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Nov 1995

Volume 39, Issue 6, pp. 1095-1534


Orthotropic closure approximations for flow‐induced fiber orientation

Joaquim S. Cintra and Charles L. Tucker

J. Rheol. 39, 1095 (1995); http://dx.doi.org/10.1122/1.550630 (28 pages) | Cited 23 times

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A new family of closure approximations, called orthotropic closures, is developed for modeling of flow‐induced fiber orientation. These closures approximate the fourth‐order moment tensor for fiber orientation in terms of the second‐order moment tensor. Key theoretical concepts are that any approximate fourth‐order tensor must be orthotropic, that its principal axes must match those of the second‐order tensor, and that each principal fourth‐order component is a function of just two principal values of the second‐order tensor. Examples of orthotropic closures are presented, including a simple form based on linear interpolation and a formula that is fitted to numerical solutions for the probability density function. These closures are tested against distribution function solutions in a variety of flow fields, both steady and unsteady, by integrating the orientation evolution equation. A scalar measure of the difference between the exact and approximate second‐order tensors quantifies the errors of various closures. The orthotropic fitted closure is shown to be far more accurate than any earlier closure approximation, and slightly more accurate than Verleye and Dupret’s natural closure. Approaches for further increasing the accuracy of orthotropic closures and ultimate limits to the accuracy of any closure approximation are discussed. © 1995 Society of Rheology
Show PACS
83.10.Kn Reptation and tube theories
83.10.Mj Molecular dynamics, Brownian dynamics
83.80.Hj Suspensions, dispersions, pastes, slurries, colloids
83.80.Iz Emulsions and foams

Apparent wall slip velocity coefficients in concentrated suspensions of noncolloidal particles

S. C. Jana, B. Kapoor, and A. Acrivos

J. Rheol. 39, 1123 (1995); http://dx.doi.org/10.1122/1.550631 (10 pages) | Cited 23 times

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The apparent wall slip velocity coefficient of concentrated monodisperse suspensions of 90 μm PMMA particles in a viscous Newtonian fluid was determined experimentally in a narrow gap Couette device by measuring the particle velocities across the gap using a laser doppler anemometer system and then extrapolating the results to the two walls. The slip coefficients thereby obtained were found to be insensitive to the magnitude of the applied shear rate and to equal, approximately, λ/8 for particle concentrations ϕ in the range 0.45≤ϕ≤0.52, where λ refers to the relative effective viscosity of the suspension with respect to that of the pure fluid. © 1995 Society of Rheology
Show PACS
83.10.Kn Reptation and tube theories
83.10.Mj Molecular dynamics, Brownian dynamics
83.50.Lh Slip boundary effects (interfacial and free surface flows)
83.80.Hj Suspensions, dispersions, pastes, slurries, colloids
83.80.Iz Emulsions and foams

Comparison of constitutive equations for polymer solutions in uniaxial extension

V. Tirtaatmadja and T. Sridhar

J. Rheol. 39, 1133 (1995); http://dx.doi.org/10.1122/1.550632 (28 pages) | Cited 13 times

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The Oldroyd‐B, Giesekus, FENE‐P, and White–Metzner models are used to predict the uniaxial extensional stress growth results of two ideal elastic fluids and a shear‐thinning fluid. The model predictions are compared with the data obtained, at constant deformation rates, using the filament stretching technique. The linear viscoelastic parameters for the models were obtained by fitting the Oldroyd‐B equations to the dynamic data. For the Giesekus and FENE‐P models, the extra nonlinear parameters were obtained by fitting the model predictions to the steady shear data. The parameters for the White–Metzner model (using Carreau‐type equation) were also obtained by directly fitting the steady shear data. For the ideal elastic fluids, Oldroyd‐B, Giesekus, and FENE‐P models with multiple modes of relaxation times generally provide good predictions of the extensional stress growth at small strain, but not particularly well at high strain. While the Oldroyd‐B model predicts infinite extensional viscosity at finite extension rates, the Giesekus and FENE‐P models predict steady extensional viscosities which are of the correct order of magnitude. The FENE‐P equation also shows a more abrupt approach to steady state, similar to that observed experimentally. For the shear‐thinning fluid the Giesekus and FENE‐P models fail to predict the large stresses found in extensional flow. On the other hand, the White–Metzner model, while unable to predict the extensional stress growth for the ideal elastic fluids, is an improvement over the Oldroyd‐B model for the shear‐thinning fluid. © 1995 Society of Rheology
Show PACS
83.10.Gr Constitutive relations
83.50.Jf Extensional flow and combined shear and extension
83.80.Hj Suspensions, dispersions, pastes, slurries, colloids
83.80.Iz Emulsions and foams

