Showing papers on "Rheology published in 1993"
TL;DR: The properties of aqueous solutions of model HEUR associative thickeners under dynamic and steady shear have been studied as a function of concentration, molecular weight, temperature, and hydrophobic end-cap length as discussed by the authors.
Abstract: The properties of aqueous solutions of model HEUR associative thickeners under dynamic and steady shear have been studied as a function of concentration, molecular weight, temperature, and hydrophobic end‐cap length. It is shown that solutions of AT behave as near perfect Maxwell fluids inasmuch that Cole–Cole plots of the dynamic moduli are almost exactly semi‐circular. An Arrhenius law temperature dependence of the static viscosity and relaxation time is also observed, providing confirmation of a single relaxation process. In certain other respects, AT solutions show more complex behavior, e.g., the Cox–Merz rule is not obeyed, with the steady shear viscosity showing a weaker dependence on shear rate than does the complex viscosity upon frequency. Furthermore, weak shear thickening is seen to precede shear thinning in steady shear. The above results are consistent with the predictions of a transient network theory presented recently by Tanaka and Edwards and Jenkins (generalized Green–Tobolsky theory). ...
710 citations
TL;DR: In this paper, a filament stretching device for measuring the extensional viscosity of low-viscosity liquids is presented, where the fluid sample is held between two disks which move apart at an increasing velocity so that the extension rate, based on the filament midpoint diameter, is constant.
Abstract: A filament stretching device for measuring the extensional viscosity of low‐viscosity liquids is presented. The fluid sample is held between two disks which move apart at an increasing velocity so that the extension rate, based on the filament midpoint diameter, is constant. The device was used to measure the extensional stress growth coefficients of three ideal elastic solutions, including the model fluid M1 and a shear‐thinning model fluid A1. The results indicate that all solutions containing high molecular weight polymer exhibit significant strain hardening as the fluid is extended. For the ideal elastic fluids, steady state in extensional stress was observed at strain above 4.5 and the steady Trouton ratio obtained for the fluids range from 2 to 5×103. For the fluid M1 the extensional viscosities obtained are higher than the apparent extensional viscosity obtained by other methods. This is the first time that the steady extensional viscosity has been measured for polymer solutions. The results obtain...
314 citations
TL;DR: In this article, nonequilibrium molecular dynamics computer simulations of a planar Couette flow are presented for the multibead anharmonic-spring model, where the finitely extensible nonlinear elastic force law is used to connect the up to 100 beads of a chain molecule.
Abstract: Results of nonequilibrium molecular dynamics computer simulations of a planar Couette flow are presented for the multibead anharmonic‐spring model. The finitely extensible nonlinear elastic force law is used to connect the up to 100 beads of a chain molecule. Rheological data (shear viscosity, normal pressure differences) are discussed and compared with quantities describing the chain conformation (e.g., alignment tensor, static structure factor). This renders possible a test of the theoretical approaches which connect these quantities. In agreement with recent experiments, the static strucure factor exhibits characteristic elliptical distortions of the polymer coil whose magnitude depends on the distance from the gyration center. In our simulations the zero‐shear‐rate viscosity is found to scale linearly with the number of beads N up to chains with N=60. A weak upturn of the viscosity per bead for N=100 is found which may indicate the onset of the reptation regime.
209 citations
194 citations
TL;DR: In this article, the rheological behavior of a very concentrated liquid rocket fuel simulant was characterized employing both torsional and capillary flows, with the slip velocity increasing from about 0.001 mm/s at a shear stress of 4 Pa to as high as 60 mm/m at 100 kPa.
Abstract: The rheological behavior of a very concentrated suspension (76.5 vol %), which serves as a widely used solid rocket fuel simulant, was characterized employing both torsional and capillary flows. No comprehensive studies of the rheology of concentrated suspensions have been carried out previously at such a high solids content. The suspension exhibited shear thinning over the apparent shear rate range of 30–3000 s−1. Significant slip at the wall was observed in both torsional and capillary flows with the slip velocity increasing from about 0.001 mm/s at a shear stress of 4 Pa to as high as 60 mm/s at 100 kPa. A flow visualization technique was applied for the first time to determine the wall slip velocities in torsional flow directly, to also provide the true deformation rate and feedback on yielding. The contribution of the slip of the suspension at the wall to the volumetric flow rate in capillary flow was found to increase with decreasing shear stress, giving rise to plug flow at sufficiently low shear s...
