measure the rheological properties of diverse slip-prone
fluids and soft materials. Densely-packed protrusions (0.45mm
× 0.45mm cross section × 0.6mm length, 0.9mm apart)
penetrate the slip layer, preventing significant flow between cleats.
This creates a no-slip boundary ~0.16mm below their tips, which serves
as the sample gap boundary, in direct analogy to the parallel plate
geometry. This “cleat” geometry suppresses slip without application of
significant normal force, it imposes well-defined shear to enable
absolute measurements and is compatible with small sample volumes. The
geometry is validated in steady and oscillatory shear using a series of
materials not prone to slip (Newtonian oils and an entangled polymer
melt). The advantage of cleated tools over other slip-prevention methods
is demonstrated using increasingly challenging materials – an emulsion
(mayonnaise), a suspension (peanut butter), and a biological tissue
(porcine vitreous humor).
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Prasannarao Dontula a), Christopher W.
Macosko b), and L. E. Scriven
Department of Chemical Engineering & Materials Science,
University of Minnesota, Minneapolis, MN 55455, U.S.A.
Abstract
The history of the concentric cylinders apparatus for measuring the
shear viscosity of liquids, and its attribution to Maurice Couette have
been explored. Examination of the Nineteenth Century literature has
revealed that the concept goes back to Stokes and later Margules, the
design and execution of the apparatus, apparently independently, to
Perry, Couette, Mallock, and Schwedoff. Mallock's and Schwedoff's
measurements were the most accurate and were within 1 % of the
viscosities derived from Poiseuille's measurements, on the basis of no
slip at the tube walls and cylinder surfaces. Measurement of fluid
viscosity was closely linked to the adoption of the no-slip boundary
condition at solid-fluid interfaces.
* This paper based on a portion of C. W. Macosko’s 2004
Bingham Medal address, 15 February 2005, Lubbock, TX.
a) Current address: Unilever Research & Development Vlaardingen,
Home & Personal Care, Olivier van Noortlaan 120, 3130 AC Vlaardingen, The
Netherlands.
b) To whom correspondence should be addressed. E-mail:
macosko@tc.umn.edu
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Irina Masalova a,c), Michael Taylor b),
Ellina Kharatiyan a), and Alexander Ya. Malkin a)
a) Cape Peninsula University of Technology,
Faculty of Engineering, Department of Civil Engineering, PO Box 652, Cape
Town 8000, Republic of South Africa
b) African Explosive Limited, Johannesburg,
Republic of South Africa
Abstract
This work is describes a detailed study of the rheopectic effect in the
flow of highly concentrated emulsions at low stresses. Experiments with
the shear rate sweep demonstrated that the upward and downward branches
of the flow curves coincide above some specific shear rate value. The
upward experiments show the existence of the Newtonian part on the flow
curve in the low-shear-rate domain, while the effect of yielding is
observed in the downward curve. Restoration of the initial structure
(and properties) after cessation of loading occurs very quickly. This
allows associating the rheopexy with elastic deformations and the
relaxation process (observed in frequency dependence of dynamic moduli)
with characteristic times of about 0.03s. Transient processes proceed in
the range of shear deformation of the order of several units. Some
quantitative measures of the rheopectic behaviour are proposed and
discussed. Normal stresses are constant in the low shear stress domain,
but decrease sharply above the range of rheopectic behaviour. The
mechanisms of the observed effects are discussed. Temperature is not an
important factor in the rheopectic behaviour studied in this work.
c) Author to whom correspondence should be
addressed; e-mail:
masalovai@cput.ac.za
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F. Oosterlinck a), M. Mours b),
H.M. Laun b), and P. Moldenaers a,c)
a) K.U. Leuven, Department of Chemical
Engineering
W. de Croylaan 46, B-3001 Leuven, Belgium
b) Polymer Research, BASF Aktiengesellschaft
D-67056 Ludwigshafen, Germany
Abstract
The morphology development
of a PS/PMMA blend has been investigated during uniaxial elongational
flow. For this purpose linear conservative dichroism measurements are
used to gather time-resolved information and Scanning Electron
Microscopy (SEM) is performed on quenched samples. With the former
technique the evolution of the droplet deformation in a
semi-concentrated blend is studied in real time, whereas the latter
technique was used for imaging individual droplets after the elongation.
It is shown that the droplet deformation is affine for the conditions
under investigation and that it is possible to predict the evolution of
the dichroism by existing theories and the assumption of affine
deformation. It has also been verified whether rheological measurements
can be used to deduce morphological information during elongational
flow, as this method has been succesfully applied previously in simple
shear flow.
c)
Corresponding author.
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Georgina A. Davies and Jason R. Stokes
Unilever Corporate Research
Unilever R&D Colworth
Colworth House
Sharnbrook, Bedfordshire
MK44 1LQ
United Kingdom
Abstract
When zeroing the gap between two parallel plates, the squeeze flow of
air results in a detectable normal force at a finite height that is
misinterpreted in rheometry as an indicator for the zero gap position.
This leads to a substantial gap error using well aligned parallel plates
that is accurately predicted using Stefan’s equation for squeeze flow.
Minimizing or accounting for this error enables accurate rheological
measurements to be performed in torsional flow using the parallel plate
geometry at narrow gap heights, thus allowing shear rates of over 105
s-1 to be achieved.
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B. S. Gardiner a) and A. Tordesillas b,c)
a) Department of Civil and Environmental
Engineering, The University of Melbourne, Australia
b) Department of Mathematics and Statistics,
The University of Melbourne, Australia
Abstract
In order to test the adaptability of a novel homogenization scheme
originally developed for dry granular media, a micromechanical
constitutive law for three-dimensional monodisperse wet foam is
developed. The advantage of the homogenization scheme is that it
provides a link between the discrete bubble-scale microstructure and the
continuum quantities of stress and deformation. Furthermore, the
resulting constitutive law is in terms of physical material properties
(e.g. fluid viscosity, surface tension, bubble radius) rather than the
more phenomenological parameters like power-law indices etc. Hence,
predictions of the continuum model can be, and are, compared directly to
experiments and simulations. Many of the general features of foam
behavior are reproduced, including small-strain elasticity, dependence
on gas fraction, and Bingham plastic type deformation rate dependency.
However, the current micromechanical continuum model substantially
overestimates the static shear modulus and yield stress of foams in
comparison to simulations and experiments. This discrepancy is due to
the adoption of a mean-field assumption for the deformation in the
current model. It is then argued that future micromechanical continuum
models for foams cannot neglect the non-affine motions associated with
bubble rearrangements. Finally, for both foams and granular materials,
our study indicates that the uniform deformation assumption is only
valid near the critical packing of monodisperse spherical particles.
c) Corresponding author.
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