Showing papers on "Rheometer published in 1980"

Shear‐Induced Structure in a Concentrated Suspension of Solid Spheres

Abstract: Two novel phenomena were observed in steady and transient shear measurements which were made in a Couette device of a R‐17 Weissenberg Rheogoniometer with suspensions of polystyrene spheres, 40–50 μm in diameter, suspended in a mixture of silicone oils at volume fractions 0⩽φ0.55. When φ⩾0.3, the steady‐shear viscosity at a given shear rate was found to drift for many hours to an asymptotic value which, in contrast to the scatter of the initial measurements, was very reproducible. Again, when φ⩾0.3, the shear stress showed a memory for the direction of previous shearing when the shear was stopped for a while and then restarted with either the same or the opposite sign. Moreover, during oscillatory shear experiments, these suspensions exhibited a nonlinear response which in fact could be predicted from their response to a sudden reversal of the direction of steady shear. It would appear, therefore, that such concentrated two‐phase systems cannot be modeled as isotropic fluids having a scalar effective viscosity unless the solids concentration is low.

Dependence of the Elongational Behavior of Polystyrene Melts on Molecular Weight and Molecular Weight Distribution

Abstract: The elongational viscosity and the tensile compliance on four polystyrenes of different molecular weights and molecular‐weight distributions were determined by means of an extensional rheometer designed particularly for investigations on a small amount of polymer. The steady‐state elongational viscosity at small strain rates is three times the zero‐shear viscosity according to the Trouton relationship. The Trouton viscosity is proportional to Mw3.5 independent of the molecular weight distribution. For the steady‐state tensile compliance in the linear range of elongation no quantitative relationship with molecular data can be given but a strong increase of the compliance due to small amounts of a higher molecular weight component is observed. In the nonlinear range of elongation a small viscosity maximum as a function of tensile stress is observed for three samples whereas one sample shows an increase of the elongational viscosity up to values which are at least five times higher than the elongational visc...

Relation between steady shear flow and dynamic rheology

Abstract: The relationships between steady shear flow and dynamic rheology are investigated at relatively high shear rates and frequencies A useful empirical relationship in this region predicts that the magnitude of the complex dynamic viscosity |η*| should be compared with the shear viscosityη at equal values of frequency and shear rate (Cox-Merz-rule) Polystyrenes (PS) and Polyacrylamides (PAAm) have been investigated over a wide range of concentration and molecular weight Only in case of PAAm/H2O solutions we have found that the results do not coincide with Cox-Merz-rule As far as we know this is the first time that deviations from Cox-Merz-rule were observed in a homogeneous system A molecular interpretation is given

The measurement of the second normal stress difference for some polymer solutions

Abstract: The second normal stress difference N2 can be determined by measuring the free surface shape of fluids flowing down a semicircular channel. A photograph is taken of a graduated straight edge and its reflection in the fluid surface. The shape of the surface is then calculated from the shape of the straight edge reflection using geometrical optics. We show that the surface shape can be measured to an accuracy of ±0.01 mm by this photographic method, leading to a value of N2 which is accurate to about ±0.1 N m−2. A study was made of a number of moderately concentrated polymer solutions. The shear stress τ and the first nomral stress difference N1 were measured on a cone—plate rheometer while the second normal stress difference N2 was determined from the pipe flow experiment. The normal stress ratio N2/N1 was found to be negative and independent of shear rate in the range 1 < γ. < 100 s−1. The ratio N2/N1 is weakly dependent on concentration and our values are consistent with those obtained by other investigators using different methods to measure N1 and N2.

Evaluation of the flowability of melted mozzarella cheese by capillary rheometry

Abstract: Flow curves of mozzarella cheese at 30, 40, 55, and 70°C were determined by a capillary piston-driven rheometer. The shear stresses and rates were calculated using the Bagley and Rabinowitch correction formulae. The standard test and correction procedure was applicable to melted mozzarella cheese, but not to other types of cheese (notably cheddar) in which slippage and other effects played a dominant role.

The oscillating rheometer--what does it measure?

Abstract: The motion involved in the operation of an oscillating rheometer was analyzed, and revealed that the instrument measured a complex mixture of an instrument-dependent parameter, the spring constant, and two material-dependent parameters--the dynamic viscosity and the shear storage modulus. The significance of the working and setting time parameters measured by the rheometer are discussed.

A rheometer for measuring the viscoelastic response of polymer melts in arbitrary planar and biaxial extensional flow fields

Abstract: In this paper we describe the operation of a rheometer that is capable of measuring the viscoelastic response of a polymer melt in a biaxial or planar extensional flow field under circumstances wherein the deformation history can be varied in an arbitrary manner. The principal feature of this rheometer is the use of a closed loop feedback system to control the inflation of a flat, molten polymer sheet clamped around its periphery. The feedback system is especially designed so that either stress or strain can be used as the reference point, thus permitting the deformation history to be varied arbitrarily. Illustrative data are presented on the viscoelastic response of a molten acrylonitrile-butadiene-styrene copolymer subjected to a planar extensional flow for the following deformation histories: constant stress, constant strain, constant strain rate, oscillatory stress and oscillatory strain.