192 citations
TL;DR: The rheological behaviour of lyotropic lamellar phases is studied as a function of the membrane repeating distance and three distinct regions of different orientations are described, which are separated by two out-of-equilibrium transitions.
Abstract: The rheological behaviour of lyotropic lamellar phases is studied as a function of the membrane repeating distance. The steady-state rheology is described as a consequence of the so-called orientation diagram described previously. Three distinct regions of different orientations are described, which are separated by two out-of-equilibrium transitions. We show that these transitions can be either discontinuous (subcritical) or continuous. In one of these transitions, one can go continuously from one regime to the other through a bifurcation point.
172 citations
TL;DR: In this article, a new theoretical approach based on qualitative microstructural physics and thermodynamical arguments is developed which considers flow, elastic deformations, ruptures and restorations of flocs.
Abstract: The objective of this paper is to provide a complete theoretical and experimental study of shear rheology for concentrated dispersed systems in low molecular weight matrices. A new theoretical approach based on qualitative microstructural physics and thermodynamical arguments is devel- oped which considers flow, elastic deformations, ruptures and restorations of flocs. The approach was developed to study steady and transient phenomena and has predicted very different behaviours for various systems; one of them was a non-monotonic flow curve. The most remarkable feature of the theoretical model is that it contains no mathematical yield criterion but predicts anisotropic yield values with continuous transition from solid state to flow as a bifurcation. A complete set of experiments in simple shearing was carried out for two different dispersed systems: a granular grease and a water-clay platelet mixture. Also some disturbing phenomena were observed and experimental techniques were developed which made it possible to obtain reliable results. Additionally the clay-water system exhibited a minimum in the flow curve, and all the characteristics peculiar to the evolution from solid state to flow, as predicted by the theory. Despite the short time scale of transition phenomena for the materials tested, the general comparison of experimental results with theory showed good agreement.
163 citations
TL;DR: In this article, the particle-particle and particle-solvent interactions of fumed silica with hydrophilic and hydrophobic surface groups dispersed in both polar and nonpolar solvents, polypropylene glycol and mineral oil, respectively, were examined.
Abstract: Fumed silica suspensions in low molecular weight solvents are used in many photonic and microelectronic applications. The rheology of these thixotropic systems plays a major role in the effectiveness of their usage. In this study, we use dynamic rheological measurements to examine the particle–particle and particle–solvent interactions of fumed silica with hydrophilic and hydrophobic surface groups dispersed in both polar and nonpolar solvents, polypropylene glycol and mineral oil, respectively. We find the mineral oil‐based suspensions to have a frequency‐independent elastic modulus (G’) for all solids concentration, whereas the polypropylene glycol‐based systems exhibit a ‘‘sol–gel’’ transition to a frequency‐independent G’ at high concentrations. The results are explained in terms of different solvent particle mechanisms present in the two systems. The behavior of the mineral oil suspensions are dominated by particle–particle interactions through hydrogen bonds, resulting in a gel structure. The polypr...
155 citations
TL;DR: The Motion of Bubbles And Drops In Reduced Gravity Fluid Particles In rheologically complex media the motion of a sphere through an elastic fluid the effects of surfactants on flow and mass transport to drops and bubbles rate of gas absorption by liquids and "surface resistance" shapes of fluid particles.
Abstract: The Motion Of Bubbles And Drops In Reduced Gravity Fluid Particles In rheologically complex media the motion of a sphere through an elastic fluid the effects of surfactants on flow and mass transport to drops and bubbles rate of gas absorption by liquids and "surface resistance" shapes of fluid particles - flow of particles in viscoelastic fluids rheology of filled polymeric systems simulation of particle deposition in fluid flow.
