Showing papers on "Rheometer published in 1988"

Foam Rheology: III. Measurement of Shear Flow Properties

Abstract: The experimental study of foam is complicated by its inherently unstable nature and by the presence of a liquid film slip layer at the wall. A method is described for generating reproducible and stable foam capable of retaining its structure for prolonged times. An experimental technique has also been devised which eliminates problems associated with wall slippage and allows measurement of material functions without use of any empiricisms for the wall region. In a steady‐shear flow, foam behaves like a Bingham plastic with a viscosity inversely proportional to shear rate indicating the presence of a yield stress τ0. The value of the viscosity, which is significantly higher than the parent liquid viscosity, is an increasing function of gas volume fraction φ. Yield stress values obtained by extrapolating viscosity versus shear stress data agree with direct τ0 measurements obtained by using a stress relaxation technique. The yield stress is also found to increase with φ. Small amplitude oscillatory shearing ...

On the use of flow through a contraction in estimating the extensional viscosity of mobile polymer solutions

Abstract: We consider the use of pressure measurements in contraction flows in the determination of the extensional viscosity behaviour of polymer solutions. The experimental data are interpreted on the basis of the recent theory of Binding. The resulting extensional viscosities are compared with those obtained from a commercial Spin Line Rheometer. We conclude that contraction flows provide a convenient means of determining the extensional viscosity of shear-thinning polymer solutions. The case is not so clear for constant viscosity Boger fluids. In the course of the experiments, it is shown that excess pressure losses in the contractions can be brought about by two distinct flow mechanisms in the case of Boger fluids. In the axisymmetric case, both vortex enhancement and excess pressure loss are observed, although there is not a strict one-to-one correlation between these phenomena. In the planar case, vortex enhancement is not conspicuously present, although there is still a substantial excess pressure loss at high flow rates. This excess must be associated with the ‘bulb’ flow field which essentially replaces the vortex-enhancement regime of the axisymmetric case.

A transition occurring in ideal elastic liquids during shear flow

Abstract: Dilute solutions of high molecular weight polyisobutylene dissolved in kerosene and low molecular weight polybutene have previously been reported to behave as ideal elastic liquids (“Boger fluids”). We report here rheological properties for similar solutions, having, however, higher molecular weights for the polyisobutylene. At low shear rates, these solutions exhibit the expected Boger-type rheological behavior, and approximately obey the Oldroyd-B constitutive equation. However, above a critical shear rate that depends upon molecular weight, prolonged shearing in a cone-and-plate or parallel-plate rheometer induces a time-dependent increase in the solution viscosity and elasticity. We find that the dependence of this transition on the Weissenberg number and the gap width or cone angle is consistent with a viscoelastic instability predicted by Phan-Thien for Oldroyd-B fluids. This instability appears to be of some generality for Boger fluids, since we have also observed it in a new monodisperse Boger fluid (polystyrene in low molecular weight polystyrene and dioctyl phthalate). Furthermore, this transition may have previously been observed (though not identified) by Jackson et al., using the Boger fluid polyacrylamide in maltose.

Microheterogeneity of actin gels formed under controlled linear shear.

Abstract: The diffusion coefficients and fluorescence polarization properties of actin subjected to a known shear have been determined both during and after polymerization, using a modification of a cone-plate Wells-Brookfield rheometer that allows monitoring of samples with an epifluorescence microscope. Fluorescence polarization and fluorescence photobleaching recovery experiments using rhodamine-labeled actin as a tracer showed that under conditions of low shear (shear rates of 0.05 s-1), a spatial heterogeneity of polymerized actin was observed with respect to fluorescence intensity and the diffusion coefficients with actin mobility becoming quite variable in different regions of the sample. In addition, complex changes in fluorescence polarization were noted after stopping the shear. Actin filaments of controlled length were obtained using plasma gelsolin (gelsolin/actin molar ratios of 1:50 to 1:300). At ratios of 1:50, neither spatial heterogeneity nor changes in polarization were observed on subjecting the polymerized actin to shear. At ratios of approximately 1:100, a decrease on the intensity of fluorescence polarization occurs on stopping the shear. Longer filaments exhibit spatial micro-heterogeneity and complex changes in fluorescence polarization. In addition, at ratios of 1:100 or 1:300, the diffusion coefficient decreases as the total applied shear increased. This behavior is interpreted as bundling of filaments aligned under shear. We also find that the F-actin translational diffusion coefficients decrease as the total applied shear increases (shear rates between 0.05 and 12.66 s-1), as expected for a cumulative process. When chicken gizzard filamin was added to gelsolin-actin filaments (at filamin/actin molar ratios of 1:300 to 1:10), a similar decrease in the diffusion coefficients was observed for unsheared samples. Spatial microheterogeneity might be related to the effects of the shear field in the alignment of filaments, and the balance between a three-dimensional network and a microheterogeneous system (containing bundles or anisotropic phases) appears related to both shear and the presence of actin-binding proteins.