A Sandwich-Type Creep Rheometer for the measurement of rheological properties of polymer melts at low shear stresses*)

Abstract: A new Sandwich-Typ Creep Rheometer (SCR) is described which is suited for measuring the zero shear viscosityη 0 and the steady-state shear complianceJ e 0 of polymer melts. The range of shear stresses extends from 2 N/m2 to 5000 N/m2. Measurements down to shear rates of 10−5 s−1 and less are possible on high viscosity melts. The agreement between the SCR data and results from a modified Weissenberg rheogoniometer is shown for the viscosities as well as the compliances. Relations are presented which allow to take into account the non negligible influence of the surface tension of the sample on the measurements. From the reverse shear rate of the unloaded sample after total recoil the magnitude of the surface tension can be determined.

Time‐Dependent Behavior of Viscoelastic Suspensions

Abstract: Time‐dependent viscoelastic measurements on suspension were investigated. To characterize the structural state, an “instantaneous” viscoelastic function was used, which was obtained by Fourier transformation of the resultant stress to pulse strain of the cosine type. The experiments were made on a suspension of glass beads in a polystyrene solution using a coaxial cylinder rheometer. When the time‐scale of the measurement is comparable with that of the structural change, the measured stress for a sinusoidal strain contains the response due to the structural change besides the viscoelastic response. Therefore, a conventional dynamic method is not applicable to such time‐dependent materials. However, as the time‐scale of a pulse strain is quite different from that of the structural change, the method used provides useful information on the relaxation process during the structural change.

Stresses and Recoverable Strains of Stretched Polymer Melts and Their Prediction by Means of a Single Integral Constitutive Equation

Abstract: The elongational behaviour of various polymer melts was measured by means of an elongational rheometer using a rotating clamp1,2 The servo control makes it possible to apply varying or constant stresses or strain rates (Fig 1) The recoverable strain and the quality of the test is determined from three cut-offs

Separation of Shear Thinning and Elastic Effects in Experimental Rheology

Abstract: The development of non shear-thinning elastic fluids and their use to isolate elastic effects in experimental rheology is reviewed. On the basis of experiments conducted to date, it seems clear that it is conceptually inadequate to apply what might be called “second-order or Maxwell thinking” in the analysis of any but perhaps extensional flows. Large qualitative effects in complex flows of viscoelastic fluids are associated with deformation rate regions in which the normal stresses are not quadratic, or for the constant viscosity elastic fluids, in deformation rate regions where the shear modulus is deformation rate dependent. Experiments illustrate that in the context of slow flow expansions, fluid elasticity does not appear to be a dominant variable until “fourth order effects” are present.

Rheology of Luting Cements

Abstract: A rheometer has been developed to simulate the extrusion of luting cement from beneath a full crown during seating using clinically realistic shear rates. Five luting cements were studied, and differences in rheological behavior were illustrated. These measurements demonstrate the importance of consideration of the effects of shear rate on viscosity when evaluating a cement for optimal clinical utilization.

Rheometer and rheological measuring method

Abstract: A rheometer of the extrusion plastometer type is provided with means for forcibly mechanically mixing the material to be tested within the chamber of the rheometer. The rheometer preferably includes a pair of telescopically arranged pistons which can be selectively coupled and uncoupled from one another so that one of them can serve as a mixing device. The pistons are coupled for unitary movement when discharging the material being tested.

Oscillating rheometer die set

Abstract: An oscillating rheometer die set is disclosed, having modifications to the lower die apparatus, the upper die apparatus, and the oscillator head. The purpose of these modifications include the creation of a sealing cavity of annular nature about the oscillator head, such that the elastomer sample is not encapsulated and once cured, may be easily removed from the cavity.

Uniaxial Extensional Experiments with Large Strains Performed with Low Density Polyethylene (LDPE)

Abstract: In this paper results of three different types of extensional experiments are presented, which were performed with a new version of the Uniaxial Extensional Rheometer with rotary clamps: (A) extension with constant strain rate, (B) recovery after cessation of extension with constant strain rate, and (C) extension with constant tensile force. The LDPE used had a density at 20°C of p20 = 0.919 g/ cm3 and a melt flow index of MFI =1.37 g/10 min /1/. The test temperature was 150°C.

