Showing papers on "Rheology published in 1985"
TL;DR: In this article, the flow behavior of concentrated suspensions is reviewed for the processing of composites and similar polymeric materials, and the state of the art is a good one: a small number of experiments on a new formulation frequently suffice for a general prediction of flow behavior when solids are suspended in viscous molten polymers and in many instances, even a priori predictions of the viscosity are possible.
Abstract: This paper reviews the flow behavior of concentrated suspensions as may be of interest in the processing of composites and similar polymeric materials. Succinct synopses are arranged at the end of each section. In general, the state of the art is a good one: a small number of experiments on a new formulation frequently suffice for a general prediction of flow behavior when solids are suspended in viscous molten polymers, and in many instances, even a priori predictions of the viscosity are possible. Less viscous systems are much more difficult; several remaining problems and research areas are identified.
583 citations
TL;DR: In this paper, the Stokesian dynamics is used to investigate the rheological behavior of concentrated suspensions in a simple shear flow, and the simulation results suggest that the suspension viscosity becomes infinite at the percolation-like threshold ϕm owing to the formation of an infinite cluster.
Abstract: The newly developed simulation method known as Stokesian dynamics is used to investigate the rheological behaviour of concentrated suspensions. Both the detailed microstructure (e.g. pair-distribution function) and the macroscopic properties are determined for a suspension of identical rigid spherical particles in a simple shear flow. The suspended particles interact through both hydrodynamic and non-hydrodynamic forces. For suspensions with purely hydrodynamic forces, the increase in the suspension viscosity with volume fraction ϕ is shown to be caused by particle clustering. The cluster formation results from the lubrication forces, and the simulations of a monolayer of spheres show a scaling law for the cluster size: lc ∼ [1 − (ϕ/ϕm)½]−1, where ϕm is the maximum volume fraction that can shear homogeneously. The simulation results suggest that the suspension viscosity becomes infinite at the percolation-like threshold ϕm owing to the formation of an infinite cluster. The predicted simulation viscosities are in very good agreement with experiment. A suspension with short-range repulsive interparticle forces is also studied, and is seen to have a non-Newtonian rheology. Normal-stress differences arise owing to the anisotropic local structure created by the interparticle forces. The repulsive forces also reduce particle clustering, and as a result the suspension is shear-thickening.
519 citations
272 citations
TL;DR: In this article, the authors propose a method to solve the problem of "uniformity" and "unweighting" in the literature.Page 7.1.1]
Abstract: Page
140 citations
TL;DR: In this paper, coal was ground and wet-sieved to prepare three powder stocks whose particle-size distributions were characterized, and three suspending fluids were used (glycerin, bromonaphthalene, Aroclor), with viscosities that differed by a factor of 100 and with very different chemistries, but whose densities matched that of the coal.
Abstract: Illinois coal was ground and wet-sieved to prepare three powder stocks whose particle-size distributions were characterized. Three suspending fluids were used (glycerin, bromonaphthalene, Aroclor), with viscositiesη
s that differed by a factor of 100 and with very different chemistries, but whose densities matched that of the coal. Suspensions were prepared under vacuum, with coal volume fractionsφ that ranged up to 0.46. Viscosities were measured in a cone-and-plate over a shear rate
$$(\dot \gamma )$$
range 10−3−102 s−1. Reduced viscosityη
r = η/ηs is correlated in the high-shear limit (η
∞) withφ/φ
M∞, whereφ
M∞ is the maximum packing fraction for the high-shear microstructure, to reveal the roles of size distribution and suspending fluid character. A new model that invokes the stress-dependence ofφ
M is found to correlateη
r well under non-Newtonian conditions with simultaneous prediction of yield stress at sufficiently highφ; a critical result is that stress and not
$$\dot \gamma $$
governs the microstructure and rheology. Numerous experimental anomalies provide insight into suspension behavior.
107 citations
TL;DR: In this paper, a theoretical model is proposed to describe the non-Newtonian behavior of flocculated suspensions, which is supposed to originate from the immobilized fluid between the particles which forms flocs.