Continuum dynamic behavior of homogeneous liquid‐crystalline polymers under the imposition of shear and magnetic fields

N. C. Andrews, B. J. Edwards, and A. J. McHugh

J. Rheol. 39, 1161 (1995); http://dx.doi.org/10.1122/1.550633 (21 pages) | Cited 5 times

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An analysis of the dynamic behavior of polymeric liquid crystals is given in terms of a second‐rank order parameter tensor describing the orientational state of the local microstructure. The continuum equations governing the dynamics of the material are analyzed under both steady‐state and transient conditions for isotropic and liquid‐crystalline fluids subjected to shear and magnetic fields. Analysis reveals that a great variety of dynamic behavior for liquid‐crystalline materials can be accommodated within the framework of a continuum theory in terms of a second‐rank order parameter tensor, and that this dynamic behavior approximates well the orientational behavior obtained with the more complex distribution function theories. Under some conditions the associated rheological behavior of the continuum theory exhibits discrepancies in the normal stress behavior compared to rheological calculations based on the distribution function theory. For simultaneous application of shear and magnetic fields, both the direction and the strength of the magnetic field play a major role in determining the dynamic system response. © 1995 Society of Rheology
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83.10.Gr Constitutive relations
83.60.Np Effects of electric and magnetic fields
83.80.Xz Liquid crystals: nematic, cholesteric, smectic, discotic, etc.

Linear viscoelastic properties of ordered latices

B. van der Vorst, D. van den Ende, and J. Mellema

J. Rheol. 39, 1183 (1995); http://dx.doi.org/10.1122/1.550634 (18 pages) | Cited 8 times

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The frequency‐dependent behavior of the storage modulus G′ and loss modulus G″ has been measured for an ordered latex at different volume fractions. From these measurements the volume fraction dependency of the static shear modulus was obtained. The theoretical static shear modulus has been deduced from a stress tensor expression which only takes into account the electrostatic pair interactions between nearest neighbors. The electrostatic pair interaction is modeled adequately to account for the multiparticle environment of a particle and for high surface charges. The interactions are described by the linear superposition approximation for the pair interaction energy between two particles given by Bell et al. [J. Colloid Interface Sci. 33, 335 (1970)]. The apparent surface potential and the effective Debije screening length used in this expression are determined from the electrostatic potential which is numerically determined from the Poisson–Boltzmann equation in a spherical cell. The theoretical model is also compared with measurements of several other investigators. Most of the experimental data can be scaled to a single mastercurve resulting from the proposed theoretical model. © 1995 Society of Rheology
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83.60.Bc Linear viscoelasticity
83.80.Hj Suspensions, dispersions, pastes, slurries, colloids
83.80.Iz Emulsions and foams

Use of coupled birefringence and LDV studies of flow through a planar contraction to test constitutive equations for concentrated polymer solutions

L. M. Quinzani, R. C. Armstrong, and R. A. Brown

J. Rheol. 39, 1201 (1995); http://dx.doi.org/10.1122/1.550725 (28 pages) | Cited 7 times

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Laser Doppler velocimetry and flow‐induced birefringence are used to measure the rate of deformation and the principal components of the refractive index tensor in a 5% polyisobutylene (PIB) solution in tetradecane (C14) flowing along the centerplane of an abrupt 3.97:1 planar contraction. The stress optical law is used to interpret the birefringence data in terms of the normal stress difference, which is used to calculate a transient elongational viscosity defined along the centerplane. These measurements are compared directly to predictions of six multimode, differential constitutive models (Oldroyd‐B, White–Metzner, Acierno et al., Giesekus, Bird–DeAguiar, and Phan‐Thien–Tanner) that are fit to steady and small amplitude oscillatory shear flow data for the PIB/C14 solution. The fluid exhibits slight elongational thickening followed by apparent extensional thinning at higher elongation rates. We believe that this ‘‘thinning’’ behavior is due to the decreased residence time of the polymer molecules in the high‐strain‐rate region as the flow rate (and maximum elongation rate) is increased. The nonlinear constitutive equations, except for the White–Metzner model, are virtually indistinguishable in their description of the dynamical response of the fluid in this experiment; however, the Phan‐Thien–Tanner model gives the best quantitative fit to the data. These results point to the need for experiments in which the fluid flowing along the centerline is subjected to a greater total elongational strain. © 1995 Society of Rheology
Show PACS
83.50.Jf Extensional flow and combined shear and extension
83.80.Rs Polymer solutions
83.80.Sg Polymer melts
83.85.Ei Optical methods; rheo-optics