Rheological properties, extrudate swell, and die entry extrusion flow marker experiments for rubber–carbon black compounds

Abstract: Rheological characterization, extrudate swell measurements, and a flow marker extrusion study for several elastomers and their compounds is reported. The materials included natural rubber (NR), styrene–butadiene rubber (SBR), ethylene–propylene terpolymer (EPDM), and polychloroprene (CR) and their carbon black compounds. The shear viscosity was measured with a sandwich rheometer, a shearing disk viscometer, and a capillary rheometer over a wide range of shear rates. Evidence for yield values is found in compounds with 0.20 and 0.30 levels of carbon black. Empirical equations were fit to the data. Extrudate swell measurements were carried out for slit and capillary dies. Increasing the level of carbon black reduces the level of swell. Flow marker experiments were carried out in the barrel of a capillary rheometer using a wide range of die designs. These indicated roughly radial streamline flows into the capillary or slit land. Recessed parts of a die could accumulate stagnant material. Evidence for wall slippage in the rheometer barrel for compounds with 0.20 and 0.30 volume fractions of carbon black is discussed.

Formation of a Banded Texture in Solutions of Liquid Crystalline Polymers: 1. Hydroxypropylcellulose in H2O

Abstract: The formation of a banded texture was investigated for sheared anisotropic solutions of hydroxypropylcellulose (HPC) in H2O. A cone and plate rheometer made of highly polished glass allowed the exploration of the shear rate (γ) range between 0.1 and 150 sec−1 and the study of the effect of shear time ts. Texture, monitored with a video-camera, appeared after a time tb following cessation of shear. tb is usually a decreasing function of γ and ts. In most cases a precursor banded texture precedes the banded texture, and tb attains zero at high enough γ or ts. However, when a particularly good orientation of the flowing solution is achieved, the precursor texture is not observed, tb is finite, and the bands are particularly well formed. We speculate that bands are the normal relaxation mode for well oriented solution. For less oriented solutions flow instability may lead to bands even during flow.

The concept of a rotational rheometer with helical screw impeller

Abstract: The paper is concerned with the development of an on-line rheometer for suspensions with settling particles. A new concept of a rotational rheometer with helical screw impeller is discussed. On the basis of model considerations a procedure for the flow curve determination of the investigated fluid has been proposed. Contrary to previous attempts, in the developed procedure no calibration of the instrument is necessary. The preliminary experimental verification of the developed approach proved its applicability.

Viscoelasticity of crosslinked fracturing fluids and proppant transport

Abstract: In hydraulic fracturing treatments, the success of the treatment strongly depends on the proper placement of proppant particles in the fracture. ''Proper placement'' means the packing of the fracture to achieve maximum conductivity of gas/oil through the fracture into the wellbore. The placement of the proppants along the fracture is based on design equations where sand transport velocity is related to the rheological parameters of the fracturing fluid and characteristics of the proppant particle, such as size and density. The present work describes the theoretical transport equations that take into account the elasticity of the fluid in predicting proppant settling rate in the fracture. It presents the rheological data of commonly used fracturing fluids (titanate and borate crosslinked), including viscous and elastic parameter measurements made with a Rheometrics Pressure Rheometer (RPR) and Rheometrics Mechanical Spectrometer (RMS-800). These data show some important differences between borate crosslinked gels and titanate crosslinked gels. The paper also presents experimental data of proppant settling rates in various fracturing fluids and how these can be correlated with rheological parameters obtained in this work. The difference in rheology between borate and titanate gels was correlated with the difference in settling rates of proppants in these two gels.more » The theoretical and experimental work presented here led to the conclusion that the model for proppant placement in a hydraulic fracture should include: (1) proppant characteristics, (2) viscous rheological parameters (KAPPA and n), (3) elastic parameters (complex dynamic viscosity) from linear viscoelastic constitutive equation, and (4) normal stress difference from nonlinear viscoelastic constitutive equation. The influence of crosslinked-polymer-gel network structure on proppant transport is also discussed.« less