Abstract: A theoretical model is proposed to describe the non-Newtonian behaviour of flocculated suspensions. This behaviour is supposed to originate from the immobilized fluid between the particles which forms flocs. A self-consistent field approximation is used to estimate the mean radius of flowing flocs in a simple shear field, and, as a consequence, the amount of immobilized fluid in flocs. Then a rheological law is proposed in which four fixed physical parameters are involved.
106 citations
TL;DR: In this article, an experimental study on the time-dependent rheology of highly concentrated and flocculated suspensions of bauxite residue (red mud) is presented, where both the yield stress and the apparent viscosity of the material can be drastically reduced, by orders of magnitude, by shear-induced agitation with a simple anchor impeller.
Abstract: An experimental study on the time-dependent rheology of highly concentrated and flocculated suspensions of bauxite residue (red mud) is presented. Both the thixotropic breakdown with shear and recovery at rest have been quantitatively examined using a vane-shear instrument and a capillary rheometer. It is demonstrated that both the yield stress and the apparent viscosity of the material can be drastically reduced, by orders of magnitude, by shear-induced agitation with a simple anchor impeller. The rate of thixotropic decay is a function of solids concentration, agitation time and speed. With prolonged agitation, the flow properties are brought to an equilibrium level characterized by a finite yield stress and a shear rate-dependent (shear-thinning) viscosity. In the absence of shear, the yield stress gradually increases with time but at a rate considerably slower than the rate of decay in the shear field. Even after an extended rest period of several months, only a fraction of the initial yield stress can be regained. The observed behaviour has been interpreted in terms of a time-dependent but non-reversible transformation of a network structure of flocculated particles initially developed in the red mud. Using a structural kinetic approach, models have been developed for correlating the experimental kinetic data. The paper concludes with a discussion on the practical consequences of the work.
106 citations
TL;DR: In this article, a review of recent experimental work on the macroscopic rheological properties of suspensions of rod-like particles in Newtonian and non-Newtonian fluids is reviewed.
Abstract: Recent experimental work on the macroscopic rheological properties of suspensions of rodlike particles in Newtonian and non-Newtonian fluids is reviewed. Correlations are proposed for the shear viscosity-shear rate relationship for semi-concentrated and concentrated suspensions. In the former case, shear thinning behavior is found with the slope of the power law region depending upon fiber aspect ratio. For the concen trated systems, the data are substantially independent of volume fraction and aspect ratio and show slight shear thinning.
86 citations
TL;DR: The Experimental Tectonics Laboratory at Queen's University is equipped with a large-capacity centrifuge that is capable of subjecting tectonic models measuring 127 × 76 mm in plan and up to 51 mm in depth to accelerations as high as 20,000 g.
85 citations
TL;DR: In this article, the role played by transient rheology in the interpretation of mantle viscosity is reexamined by comparing the amplitude responses with the data of secular variation of J(2), the relative sea-level histories at sites well within the ice margins and at the ice margin like the city of Boston.
Abstract: The role played by transient rheology in the interpretation of mantle viscosity is reexamined. The investigation has been carried out by comparing the amplitude responses with the data of secular variation of J(2), the relative sea-level histories at sites well within the ice margins and at the ice margin like the city of Boston. A linear Burgers body rheology has been assumed in ther lower mantle. The data near the edge of the ice load proves most sensitive to the transient viscosity structure. The non-monotonic behavior of sea-level data near Boston can be explained both by a steady-state lower mantle viscosity of 10 to the 22nd P with a thick lithosphere and by a transient lower mantle rheology but with a thin lithosphere. The long-term viscosity of the lower mantle in this second model has a steady-state value of around 5 x 10 to the 23rd P.
76 citations
TL;DR: In this paper, a phenomenological model to account for low-shear-rate region of shear thinning of viscosity is presented, accompanied by lack of net orientation and by a dependence of texture and rheology on shear history.