Chaotic rheological parameters of periodically forced suspensions of slender rods in simple shear flow

K. Satheesh Kumar and T. R. Ramamohan

J. Rheol. 39, 1229 (1995); http://dx.doi.org/10.1122/1.550729 (13 pages) | Cited 4 times

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See Also: Erratum

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We demonstrate for the first time that the rheological parameters like the apparent viscosities and the first and second normal stress differences of suspensions of orientable particles can show chaotic behavior when the orientation vector evolves chaotically. We also demonstrate that the range of the values of the rheological parameters is about 10 000 times greater when the parameters evolve chaotically. This suggests that a wide range of properties may be obtained by small variations in controllable parameters. When coupled with suitable control of chaos algorithms, a wide range of suspension behavior is thus possible since a chaotic solution can be considered as an unlimited reservoir of periodic solutions of arbitrary period. © 1995 Society of Rheology
Show PACS
83.10.Gr Constitutive relations
83.80.Hj Suspensions, dispersions, pastes, slurries, colloids
83.80.Iz Emulsions and foams
83.80.Gv Electro- and magnetorheological fluids

Viscoelastic flow past a confined cylinder of a polyisobutylene solution

Hans P. W. Baaijens, Gerrit W. M. Peters, Frank P. T. Baaijens, and Han E. H. Meijer

J. Rheol. 39, 1243 (1995); http://dx.doi.org/10.1122/1.550635 (35 pages) | Cited 2 times

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Viscoelastic constitutive equations are evaluated using the benchmark problem of the planar flow past a confined cylinder for a well‐characterized solution of 5%(w/w) polyisobutylene in tetradecane. The ratio of channel height to cylinder diameter is equal to two. We compare finite element simulations with point‐wise measured velocities and stresses obtained by means of laser Doppler anemometry and a flow‐induced birefringence technique, respectively. The Deborah number (De) ranges from 0.25 to 2.32. In the case of the geometry with a symmetrically confined cylinder, computations were made with a generalized Newtonian model and with both a single‐ and a four‐mode Phan‐Thien and Tanner (PTT) model. All model parameters were determined in simple shear flow. A similar analysis is presented in case of an asymmetrically confined cylinder (with De=1.87). Impressively good agreement was found between the predictions of the four‐mode PTT model and the measured velocities and stresses. The agreement was even excellent in the geometry with the asymmetrically confined cylinder. © 1995 Society of Rheology
Show PACS
83.10.Gr Constitutive relations
83.60.Bc Linear viscoelasticity
83.80.Rs Polymer solutions
83.80.Sg Polymer melts
83.85.Ei Optical methods; rheo-optics

Numerical simulation of viscoelastic flow around a cylinder using an integral constitutive equation

G. Barakos and E. Mitsoulis

J. Rheol. 39, 1279 (1995); http://dx.doi.org/10.1122/1.550636 (14 pages) | Cited 1 time

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Numerical simulations have been undertaken for the flow of a 5 wt. % polyisobutylene (PIB) solution in tetradecane (C14) around a cylinder placed between parallel plates. The PIB solution has been the subject of an extensive rheological characterization and the flow geometry corresponds to the one used in a previous study for laser Doppler anemometry and flow‐induced birefringence measurements. The constitutive equation used is an integral‐type K‐BKZ model with a relaxation spectrum, which fits well experimental data for the shear and elongational viscosities and the normal stresses as measured in shear flow. Stable numerical solutions have been obtained and used to compare the K‐BKZ model predictions with the experimental data reported recently by Baaijens. The velocity and shear stress values predicted by the simulation are in excellent agreement with the experimental ones. Very good agreement is also obtained for the predictions of the first normal stress difference both before and after the cylinder, in sharp contrast with previous experimental results, which had shown a much slower relaxation of the stresses. The drag force exerted by the fluid on the cylinder has been calculated and reported to be a decreasing function of the Deborah number De. © 1995 Society of Rheology
Show PACS
47.11.-j Computational methods in fluid dynamics
83.10.Rs Computer simulation of molecular and particle dynamics
83.60.Bc Linear viscoelasticity
83.80.Rs Polymer solutions
83.80.Sg Polymer melts