150 citations
TL;DR: In this article, a finite element method based on a primitive variables formulation is used to model both steady-state and time-dependent mantle convection with a composite Newtonian and non-Newtonian (power-law) rheology.
Abstract: Summary
A finite element method based on a primitive variables formulation is used to model both steady-state and time-dependent mantle convection with a composite Newtonian and non-Newtonian (power-law) rheology. The rheological model employs the transition stress as a means of partitioning the relative importance of the two rheologies. Results show that there is no direct correlation between viscosity and temperature anomalies. Fluctuations of the velocity fields are much greater and faster than for Newtonian flows. Fluctuations with amplitudes several times the background velocity are quite common. Intermittency effects with quiescent periods punctuated by chaotic bursts are observed. From scaling arguments temporal fluctuations of the volume-averaged viscosity are comparable in magnitude to the variations in the surface heat flow for the non-Newtonian flows, but are smaller than the variations in the velocity field. At larger transition stress the Newtonian behaviour becomes dominant and the temporal variations of the viscosity diminish. Both steady-state and time-dependent results show that for a given transition stress the non-Newtonian behaviour prevails to a greater extent with increasing Rayleigh number. Implications of this non-Newtonian tendency for Archaean tectonics are discussed.
TL;DR: In this article, a common surfactant solution system is investigated to demonstrate the characteristic and generic features observed in shear-thickening self-assembling fluids, and it is shown that shearinduced coagulation results in selfassembling of surfactants to form new micelles which are of exceedingly large sizes and which can survive against th...
Abstract: A common surfactant solution system is investigated to demonstrate the characteristic and generic features observed in shear‐thickening self‐assembling fluids. Rheological and flow birefringence measurements on the aqueous CTAB/sodium‐salicylate solutions disclose a number of unusual flow behaviors under different flow conditions. All solutions with concentrations ranging from 0.5 to 5 mM exhibit shear thickening above certain critical shear rates, accompanied by an increase in flow birefringence over a range of temperature from T=14 to 36 °C. An extraordinarily long induction period, which is found to be inversely proportional to the applied shear rate, precedes the establishment of the shear‐thickening state. This dynamic state is highly flow birefringent, strongly nonlinear viscoelastic and possesses long relaxation times. We deduce that shear‐induced coagulation results in self‐assembling of surfactant molecules to form new micelles which are of exceedingly large sizes and which can survive against th...
Journal Article•
TL;DR: In this article, Lucassen-Reynders et al. reviewed background and existing data on the rheology of interfaces and indicated how rheological paramete rs can be estimated in areas where measurements are difficult.
TL;DR: In this paper, the authors show that the general hydrophobicity of the polymers' end groups control both rheology and efficiency, and that the hydrophobic parts in the interior of the polymer do not seem to effect rheological in latex systems.
Abstract: Nonionic associative thickeners with systematic changes in chemical composition have been synthesized. Rheological measurements of thickened latexes are presented as well as measurements of relaxation times, intrinsic viscosity and osmotic pressure of polymers in pure water solution. We find that the general hydrophobicity of the polymers' end groups control both rheology and efficiency. Hydrophobic parts in the interior of the polymer do not seem to effect rheology in latex systems. Viscosity increases with molecular weight in the low molecular region (Mw<10000), and passes through a maximum in the high molecular region. The thickeners seem to form micelle-like aggregates even at very low concentrations, while at higher concentrations the viscoelastic properties may be modeled by means of one Maxwell element. Only the network relaxation times but not the network structure seems to be dependent on the polymers' end group.
TL;DR: In this paper, the dynamic oscillatory response of electrorheological suspensions is investigated using a molecular dynamics-like simulation method, where suspensions are modeled as hard, monodisperse, neutrally buoyant, dielectric spheres contained in a dielectrics, Newtonian fluid between parallel plate electrodes.