Abstract: Liquid-crystal polymers often exhibit a low-shear-rate region of shear thinning of viscosity, accompanied by lack of net orientation and by a dependence of texture and rheology on shear history. A phenomenological model to account for this region is presented. The model uses Marrucci's description of stable domains whose size is a function of stress. The interaction of these domains is estimated from the continuum theory of liquid crystals. The shear-rate-dependent viscosity and normal stress of the polydomain fluid are calculated from the interaction energy and size of the domain by analogy with non-equilibrium molecular-dynamics calculations for small-molecule fluids. The shear-rate dependences are similar to those observed experimentally. Other tests of the model, including optical observations and measurement of dynamic viscosity, are proposed.
TL;DR: A review of polymer-melt rheology can be found in this article, where the authors present a number of methods for modeling the nonlinear rheological behavior of polymer melts.
Abstract: The rheological properties of polymers in the molten state are important for polymer engineering and science for the following reasons: (a) they depend sensitively on the chemical structure of the individual macromolecules and, therefore, are of interest for polymer characterization; (b) they are required for the development of a realistic fluid dynamics of polymer melts as the basis for any theory of polymer processing; and (c) they are responsible for large molecular orientations that are formed in the melt during processing and frozen into the final products. There they create the inhomogeneous anisotropy of all physical quantities and alter the technological end-use properties. In spite of this relevance, the central problem of polymer-melt rheology is not yet solved, viz. the formulation of a workable and correct constitutive equation that describes the stress at any instant for any deformation history. For monographs concerning this subject, see Lodge ( 1964,1974), Truesdell & Noll (1965), Astarita & Maffucci (1974), Bird et al. (1977a,b), and Janeschitz-Kriegl ( 1983). The difficulties are due to the complicated, nonlinear rheological behavior of polymer melts. These melts are not only highly viscous liquids, but in addition they are pseudoplastic (viscosity decreases with increasing shear rate) and viscoelastic (mechanical response is timeand frequency dependent), and their viscous flow is often connected with large, rubberlike elastic deformations. Furthermore, polymer melts can be elongated remarkably without rupture. In the following, methods of polymer-melt rheometry are reviewed and discussed. Most of these methods originated in the plastics and rubber industry or were transferred from other areas, like the methods of linear
TL;DR: In this article, an empirical equation which correlates the relative viscosities of emulsions (both oil-in-water and water-inoil) as a function of normalized dispersed phase concentration is proposed.
TL;DR: In this paper, the authors measured the apparent viscosity and primary normal stress difference for dispersions of fumed silica in poly(dimethylsiloxane) and found that the shape of the hysteresis loops were sensitive to the details of the deformation history.
Abstract: The apparent viscosity and primary normal stress difference were measured for dispersions of fumed silica in poly(dimethylsiloxane). Dispersions with less than 4.75% by weight of filler exhibit hysteresis in both the viscosity and normal stress, when the shear rate was increased and then decreased in discrete steps. The shape of the hysteresis loops were sensitive to the details of the deformation history. By using the appropriate deformation history, the material properties determined during the increasing shear rate part of the hysteresis experiment compare favourably with the steady-state rheological properties. The rheological properties of the dispersion were quite sensitive to the age of the fluid with no hysteresis behaviou exhibited by dispersions less than three days old. For dispersions with at least 4.75% by weight of fumed silica, neither the apparent viscosity nor the primary normal stress coefficient exhibited significant hysteresis behaviour. The relationship between the observed rheological behaviour and the dispersion's microstructure is discussed.
TL;DR: In this article, the food dough viscosity is investigated under extrusion conditions and this is then related to the product (maize grits) properties, and the shear and temperature history is simulated by using long slit dies.
Abstract: The food dough viscosity is investigated under extrusion conditions and this is then related to the product (maize grits) properties. The shear and temperature history is simulated by using long slit dies.
TL;DR: In fetal blood the higher hematocrit and the presence of larger red cells, which cause impaired passage through pores < 5 μm, are counterbalanced by a decreased plasma viscosity, resulting in a whole blood viscosities comparable to that of adults.