Mechanical and rheological properties of carbon black filled polyethylene

Abstract: The mechanical and rheological properties of high density polyethylene filled with carbon black have been examined. Two sources of carbon black (one commercial and other obtained from a pyrolysis process) and various treatments have been studied. The rheological measurements in the melt state has been performed on a Rheometrics stress rheometer and a capillary rheometer. These materials possess outstanding hardness and toughness showing great potential for structural application. Comparison of carbon black from two sources showed that the carbon from the pyrolysis process has a good potential as a reinforcing agent. It was found that surface treatment reduces the particle-particle interactions and improves the filler dispersion. The relationship between the yield stresses, filler percentage, surface modification by the coupling agents and mechanical properties is discussed.

Fiber spinning of very dilute solutions of polyacrylamide in water

Abstract: The extensional viscometer developed earlier by the authors was refined and used to extend very dilute (50 ppm) solutions of polyacrylamide in distilled water. A slender liquid filament was stretched by the use of a suction device, and this resulted in the spinning of the fiber. By varying the volumetric flow rate and the filament length, stretch rates in the 100–1000 s −1 range were easily obtained. The corresponding tensile stresses were very large, and these gave apparent extensional viscosities of the order of 200 P (20 Pa s). In contrast to this, the material functions in shear were difficult to measure, except for the shear viscosity which showed pronounced shear thinning. It was found that all the measurements, in shear as well as extension, could be explained based on the four constant Johnson-Segalman constitutive equation.

Magnetically driven, acoustically tracked, translating‐ball rheometer for small, opaque samples

Abstract: A new rheometer has been designed to measure the rheological properties at low Reynolds number of microliter quantities of opaque suspensions. The rheometer uses a falling‐ball technique to measure steady‐state viscosity and a vertically oscillating, magnetically driven ball for viscoelastic measurements. The motion of the ball is tracked by ultrasound echo location, in which sound waves are transmitted and received by an ultrasound transducer mounted at the base of the tube. Concentrated suspensions of red blood cells are used as opaque test samples. The results obtained are in good agreement with those reported in the literature. The data confirm the fact that a concentrated suspension of red blood cells behaves as a shear thinning material and that the energy stored by the suspension during an oscillatory cycle increases with frequency. Testing of the rheometer is also made by using a Newtonian silicone oil. Viscosity measurements obtained with both the falling‐ and oscillating‐ball methods are consist...

Small Strain, Low Shear Rate Rheometry of Cohesive Sediments

Abstract: Elastic and yield phenomena of cohesive sediments are usefully studied with pulse shearometry and an applied stress rheometer combined with vane geometry. These sediments are elastico-viscous materials at volumetric concentrations ϕ equal to or greater than the critical concentrations ϕ SF at which a space-filling network exists in the sediment. Vane geometry provides reliable estimates of yield stress (Γ y ) in fresh, undisturbed sediment. Γ y and shear rigidity modulus G are strongly dependent on ϕ.

Rheological properties of liquid crystalline solutions of ethyl celluloses with different molecular weight in m-cresol

Abstract: Steady-state shear rheological properties of liquid crystalline solutions of four ethyl celluloses (ECs) were determined at a low shear rate (1 s−1) and at relatively high shear rates by using two rheometers (cone-plate and capillary types), and were compared with those of liquid crystalline hydroxypropyl cellulose (HPC). The effect of molecular weight (MW) on the viscoelastic behavior was also determined. The viscoelastic behavior was also determined. The viscometric behavior of EC solutions was similar to that of HPC solutions: (1) with respect to temperature, the shear viscosity (η) at shear rate of 1 s−1 exhibited a minimum (ηmin) and a maximum (ηmax), and the concentration–temperature superposition for η could be applied; (2) the behavior of η at relatively high shear rates as a function of shear rate or polymer concentration was typical of lyotropic liquid crystals. The MW dependence of ηmin was greater than that of ηmax for EC solutions. The behavior of the elastic parameters such as Bagley correction factor (v), entrance pressure drop (ΔPent), and die swell (B) at relatively high shear rates for EC solutions was essentially similar to that for HPC solutions: (1) the shear rate or stress dependence of the elastic parameters was greatly dependent on whether the polymer solution was in a single phase or biphase; (2) with respect to concentration the elastic parameters showed a maximum and a minimum and the maximum or minimum point for each parameter was not always identical to each other. η for the isotropic or fully anisotropic solutions at a given concentration (C) increased, whereas η for the solutions in the vicinity of the biphasic region showed a minimum, with respect to MW. The slope of η at a given shear rate vs. CMw depended on shear rate, and this slope for the isotropic solutions appeared to be greater than that for fully anisotropic solutions. ΔPent and v at a given concentration showed either a monotonical increase or a maximum or minimum with MW, and this behavior was not fully consistent with that of η. B for the isotropic solutions increased and B's for both biphasic and fully anisotropic solutions were almost constant, with MW.