The multipass rheometer

M. R. Mackley, R. T. J. Marshall, and J. B. A. F. Smeulders

J. Rheol. 39, 1293 (1995); http://dx.doi.org/10.1122/1.550637 (17 pages) | Cited 13 times

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This article describes the technical performance and initial results for a new, two‐piston, ‘‘multipass rheometer.’’ Fluid is contained within a capillary by two servo‐hydraulically controlled pistons. Both steady flow and oscillatory data can be obtained from the device with mean pressure as an independent adjustable variable. Steady and oscillatory data are presented for a silicone oil and a viscoelastic solution and certain data are compared with results obtained from a Rheometrics RDS‐II mechanical spectrometer or with literature data. The results show that the multipass rheometer is capable of extending the experimental ranges of many conventional rheometers, particularly in terms of pressure control, high shear rates, and multiple, successive flow measurements. © 1995 Society of Rheology
Show PACS
47.80.-v Instrumentation and measurement methods in fluid dynamics
83.85.Cg Rheological measurements—rheometry
83.85.Jn Viscosity measurements

Shear‐induced microstructural changes in flocculated suspensions of fumed silica

Srinivasa R. Raghavan and Saad A. Khan

J. Rheol. 39, 1311 (1995); http://dx.doi.org/10.1122/1.550638 (15 pages) | Cited 4 times

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Suspensions of fumed silica exhibit a wide range of rheological properties, depending on the type of microstructure present. At high silica concentrations, the rheological behavior is ‘‘gel‐like,’’ due to the formation of a network consisting of interconnected silica flocs. When large amplitude oscillatory preshear is applied on these systems, the network linkages are disrupted, resulting in the formation of isolated flocs. In this study, we focus on the extent to which the network is restored on cessation of preshear. By applying small amplitude oscillations we can study the development of the elastic modulus (G′) with time, following disruptive shear. We find that the restoration of the network after preshear is instantaneous; however, G′ recovers to different levels depending on the amplitude of the imposed preshear strain. Contrary to expectations, larger preshear strains (which cause a greater degree of microstructural disruption) do not always lead to lower levels of recovered G′. For strains greater than a critical value, the recovered G′ progressively increases with increasing preshear strain. This anomalous behavior of the elastic modulus is explained in terms of microstructural rearrangements that may occur during oscillatory preshear. © 1995 Society of Rheology
Show PACS
83.10.Gr Constitutive relations
83.60.Bc Linear viscoelasticity
83.80.Hj Suspensions, dispersions, pastes, slurries, colloids
83.80.Iz Emulsions and foams

Effects of nonuniform electric field on slit flow of an electrorheological fluid

Basim Abu‐Jdayil and Peter O. Brunn

J. Rheol. 39, 1327 (1995); http://dx.doi.org/10.1122/1.550639 (15 pages) | Cited 1 time

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In this work, slit flow of an electrorheological (ER) fluid is studied via laser Doppler anemometry under nonuniform electric‐field conditions. For that purpose, the electrodes were coated with a PVC foil. Under ac conditions the ER effect with homogeneous coating was smaller than in the case of no coating. Yet, as soon as holes were punched in the foil, the ER effect greatly increased, exceeding the effect of the uncoated electrodes. Irrespective of the type of coating applied, the electric current remained the same. This contrasts with the results under dc conditions where (i) the ER effect with coating (irrespective of the type of coating) was smaller (or even zero) than without coating and where (ii) a decrease of the ER effect always was accompanied by a decrease in electric current. No electric current implied no ER effect, irrespective of the strength of the applied electric field. © 1995 Society of Rheology
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83.80.Gv Electro- and magnetorheological fluids
83.85.Cg Rheological measurements—rheometry

The density dependence of fluid properties and non‐Newtonian flows: The Weissenberg effecta)