Abstract: The dynamic oscillatory response of electrorheological suspensions is investigated using a molecular dynamics‐like simulation method, where suspensions are modeled as hard, monodisperse, neutrally buoyant, dielectric spheres contained in a dielectric, Newtonian fluid between parallel‐plate electrodes. The response is described by frequency‐dependent moduli, which display a significant relaxation due to competition between hydrodynamic and electrostatic forces on spheres within thick clusters. For small amplitude deformation of monodisperse suspensions, the direct electrostatic contribution to the response obeys time‐electric field strength superposition analogous to time–temperature superposition in polymer rheology. The response for monodisperse suspensions is dominated by a single relaxation time, in contrast to the broad dispersions commonly observed. Possible explanations for this discrepancy are discussed.
TL;DR: In this article, the authors measured the shear viscosity and the first and second normal stress coefficients for several solutions made from nearly monodisperse polystyrenes and found that the dependence of the first normal stress difference on dimensionless shear rate is similar to the prediction of beads-and-springs theories.
Abstract: The shear viscosity and the first and second normal stress coefficients, are measured for several solutions made from nearly monodisperse polystyrenes. The molecular weights and concentrations of the solution components were chosen to that molecular theories could be tested in three different regimes: dilute, semidilute entangled, and concentrated unentangled. It is found for dilute solutions that the dependence of the first normal stress difference on dimensionless shear rate, or Weissenberg number Wi, is similar to the prediction of beads-and-springs theories and that Ψ, the negative of the ratio of the second to the first normal stress difference, is near zero, as predicted
TL;DR: In this article, Pulsed gradient spin-echo Fourier transform NMR (PGSE-FT NMR) and rheology measurements on aqueous solutions of these polymers reveal a distribution of self-diffusion coefficients that broadens continuously with increasing concentration.
Abstract: Nonionic associative polymers have been produced by hydrophobically modifying poly(oxyethylene) with hydrophobic end group straight hydrocarbon chain length varying from 8 to 18 carbon atoms. Pulsed gradient spin-echo Fourier transform NMR (PGSE-FT NMR) and rheology measurements on aqueous solutions of these polymers reveal a distribution of self-diffusion coefficients that broadens continuously with increasing concentration. The distribution is described by a stretched exponential from which mean diffusion coefficients are extracted. The concentration dependences of these diffusion coefficients are described by the stretched exponential of Phillies
01 Jan 1993
TL;DR: A critical appraisal of available methods for the measurement of extensional properties of mobile systems is given in this article, where a parsimonious model for viscoelastic liquids and solids is presented.
Abstract: Preface. Contraction flows and new theories for estimating extensional viscosity. A critical appraisal of available methods for the measurement of extensional properties of mobile systems. Surface rheology. Large-amplitude oscillatory shear. A parsimonious model for viscoelastic liquids and solids. Rheological studies using a vibrating probe method. Dynamic mechanical analysis using complex waveforms. Rheological measurements in small samples. Rate- or stress-controlled rheometry. Rheometry for process control. Index.
TL;DR: In this article, the influence of shear thinning and viscoelasticity on the power required for the mixing of viscous liquids using six different helical ribbon agitators has been investigated.
Abstract: The influence of shear thinning and viscoelasticity on the power required for the mixing of viscous liquids using six different helical ribbon agitators has been investigated. Four Newtonian and 12 non-Newtonian fluids prepared using several polymers dissolved in varying concentrations in different solvents cover a wide range of rheological properties. By a careful choice of test media, the specific and combined effects of shear thinning and viscoelasticity on the power requirement have been examined. Simple models are proposed to predict the effective shear rate in the tank from the knowledge of the torque or power number. The effective shear rate predictions compared with the effective shear rate estimated using the scheme of Metzner and Otto (1957) show that they slightly depend on the shear thinning properties. Fluid's elasticity increases appreciably the power requirement, and departures from the generalized Newtonian power curve in the laminar regime are observed at smaller Reynolds numbers for viscoelastic fluids. Bottom wall resistance of the mixing vessel makes a negligible contribution to the power consumption.