Abstract: Rheological parameters were measured in 10 pairs of mothers and newborns. Whole blood viscosity was similar despite a higher fetal hematocrit (47.0 ± 5.1 versus 35.5 ± 12.0%, mean ± SD, p < 0.05). When the hematocrit of the suspension of red cells in plasma was adjusted to 45%, the viscosity was significantly lower in the fetal blood over a wide range of shear rates (0.52-208 s-1). The main reason for the lower viscosity in the fetal blood was the lower plasma viscosity as compared to the maternal blood (1.08 ± 0.05 versus 1.37 ± 0.08 centipoise, p < 0.05); this in turn was attributable to a lower total plasma protein concentration (4.74 ± 0.71 versus 6.47 ± 0.64 g/dl, p < 0.05). All protein fractions were lower in the fetal plasma. The assessment of red cell deformability by filtration through polycarbonate sieves revealed that the resistance of a fetal red cell was three times higher than that of a maternal red cell in a 2.6-μm pore, but there was no significant difference in resistance for these red cells in 6.9-μm pores. This higher filtration resistance of fetal red cells through the small pores was mainly due to their large volume (115.4 ± 10.8 versus 93.5 ± 5.9 fl, p < 0.001). Measurements on membrane-free hemoglobin solutions indicated that the internal viscosity of these two types of red cells was not different. We conclude that in fetal blood the higher hematocrit and the presence of larger red cells, which cause impaired passage through pores < 5 μm, are counterbalanced by a decreased plasma viscosity, resulting in a whole blood viscosity comparable to that of adults.
Journal Article•
TL;DR: Krog et al. as discussed by the authors investigated the structure of spray-dried whipped emulsions (toppings) containing different types of lipid surfactants using the freeze-fracture technique.
TL;DR: In this article, the dynamic and transient rheological properties of a low density polyethylene melt and a plasticized polyvinylchloride melt filled with glass beads were measured at 200 °C and 180 °C respectively in a modified Weissenberg Rheogoniometer R-17.
Abstract: The dynamic and transient rheological properties of a low density polyethylene melt and a plasticized polyvinylchloride melt filled with glass beads were measured at 200 °C and 180 °C respectively in a modified Weissenberg Rheogoniometer R-17. Its main modification consisted of the use of a piezoelectric transducer instead of the conventional torsion bar, and of the interfacing of a microcomputer Apple II plus to the Rheogoniometer for data acquisition and analysis. The glass beads were pretreated with silane and titanate coupling agents to observe the effect of the chemical modification of the polymer filler interface on these properties. It was observed that both the dynamic viscosity and the storage modulus increased with the weight fraction, but this last parameter did appreciably affect the stress growth and stress relaxation curves of the polymeric matrices at low shear rates. The effect of coupling agents on these properties was varied.
TL;DR: In this paper, the effect of ionic strength (0.1 M ≤ [Cl] ≤ 0.4M), pH (3.0 ≤ pH≤ 5.0) and shear rate (up to 1000 sec−1) on the rheological response of concentrated chitosan solutions have been studied.
Abstract: The effect of ionic strength (0.1 M ≤ [Cl] ≤0.4M), pH (3.0 ≤ pH≤ 5.0) and shear rate (up to 1000 sec−1) on the rheological response of concentrated chitosan solutions have been studied. It has been observed that viscosity increases with increasing chitosan concentration and that a shear thinning behavior is present for polymer concentrations above 0.50 g/dl. Also, it has been shown that the zero shear viscosity is independent of the ionic strength of the media, but increases as pH is increased. This behavior has been related to the role of the surface charge density on the chitosan backbone upon the intermolecular entanglement which control the rheological behavior of concentrated chitosan solutions.
TL;DR: In this article, a specially designed high-shear-rate rheometer was developed, by which the rheology of polymer melts for shear rates up to 108 s−1 can be investigated.