Uniaxial elongational viscosity at a constant strain rate of polybutene-1 melt

Abstract: The measurement of elongational viscosity of polybutene-1 melt has been carried out at a constant strain rate with an elongational rheometer which measures simultaneously the diameter of elongating samples. Non-linearity parameter of the viscosity was calculated from the total elongational viscosity values by dividing with the values of linear parts. The non-linearity parameters of the elongational viscosity were almost independent of strain rate and temperature. Four rheological constitutive models of integral type were chosen and applied for the elongational flow at a constant strain rate. The chosen models were the Lodge model, the Bogue and White model, the Bernstein, Kearsley and Zapas model, and the Wagner model. These models predicted the non-linearity of the elongational viscosity at high strain rate well. However, the non-linearity parameter predicted from these constitutive models showed strong dependences on both strain rate and temperature.

Temporary viscosity loss in shear stability testing

Abstract: The relationships between the permanent and temporary viscosity losses were examined for 43 oils at 100 degree C and 150 degree C. High-shear-rate viscosities were measured at a shear rate of 10**6 s** - **1 in a capillary viscometer for new oils and used oils. New oils that had been subjected to 20 cycles in the fuel injector shear stability test were considered to be used oils in this program.

Large Homogeneous Biaxial Extension of Polyisobutylene and Comparison with Uniaxial Behaviour

Abstract: Compared with the activity during the last decade in uniaxial extension of polymer melts, the investigation of their biaxial behaviour has been rather limited because of experimental difficulties. In a previous paper /1/, a new type of biaxial rheometer has been described, which has distinct advantages over the conventional bubble inflation technique. Using this new rheometer, equibiaxial extensional experiments on polyisobutylene at room temperature (22°C) and constant strain rates have been made. The results of these experiments are compared with the response of the same material in uniaxial extension and simple shear.

A New Research Rheometer

Abstract: Just a decade ago Rheometrics introduced the Mechanical Spectrometer.1 Sophisticated rheological measurements are now common in most large academic, industrial and government laboratories. These measurements are being made over an ever widening range of materials and test conditions. Rheologists are now beginning to push present instruments to their design limitations. One example is measurements at ultra-low shear rate. It is extremely valuable for molecular characterization to obtain limiting viscosity and normal stress coefficients for polymer melts. This often requires shear rates below 0.01 s-1. At the opposite extreme, ver fast transient measurements are needed for determination of short relaxation times and for identifying the rubbery plateau. Furthermore, not only shear but tensile deformations are required for many applications. To deal with the range of materials encountered in many laboratories much wider ranges in stress detection are required: from water-like fluids to rigid solids.

The Wall Effect in Orthogonal Stagnation Flow

Abstract: The kinematic boundary condition has a profound effect on the velocity field in a flow channel. This effect will be studied with respect to an extensional rheometer of planar extensional flow.

Contribution to the Elongational Viscosimetry of High-Polymeric Solutions

Abstract: Elongational flows play a decisive role in many shaping processes of manufacturing technology. Specific flow phenomena, by which we mean a multitude of instabilities and breaks, may definitely limit the technological possibility of controlling elongation flows, above all in the spinning of artificial fibres, the coating of film materials, and film blowing, In these processes, the rheological characterization of the behaviour of the fluid materials to be processed under elongational load is an indispensable precondition. Work on these problems is carried out in order to define the material function of elongational flow by analogy with simple shear, and to ensure exact measurement in suitable rheometer flows. At present, the rheological characterization of the elongational behaviour of highpolymeric solutions presents difficulties greater than those found in other groups of materials.

Use of Annular Flat Plates in the Modified Balance Rheometer to Measure Normal Stresses

Abstract: Various workers (Walters1, Ginn and Metzner2) have utilised torsional flow in the determination of the viscometric functions of elastic liquids.

On the Torque and Energy Balances for the Flow Between E(ccentric) R(otating) D(iscs)

Abstract: Rheometrical flow systems in which a small perturbation is superimposed on a rigid rotation have been the subject of considerable interest in recent years, both from the experimental and theoretical points of view. Yet there are some problems with respect to the flow field in these rheometers which are not satisfactorily solved. This paper will mainly deal with the orthogonal rheometer, but similar problems arise with other rheometers based on the same principle. The velocity field in ERD flow as realized in the orthogonal rheometer was first proposed by Blyler and Kurtz1. It was shown, however, that this velocity field leads to some fundamental problems. First of all there is the so-called “stress power paradox”2,3, expressing the paradoxal observation that, although energy is dissipated in the sample, no power seems to enter into it from the apparatus. In the second place it was pointed out4,5 that the total torque acting on the sample differs from zero. This led these authors to the assumption that a torsional flow was superimposed on the primarily assumed flow. Finally, the stress field resulting from the proposed flow field1, also when an additional torsional flow field is superimposed on it, does not obey the boundary conditions at the free edge. In order to overcome this latter difficulty it was assumed4 that there is an edge zone in which the flow field is not of the form postulated.

On the Rheological Behaviour of Cement Suspensions Tested in a Couette Rheometer

Abstract: The theological properties of cement suspensions are with regard to the workability of both mortars and concretes of particular significance for building technology.