J. C. Rainwater, H. J. M. Hanley, and A. Narayan

J. Rheol. 39, 1343 (1995); http://dx.doi.org/10.1122/1.550640 (17 pages)

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Two approaches which describe the Weissenberg effect (height profile of a non‐Newtonian fluid between rotating vertical concentric cylinders) are discussed. The first is based on an earlier calculation with rheological properties of a simple liquid obtained from nonequilibrium molecular dynamics (NEMD). The calculation is redone here using new results on the density dependence of the normal pressure differences. The NEMD calculations are restricted to Couette flow, but describe specifically, in a consistent manner, the effects of finite compressibility. The pressure, viscosity, and normal pressure differences are all found from NEMD to be sensitive functions of density, which requires that the equations of motion be solved iteratively and self‐consistently, and a sample calculation is presented for the soft sphere fluid. The second approach is that of Joseph and Fosdick. Their assumptions and techniques are examined and compared with the NEMD calcula‐ tions.
Show PACS
47.50.-d Non-Newtonian fluid flows
83.60.Hc Normal stress differences and their effects (e.g. rod climbing)
47.11.-j Computational methods in fluid dynamics

Uniformly valid approximations for the conformational integrals resulting from Gaussian closure in the Hookean dumbbell model with internal viscositya)

R. Sureshkumar and Antony N. Beris

J. Rheol. 39, 1361 (1995); http://dx.doi.org/10.1122/1.550641 (24 pages)

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We consider a computationally more efficient calculation of the conformational integrals resulting from applying a Gaussian closure to evaluate the higher moments of the end‐to‐end vector, Q, in the Hookean dumbbell model with internal viscosity. First, these integrals are expressed as functions of the eigenvalues of the chain conformation tensor 〈QQ〉. Subsequently, they are evaluated analytically in certain characteristic limiting cases. These results are then used to construct uniformly valid approximations for the integrals. The relative error incurred in these approximations, as measured by a comparison with the results obtained through a direct numerical evaluation, has been shown to be uniformly small, i.e., less than a few percent, in the entire parameter space. Further validation of the approximations to the integrals is provided from the results obtained for the shear viscosity and first normal stress difference as a function of shear rate in a steady, homogeneous shear flow which are in excellent agreement with those provided in the literature also using the Gaussian closure. The approximations are subsequently used to predict the response of the model to the startup of simple shear flow. Excellent agreement is found with the previously reported results using the Gaussian closure in this case as well. Most important, the reduction of computational workload through the use of the approximations to the conformational integrals makes it possible for this model to be used in more complicated flow simulations. As an illustrative example, we provide numerical results for the flow variables in a steady channel Poiseuille flow. © 1995 Society of Rheology
Show PACS
83.10.Kn Reptation and tube theories
83.10.Mj Molecular dynamics, Brownian dynamics
83.50.Ax Steady shear flows, viscometric flow
83.60.Bc Linear viscoelasticity
83.80.Rs Polymer solutions
83.80.Sg Polymer melts

Effects of molecular weight distribution on dynamic viscoelasticity and biaxial extensional flow behavior of polystyrene melts

N. Golshan Ebrahimi, M. Takahashi, O. Araki, and T. Masuda

J. Rheol. 39, 1385 (1995); http://dx.doi.org/10.1122/1.550642 (13 pages) | Cited 2 times

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Dynamic viscoelasticity and biaxial extensional flow behavior of polystyrene melts with various molecular weight distributions have been studied in wide ranges of temperature and strain rate ϵ̇B. Two patterns of time dependence of the biaxial stress growth coefficient η+B are observed with increasing reduced strain rate ϵ̇Bτ0, where τ0 is a characteristic relaxation time. At short times, η+B coincides with the linear viscoelastic curve; then it shows strain hardening after that, or strain softening followed by a quasisteady state. These behaviors are observed for polydisperse polystyrenes at much higher ϵ̇Bτ0 than those for monodisperse polystyrenes. The quasisteady‐state viscosity ηB,qs decreases with the strain rate. Addition of a very high molecular weight component causes considerable effects on τ0 and on the strain rate dependences of shear ‖η∗‖ and biaxial ηB,qs viscosities as well as on the stress growth coefficient η+B, where ‖η∗‖ is the absolute value of the complex viscosity. The relaxation time τ0 increases very much, and the strain rate dependences of ‖η∗‖ and ηB,qs become much weaker. The upturn tendency of η+B becomes prominent when compared at the same reduced strain rate ϵ̇Bτ0. On the other hand, when compared at the same value of the reduced viscosity ηB,qs/6η0, a similar degree of strain softening in η+B is observed for all polydisperse samples, where η0 is the zero shear viscosity. © 1995 Society of Rheology
Show PACS
83.10.Gr Constitutive relations
83.60.Bc Linear viscoelasticity
83.50.Jf Extensional flow and combined shear and extension
83.80.Rs Polymer solutions
83.80.Sg Polymer melts