Abstract: Little is known of the rheology of polymer melts in the high shear rate up to 106 s−1 or more. A specially designed high-shear-rate rheometer was developed, by which the rheology of polymer melts for shear rates up to 108 s−1 can be investigated. Two non-Newtonian regions and a transition or the second Newtonian region were observed in the wide range of shear rates up to 107 s−1. The observed flow curves for various polymer melts are classified into three typical patterns. One is the flow curve typically shown of high-density polyethylene in which a clear second Newtonian region appears after the first non-Newtonian region. The second is the typical flow curve of polystyrene in which a “transition region” appears instead of the second non-Newtonian region. The third is the flow curve shown of acrylonitrile-styrene copolymer, which exhibits behavior between the two types. A generalized flow curve is proposed to explain the observed flow behaviors of various polymers over a wide range of shear rates. The flow behavior in high shear rate results from high orientation and scission of polymer molecules.
TL;DR: It is demonstrated with hot film anemometry that aortic flow instabilities downstream from a temporary partial occlusion are dampened after infusion of a polymer drag-reducing agent, Separan AP-30 (Dow Chemical Co.).
TL;DR: In this article, a steady viscosity model, including both volume fraction and shear rate variables, is shown to be applicable to a large class of complex liquids which can be considered as highly concentrated disperse media.
Abstract: A steady viscosity model, including both volume fraction and shear rate variables, is shown to be applicable to a large class of complex liquids which can be considered as highly concentrated disperse media. The effect of yield stress is taken into account. For unsteady measurements, this model, which includes thixotropy, can be simply extended to viscoelastic behaviour. Some examples of application will be given, specially to heavy crude oil emulsions.
TL;DR: In this article, Gent and Lindley showed that the true stress σ versus strain plots (strain being defined as e=(h 0−h)/h) were independent of the initial height h 0.
Abstract: Experimental measurements of the response of starch gels in uniaxial compression, under both lubricated and bonded conditions, are reported. With samples of initial height h0 it was found for lubricated compression that true stress σ versus strain plots (strain being defined as e=(h0−h)/h) were independent of h0. The curves of true stress versus strain, for uniaxial compression of gels bonded to the instrument platens, lay well above the curve obtained in lubricated compression; and furthermore, the results in bonded compression were strongly dependent on h0. To a good approximation the results in bonded compression could be brought into agreement with the lubricated compression data by correcting true stress for bonded compression by a factor (1+R02/2h2)−1, a modification of a result originally reported by Gent and Lindley. The corrected curves for bonded compression were independent of h0 and agreed with the response of the lubricated samples until near the failure point. Corrected stress for bonded com...
TL;DR: In this article, a transient network model for concentrated dispersions is used to describe the rheological behavior of dispersions of glyceryl tristearate crystals in paraffin oil, and the model prediction of the storage modulus of this system is compared with corresponding expressions given in literature.
Abstract: The transient-network model for concentrated dispersions, described in a previous paper, is used to describe the rheological behaviour of dispersions of glyceryl tristearate crystals in paraffin oil. The model prediction of the storage modulus of this system is compared with corresponding expressions given in literature. Model calculations are carried out to fit the linear viscoelastic behaviour of the system as well as its stress response in large amplitude shear experiments. Information is thus obtained about the stiffness and strength of the interparticle bonds, and the chance of them breaking in a state of rest or as the result of flow. It is concluded that the probability of interparticle bond fracture strongly depends on the measure of bond stretching. The general findings link up with the Lennard-Jones potential which is assumed to describe the potential energy of the bonds between the particles. Accurate measurements of the temperature dependence of the dynamic moduli by making use of a torsion resonator lead to the conclusion that the energy dissipation at a high frequency originates mainly from the flow of liquid around the particles.
TL;DR: The application of a simple commercially available apparatus to the measurement of the dynamic shear modulus for viscoelastic food dispersions and gels is described and causes minimal mechanical disturbance to a gel or dispersion and is thus ideally suited for monitoring weak network structures.
Abstract: The application of a simple commercially available apparatus to the measurement of the dynamic shear modulus for viscoelastic food dispersions and gels is described. For vibrant gels the shear modulus can be determined to a precision of ±5% in the range 50 to 5 × 105 Nm−2 and the value is independent of the frequency as the gel behaves like a simple elastic solid. The measurement causes minimal mechanical disturbance to a gel or dispersion and is thus ideally suited for monitoring weak network structures. With weak or “dead” gels, or pastes, the dynamic modulus at just one frequency, 200 Hz, is found.