TL;DR: In this paper, the effect of bubble-free and vesicular rhyolite melts containing spherical voids of 10 and 30 vol % on the frequency-dependent rheology of the material was investigated.
Abstract: Frequency dependent rheology of magmas may result from the presence of inclusions (bubbles, crystals) in the melt and/or from viscoelastic behavior of the melt itself. With the addition of deformable inclusions to a melt possessing viscoelastic properties one might expect changes in the relaxation spectrum of the shear stresses of the material (e.g., broadening of the relaxation spectrum) resulting from the viscously deformable geometry of the second phase. We have begun to investigate the effect of bubbles on the frequency dependent rheology of rhyolite melt. The present study deals with the rheology of bubble-free and vesicular rhyolite melts containing spherical voids of 10 and 30 vol %. We used a sinusoidal torsion deformation device. Vesicular rhyolite melts were generated by the melting (at 1 bar) of an Armenian obsidian (Dry Fountain, Erevan, Armenia) and Little Glass Mountain obsidian (California). The real and imaginary parts of shear viscosity and shear modulus have been determined in a frequency range of 0.005–10 Hz and temperature range of 600°–900°C. The relaxed shear viscosities of samples obtained at low frequencies and high temperatures compare well with data previously obtained by parallel plate viscometry. The relaxed shear viscosity of vesicular rhyolites decreases progressively with increasing bubble content. The relaxation spectrum for rhyolite melt without bubbles has an asymmetric form and fits an extended exponent relaxation. The presence of deformable bubbles results in an imaginary component of the shear modulus that becomes more symmetrical and extends into the low-frequency/high-temperature range. The internal friction Q −1 is unaffected in the high-frequency/low-temperature range by the presence of bubbles and depends on the bubble content in the high-temperature/low-frequency range. The present work, in combination with the previous study of Stein and Spera (1992), illustrates that magma viscosity can either increase or decrease with bubble content, depending upon the rate of style of strain during magmatic flow.
TL;DR: High viscosity in plant cell culture is therefore not an intrinsic characteristic of plant cells but, instead, is a result of the ability to grow cultures to extremely high cell densities due to low biological oxygen demand.
Abstract: The results of rheological measurements on 10 different plant cell suspension cultures are presented. Nicotiana tabacum (tobacco) suspension cultures grown in serial batch subculture display high viscosity and power law rheology. This "undesirable" rheology is shown to be a result of elongated cell morphology. The rheology of Papaver somniferum (poppy) cell suspensions is quite different; poppy suspensions behave as Newtonian fluids and have relatively low viscosity (less than 15 cP) at fresh cell densities up to 250 g/L. This flow behavior can be attributed to a lack of elongation in batch-grown poppy cells. A simple correlation for the viscosity as a function of cell density is developed for poppy suspensions up to 300 g fresh weight (FW)/L. It is shown that tobacco cells do not elongate when grown in semicontinuous culture (daily media replacement). These semicontinuously cultured cells have rheological behavior that is indistinguishable from that of poppy, further confirming the dependence of rheology on plant cell morphology. The rheology of a wide variety of other plant suspensions at 200 g FW/L is presented. Most cell suspensions, including soybean, cotton, bindweed, and potato, display low viscosities similar to poppy suspensions. Only carrot and atriplex exhibit slight pseudoplastic behavior which corresponded to a slight degree of cellular elongation for these cultures. This demonstrates that complex rheology associated with elongated cell morphology is much less common than low-viscosity Newtonian behavior. High viscosity in plant cell culture is therefore not an intrinsic characteristic of plant cells but, instead, is a result of the ability to grow cultures to extremely high cell densities due to low biological oxygen demand.
TL;DR: Oral viscosity plays an important role in the textural appreciation of fluid and semi-solid foods and small-deformation measurements have the highest correlation with assessed thickness of texture but there is still much speculation as to what forces actually operate in the mouth.
TL;DR: In this article, the effect of the changing microstructure during the flow of fiber suspensions on the flow kinematics is studied, and the governing equations for the flow field and fiber orientation are simultaneously solved in an axisymmetric radial-flow configuration.