Shear‐thickening and flow‐induced structure in a system of DMSO containing waxy maize starcha)

F. R. Dintzis, E. B. Bagley, and F. C. Felker

J. Rheol. 39, 1399 (1995); http://dx.doi.org/10.1122/1.550643 (11 pages) | Cited 1 time

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Waxy maize starch in the solvent 90%DMSO–H2O exhibited the phenomena of shear‐thickening, quasihysteresis loops of shear stress versus strain rate that were anticlockwise and flow‐induced structure that was observed with phase contrast microscopy. These phenomena were not seen with normal maize starch and an enriched fraction of normal maize amylopectin. The ability of a waxy maize starch sample to have these properties could be destroyed by severe treatment. We consider the flow properties of shear‐thickening and anticlockwise shear stress/strain rate loops to be indicative of a flow‐induced structure that occurs with waxy maize starch amylopectin. Because these effects do not occur with normal maize starch we infer that there is a significant structural difference between the amylopectins of waxy maize starch versus normal maize starch.
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83.10.Gr Constitutive relations
83.85.Cg Rheological measurements—rheometry

Comparison of sphere‐size distributions obtained from rheology and transmission electron microscopy in PMMA/PS blends

Chr. Friedrich, W. Gleinser, E. Korat, D. Maier, and J. Weese

J. Rheol. 39, 1411 (1995); http://dx.doi.org/10.1122/1.550720 (15 pages) | Cited 10 times

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Often, blends of two immisible polymers have a morphology with one component building a matrix in which spherical inclusions of the other component are embedded. The rheological response of such blends contains an elastic contribution which can be attributed to the form relaxation of the inclusions. This process has a characteristic relaxation time which is proportional to the radius of the inclusions divided by the interfacial tension between the blends’ components. Thus a distribution of radii leads to a distribution of relaxation times. It is shown that rheological data together with an emulsion model can be used to determine the volume weighted sphere‐size distribution up to a scaling depending on the interfacial tension. The procedure is applied to data of four PMMA/PS blends and the results are compared with the corresponding distributions obtained from transmission electron microscopy (TEM). If the concentration of the spherical inclusions is small, both results are in excellent agreement. For larger concentrations, deviations between the results from rheology and TEM are observed. © 1995 Society of Rheology
Show PACS
83.10.Gr Constitutive relations
83.80.Hj Suspensions, dispersions, pastes, slurries, colloids
83.80.Iz Emulsions and foams
83.85.Cg Rheological measurements—rheometry

Guest Editorial: Proceedings of the Boston Symposium on Food Rheology, October 17–21, 1993

Jozef L. Kokini

J. Rheol. 39, 1427 (1995); http://dx.doi.org/10.1122/1.550644 (1 page)

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Abstract Unavailable
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83.80.Lz Physiological materials (e.g. blood, collagen, etc.)

Kinetics of biopolymer gelation—Implications of a cascade theory description for the concentration, molecular weight, and temperature dependences of the shear modulus and gel time

A. H. Clark and D. B. Farrer

J. Rheol. 39, 1429 (1995); http://dx.doi.org/10.1122/1.550645 (16 pages)

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The kinetic progress of biopolymer gelation is measured in terms of the shear modulus–time curve available from mechanical spectroscopy. Attention is focused on the gel time, and on the limiting value of the modulus attained at long time. A theoretical treatment of these quantities is presented based on cascade theory. This model can take on a reversible, or irreversible, form depending on differential equations defining the growth of the degree of cross‐linking α(t), i.e., depending on whether a crosslink equilibrium is assumed or permanent branched crosslinking competes with irreversible intramolecular cyclization. Application of this model to limiting modulus–concentra‐ tion and modulus–temperature data is illustrated using results for a low DE pectin–calcium system. The model’s ability to explain modulus–molecular weight data is also demonstrated using literature data for kappa carrageenan gels. Where gel time–concentration data are concerned, success is much more limited, however, and this problem is discussed. © 1995 Society of Rheology
Show PACS
83.10.Kn Reptation and tube theories
83.10.Mj Molecular dynamics, Brownian dynamics
83.80.Rs Polymer solutions
83.80.Sg Polymer melts
87.15.-v Biomolecules: structure and physical properties