Elongational rheology of polyethylene melts — temporary network constitutive laws

Abstract: The uniaxial elongational properties of various polyethylenes have been evaluated using an elongational rheometer and a melt-strength apparatus. It is possible to derive the data obtained in elongation from the distribution of relaxation times obtained from oscillatory shearing measurements (linear viscoelasticity), using a Wagner constitutive equation. The effects of the molecular parameters of the samples have been studied, in particular the effect of polydispersity on the shape of the damping function.

New instrumentation for advanced rheometry

Abstract: A new applied-strain, general purpose research rheometer is described. The rheometer is designed to give optimum performance in viscometry, oscillation and stress relaxation tests. Combined tests such as relaxation after steady flow, oscillation after steady shearing, etc. are also possible.

Flow mechanisms in dense silica-metal oxide-water suspensions

Abstract: The rheological properties of dense silica in water suspensions (approx. 50% solids by volume) containing additions of metal oxides were examined. Metal oxides used were ferric, zinc and stannic. To prevent settling, testing was performed in a rheometer which was modified to provide for continual stirring of the materials. Relatively small oxide additions had the effect of thickening the mixtures and making them non-Newtonian. Different rate-limiting steps for flow were identified depending on the particular mixture, testing temperature and shear strain rate. Flow could be described using empirical equations which are identical to those often used to describe plastic flow in solid crystalline materials.

Interparticle bond energy and rheological properties of clay suspensions

Abstract: A new method was developed for measuring the heat released when the interparticle bonds in a clay suspension reform after being broken by a shearing stress. In this method, the rotor and cup of a Stormer viscometer were located within one of the microcalorimetric elements of a Calvet microcalorimeter. After filling the annulus between the rotor and cup with a clay suspension and establishing thermal equilibrium, a brake was released and the rotor was activated for a few seconds by a falling weight. The weight was attached to a string that was wound around a drum geared to the rotor. A stopwatch was used to measure the time of shear, i.e., the rotation time, and the microcalorimeter was used to measure the heat generated. In a related experiment, the rheological properties of the suspension were determined with a Fann viscometer. The product of shear stress, shear rate, and time of shear equals the heat dissipated by viscous flow. When the value of this product was substracted from the corresponding value fo the total heat dissipated, the result was the heat dissipated by the formation of bonds that were broken in the process of shear. We calculated an average value for the latter quantity by averaging the results obtained at various combinations of shear stress, shear rate, and time of shear. The procedure-described above was repeated for several suspensions of different clay and electrolyte concentrations. It was found that the heat of bond formation increased in magnitude as the clay concentration increased but decreased in magnitude as the electrolyte concentration increased. Also, it was found that the heat of bond formation was correlated with the extrapolated shear stress of the suspension.

Multiple Flow Regimes in the Extrusion of Nitrocellulose Based Propellant Doughs

Abstract: : Flow curves of triple, double, and single base propellant doughs were determined with an extrusion rheometer. In most cases the curves displayed an inflection which was associated with a critical stress in the dough. The critical stress caused the flow to separate into a high stress layer near the boundary of the flow, and a low stress region in the centre of the flow. The critical stress was also associated with flow instabilities. An explanation of the flow behaviour based on the Doi-Edwards theory is presented. Keywords: Australia, Rheology, Viscosity Index.

Dynamic Shear Moduli and their Relationship to Fabric of Granular Materials

Abstract: This paper presents experimental results from the investigation of the change of granular fabric during shear deformation and the determination of its relationship with the shear modulus measured at low strain amplitude. A torsional simple shear/resonant column device was used to perform experiments on hollow cylindrical specimens under a variety of stress conditions. The effects of the fabric on the shear moduli of different stress paths, stress reversals, rotations of principal stress axes, and preshearing were investigated.