Abstract: The effect of the changing microstructure during the flow of fiber suspensions on the flow kinematics is studied. The suspension is assumed to consist of rigid cylindrical particles immersed in a highly viscous Newtonian fluid. Further, the suspension is modeled as an anisotropic fluid whose rheological properties are functions of the local microstructure. The effect of inertia is neglected during the flow of the suspension. The orientation of the particles is assumed to be governed by the flow field and the fiber—fiber interactions. The governing equations for the flow field and fiber orientation are coupled and are simultaneously solved in an axisymmetric radial-flow configuration. These solutions are compared to those obtained using the conventional decoupled approximation where the bulk flow field is assumed to be unaffected by the presence of the suspended particles.
TL;DR: In this article, the effect of pH level, ionic strength, and temperature on the stability and stability of attapulgite clay suspensions was investigated using a Rheometrics Mechanical Spectrometer with cone and plate fixtures.
Abstract: The effect of pH level, ionic strength, and temperature on the theology and stability of aqueous suspensions of attapulgite clay was systematically investigated. A Rheometrics Mechanical Spectrometer with cone and plate fixtures was used to measure the steady shear viscosity of the system. The edge charges of the clay particles can be adjusted by changing the pH level of the suspending medium so as to influence the flocculation state and, consequently, the rheological behavior of the suspension. This pH effect may be counteracted by the ionic strength effect at both very high and very low pH levels where the ionic strength is high enough to cause flocculation of the electrostatically stabilized suspension. The temperature effect study indicates that the relative contribution of Brownian motion and shear flow to the viscosity is dependent on the flocculation state of the suspension.
TL;DR: In this article, a review of industrial applications of dispersions has been discussed and some specific topics have been covered, such as the control of the properties of the dispersions was described in terms of the interaction forces between the particles or droplets in the system.
TL;DR: In this paper, an idealized model of a porous rock consisting of a bundle of capillary tubes whose cross-sections are regular polygons is used to assess the importance of viscous coupling or lubrication during simultaneous oil-water flow.
Abstract: An idealized model of a porous rock consisting of a bundle of capillary tubes whose cross-sections are regular polygons is used to assess the importance of viscous coupling or lubrication during simultaneous oil-water flow. Fluids are nonuniformly distributed over tubes of different characteristic dimension because of the requirements of capillary equilibrium and the effect of interfacial viscosity at oil-water interfaces is considered. With these assumptions, we find that the importance of viscous coupling depends on the rheology of the oil-water interface. Where the interfacial shear viscosity is zero, viscous coupling leading to a dependence of oil relative permeability on oil-water viscosity ratio for viscosity ratios greater than one is important for a range of pore cross-section shapes and pore size distributions. For nonzero interfacial shear viscosity, viscous coupling is reduced. Using values reported in the literature for crude oil-brine systems, we find no viscous coupling.
TL;DR: In this article, it was shown for the first time that highly filled suspensions of noncolloidal particles can also exhibit a static yield stress σs, with viscoelastic solid-like behavior exhibited below σ s and visco-elastic liquid-like behaviour above σS. The dependence of this static yield stresses on the volume concentration filler is examined in this work.
Abstract: Many previous investigations have established and/or quantified yield stresses in suspensions of interacting (colloidal or surface active) particles. In this work it is shown for the first time that highly filled suspensions of noncolloidal particles can also exhibit a static yield stress σs. The determination of static yield stresses in these systems was made possible by conducting very long time (up to 6000 h) tensile creep tests. These tests are particularly suitable for high viscosity systems such as the suspensions examined here and also have the advantage that there is minimal influence on the results due to the measurement apparatus. Through these experiments, it is possible to observe an unambigious change of material response above and below the static yield stress σs, with viscoelastic solid‐like behavior exhibited below σs, and viscoelastic liquid‐like behavior above σs. The dependence of this static yield stress on the volume concentration filler is examined in this work.