Small and large deformation studies of protein gels

Mats Stading, Maud Langton, and Anne‐Marie Hermansson

J. Rheol. 39, 1445 (1995); http://dx.doi.org/10.1122/1.550646 (6 pages)

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The rheological behavior of protein gels with different network and strand structures has in a series of studies been investigated to elucidate how the structure of the gel influences its rheological properties. Nondestructive viscoelastic measurements and fracture techniques were used and the different types of structures studied were fine‐stranded gels and particulate gels. The influence of spatial inhomogeneities in the network structure was also investigated. The protein gel chosen as the model system was β‐lactoglobulin which forms gels on heating and develops different structures depending on pH: a particulate network at intermediate pH (4–6) and a fine‐stranded network below and above this interval. It can also form inhomogeneous networks depending on pH or heating rate. The fine‐stranded and the particulate gels had totally different mechanical properties. It was shown that the strand structure influenced both the modulus as well as the fracture properties of both fine‐stranded and particulate gels. Inhomogeneities induced by a slow heating rate also changed the mechanical properties the gels. © 1995 Society of Rheology
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83.80.Rs Polymer solutions
83.80.Sg Polymer melts
83.60.Bc Linear viscoelasticity
87.15.-v Biomolecules: structure and physical properties

Structure–property relationships in food biopolymer gels and solutions

Simon B. Ross‐Murphy

J. Rheol. 39, 1451 (1995); http://dx.doi.org/10.1122/1.550610 (13 pages) | Cited 4 times

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This paper serves as a review of work performed in the author’s and his collaborators’ laboratories over the last 15 years on the general topic of structure/property relationships for biopolymer (including food biopolymer) solutions and gels. In the first part, we describe how small deformation oscillatory measurements have enabled a distinction to be made between ‘‘entanglement networks,’’ ‘‘strong’’ and ‘‘weak’’ gels used, respectively, as food thickeners, gels, and stabilizers. At small enough strains both strong and weak gel systems give essentially the same mechanical spectrum, with G′≳G″, and with both moduli largely independent of frequency. However, the deformation dependence of these two classes of materials is very different. At large deformations strong gels will rupture and fail, while weak gels flow without fracture and but show recovery of solid (gel‐like) character. In this paper the various classes of food biopolymers are described, and their rheological properties related to differences in structure. The final part contrasts the behavior of a weak gel (xanthan gum) and entanglement solution (guar gum). This distinction is confirmed by their respective responses in start shear experiments. Guar solutions behave much like most other polymer solutions, whereas xanthan solutions show a very pronounced overshoot peak at low strains, and very long peak overshoot recovery times. © 1995 Society of Rheology
Show PACS
83.10.Gr Constitutive relations
83.60.Bc Linear viscoelasticity
83.80.Rs Polymer solutions
83.80.Sg Polymer melts
83.80.Lz Physiological materials (e.g. blood, collagen, etc.)

Simulation of the nonlinear rheological properties of gluten dough using the Wagner constitutive model

C. F. Wang and J. L. Kokini

J. Rheol. 39, 1465 (1995); http://dx.doi.org/10.1122/1.550611 (18 pages) | Cited 3 times

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The Wagner theory was used for gluten dough with 55% moisture content. Using the generalized Maxwell model with 24 parameters it was possible to simulate the linear memory function required in the Wagner formulation. The generalized Maxwell model also allowed prediction of the dynamic viscosity η′ and the out‐of‐phase component of the complex viscosity divided by frequency η′/ω in the frequency range studied. A damping function with two exponential terms was found to be suitable to simulate the nonlinear properties. With the incorporation of the linear memory function and the damping function, the Wagner model is able to predict the nonlinear relaxation modulus as well as the steady viscosity. © 1995 Society of Rheology
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82.80.Bg Chromatography
83.10.Gr Constitutive relations
83.60.Bc Linear viscoelasticity
83.80.Lz Physiological materials (e.g. blood, collagen, etc.)