A Paradigm for the Viscosity of Fluids

Abstract: A new paradigm for the viscosity of fluid is presented by considering the fact that the viscosity is equal to the shear stress divided by the shear rate. The shear stress is obtained from the sum of kinetic and internal pressures of fluid, and the shear rate is found from the phonon velocity divided by the mean free path of the phonon. The calculated viscosities for various simple substances are in excellent agreements with those of the observed data through the wide temperature range covered both of liquid and gas phase.

Dynamic and Steady State Measurements on Sealants Above and Below the Yield Point

Abstract: Sealants and caulks are used in construction situations where they are subjected to sizable deformations relative to the stress required for flow while curing and after curing. This study was designed to examine the elastic and viscous nature of specially prepared materials having built‐in variations in time‐dependent structure development. Few measurements have been made to characterize the elastic nature of the structure developed by such materials and to relate these to performance properties. When strains which exceed the elastic limit are developed, these systems can form brittle fractures. Above the elastic limit, the viscous properties of the material become dominant which should reduce the tendency to fracture. Tests were performed with the Rheometrics Mechanical Spectrometer and the Carri‐Med Controlled Stress Rheometer. The viscoelastic components (G′,G″,η*) and steady shear transient tests were obtained with the Mechanical Spectrometer. Since the Stress Rheometer induces a stress and measures a...

Measuring apparatus for rotating rheometers having a cone and a plate

Abstract: The invention relates to a measuring apparatus for rotating rheometers having a cone and a plate, between which there is a liquid to be measured, cones having various external diameters being able to be used as desired for the purposes of measurement in various viscosity ranges and/or standard stress ranges, a common plate being assigned to the cones, and the external diameter of the plate corresponding to that of the largest cone which can be used. The invention can be applied to measuring apparatuses for rotating rheometers with which viscosity measurements and/or measurements of the first and second standard stress difference in the region of the higher shear gradient can be carried out with a broad band of viscosity and standard stress values. According to the invention concentric annular grooves are worked into the flat face of the plate facing the cone, the internal diameter of the annular grooves corresponding to the external diameter of the respective assigned cone.

The Effect of Processing Variables on the 'Internal Slip Flow' of a Triple Base Gun Propellant Dough

Abstract: : The rheological behaviour of triple base gun propellant doughs of N and NQ types was measured with an extrusion rheometer at temperatures of 20C, 30C and 45C, using slit and capillary dies. The propellant doughs were made from two grades of nitrocellulose, and from picrite obtained from two sources. Acetone/water mixtures and acetone/ethanol mixtures were used as processing solvents. Most of the processing variables had little effect on flow behaviour. It as found that a type of internal slip occurred in the dough at a shear stress of about 60 kPa. and this had a significant effect on flow behaviour. Australia.

The behaviour of clay in simple shear and triaxial tests

Abstract: The main objective of this work is to study the applications of critical state soil mechanics to simple shear testing. The problems with the simple shear apparatus and the approach for interpreting simple shear test results are described. Laboratory tests were conducted using the NGI simple shear apparatus, standard shear box arid computer controlled stress path testing equipment for samples with38 mm and 100 mm diameter. The test programme comprised simple shear and shear box tests on remouled, reconstituted and undisturbed samples of Cowden till and London clay, undrained triaxial tests on reconstituted arid undisturbed London clay and stress probing tests on undisturbed London clay. Simple shear samples were tested under either constant effective vertical stress or constant volume condition. Basic results for one-dimensional compression arid for shearing obtained from 72 simple shear tests , 27 shear box tests and 16 stress path tests are presented. Analyses of the simple shear test results indicate that the critical state friction angle for horizontal planes cs' is dependent on whether the sample was sheared under constant Ov' or constant volume condition and on the pre-shearing value of K0 which is a function of overconsolidation ratio. A theory for the critical states of simple shear tests which takes into account the influence of K 0 is proposed.The normalised test data show that the overall patterns of the simple shear and triaxial tests are as predicted by the critical state model. Tangent stiffnesses instead of secant stiffnesses were calculated For simple shear tests, the shear stifTnesses obtained from constant \' shearing are the same as those obtained from constant volume shearing. For London clay, the norm alised shear moduli for undrained triaxial tests have the same order of magnitude as those for constant volume simple shear tests. Results of probing tests show that undisturbed London clay is linear anisotropic elastic. The elastic parameters for the constitutive equations can be measured from special stress paths.