Effects of thermomechanical processing on viscosity behavior of corn starches

F. R. Dintzis and E. B. Bagley

J. Rheol. 39, 1483 (1995); http://dx.doi.org/10.1122/1.550719 (13 pages)

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A waxy, a dent, and a high amylose starch were subjected to thermomechanical processing of varying degrees of severity. These treatments ranged from gentle dissolution in 90%DMSO to autoclaving, at temperatures up to 180 °C, to jet‐cooking. The treatments had major effects on viscosities of the starch dispersions and in particular on the intrinsic viscosities, which were determined to provide a relative measure of the molecular sizes of the processed starches. The intrinsic viscosities, from the least severe treatment to the most severe treatment, were 220 and 91; 181 and 104; 105–80 ml/g, respectively, for the waxy, dent, and high amylose starches. An unexpected characteristic of processed waxy maize was that the viscosity of 6% dispersions was extremely sensitive to intrinsic viscosity changes in the narrow range of 180–165 ml/g. In contrast, viscosities of waxy maize dispersions were relatively insensitive to changes in the lower intrinsic viscosity values (<160 ml/g) caused by more severe treatments. Dispersions of jet‐cooked waxy maize exhibited Newtonian flow; jet‐cooked dispersions of high amylose starch did not.
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81.40.Gh Other heat and thermomechanical treatments
83.60.Bc Linear viscoelasticity
83.80.Lz Physiological materials (e.g. blood, collagen, etc.)

Complexation induced changes of rheological properties of starch systems at different moisture levels

Béatrice Conde‐Petit and Felix Escher

J. Rheol. 39, 1497 (1995); http://dx.doi.org/10.1122/1.550612 (22 pages) | Cited 1 time

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Starch, especially the linear amylose fraction, is able to form helical inclusion compounds or complexes with molecules like flavor compounds, fatty acids, and emulsifiers. The effects of starch complexation on rheological properties were studied (a) in aqueous dispersions of 1%–4% starch content, (b) in high‐concentration gels of 40% starch content, and (c) in extrusion cooked low moisture starch blends. Complexation was followed by iodine binding capacity of starch and by differential scanning calorimetry. Rheological characterization was based on dynamic and steady shear measurements and on uniaxial force deformation tests. At low starch concentrations, the addition of complexing emulsifiers and flavor compounds induced gelation, provided that enough amylose was solubilized and swollen granules were present. Likewise, freshly prepared high‐concentration starch gels with the addition of complexing ligands exhibited higher moduli of deformability than control samples without additives. The sequence of moduli of elasticity became inverse during storage as complexation lowered the rate of amylose retrogradation. Melt viscosity during cooking extrusion increased with the addition of both complexing emulsifiers and noncomplexing triglycerides, while paste viscosity of ground extrudates increased with emulsifiers but not with triglycerides. Influence of starch complexation seems to be parallel for all moisture levels indicating that the main feature is the formation of insoluble amylose complexes which in turn lead to the formation of a firmer network between the dispersed starch granules. © 1995 Society of Rheology
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83.50.Jf Extensional flow and combined shear and extension
83.80.Lz Physiological materials (e.g. blood, collagen, etc.)

A dynamic rheological method to study the interaction between starch and lipids

A.‐C. Eliasson and H.‐R. Kim

J. Rheol. 39, 1519 (1995); http://dx.doi.org/10.1122/1.550613 (16 pages)

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A dynamic rheological method was used to follow transitions occurring during heating and cooling of starch–lipid gels that were prepared separately from the rheological measurement. A decrease in storage modulus (G′) and a simultaneous increase in phase shift (δ) were interpreted as due to a transition of the amylose–lipid complex. During cooling an increase in G′ and a decrease in δ were observed. The temperature of this transition (Tm) was found to depend on the type of starch, chain length of complexing ligand, polar head group of the ligand, and salt concentration for ionic ligands. For a hydroxypropylated potato starch lower Tm values were observed than for the native potato starch. Surfactants with longer hydrocarbon chains gave higher Tm values. The polar head influenced the stability so that it increased in the following order: cationic<anionic<nonionic. For the charged ligands Tm increased with the concentration of NaCl. This was explained as due to a generic electrostatic effect of ions on the helix–coil transformation. Not only the transition of the amylose–lipid complex was affected as described. Also the rheological properties of the starch–lipid gel at room temperature were possible to change depending on the ligand used. By combining the proper starch and surfactant/emulsifier it was thus possible to obtain very strong and elastic gels (i.e., high G′ and low δ values) or very weak and viscous gels (i.e., low G′ and high δ values). © 1995 Society of Rheology
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83.60.Bc Linear viscoelasticity
83.80.Lz Physiological materials (e.g. blood, collagen, etc.)
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