摘要:

The shear viscosity material function of a highly filled suspension consisting of a Newtonian poly(butadiene acrylonitrile acrylic acid terpolymer) matrix, PBAN, mixed with an ammonium sulfate filler at 60% by volume was studied. Both capillary and parallel disk torsional flows were employed. The rheological characterization revealed strong slip of the suspension at the walls over a broad range of shear stresses in both types of flows. The slip velocity increased approximately linearly with the shear stress. In capillary flows, above a critical shear stress, flow took place in a pluglike manner, owing to slip at the wall. The experimental findings were further elucidated to determine the slip layer thickness and the apparent shear viscosity behavior of highly filled suspensions at high shear stress at the wall values. It was concluded that the slip effects dominate the flow of highly filled suspensions and the true flow and deformation characteristics of the highly filled suspensions may be overshadowed by slip at the walls.

ISSN:0148-6055    

DOI:10.1122/1.550049

出版商:The Society of Rheology    

年代:1989

数据来源: AIP

摘要:

Rheological properties of concentrated suspensions (∼70 wt%) of relatively coarse particles of crushed quartz (∼11 μm) in solutions of various metal chlorides were studied. The apparent viscosity of these settling suspensions, as measured with a “settling viscometer,” was compared with the zeta potential of the particles, the degree of aggregation, the sediment volume, and the degree of hydration of the metal cation. As the salt concentration increased and the suspensions coagulated, their viscosity increased. However, suspensions that were qualitatively completely aggregated showed large variations in apparent viscosity at100 s−1,depending on the particular metal cation of the salt solution. The viscosities increased in the orderLi

ISSN:0148-6055    

DOI:10.1122/1.550050

出版商:The Society of Rheology    

年代:1989

数据来源: AIP

摘要:

This article describes an experimental apparatus and analysis scheme for determining the viscoelastic properties of a material isothermally, with a single apparatus, over 10 decades of time and frequency. Torque was applied to the specimen electromagnetically and its deformation was determined by laser interferometry. Resonances were eliminated from the torque and angle measuring devices by this approach. Resonances remaining in the specimen itself were corrected by a numerical analysis scheme based on an analytical solution which is applicable to homogeneous cylindrical specimens of any degree of loss. The apparatus is capable of creep, constant load rate, subresonant dynamic, and resonant dynamic experiments in bending and torsion. The range of equivalent frequency for torsion is from less than10−6 Hzto about104 Hz.The capability of the apparatus is illustrated with measurements upon several viscoelastic elastomers and upon poly(methyl)methacrylate.

ISSN:0148-6055    

DOI:10.1122/1.550071

出版商:The Society of Rheology    

年代:1989

数据来源: AIP

摘要:

Recoverable strains were measured on isotropic and liquid crystalline solutions of PBLG [poly(γ‐benzyl‐L‐glutamate)] and HPC [hydroxypropylcellulose]. For isotropic PBLG, the strain recovery approaches the expected linear viscoelastic behavior in which the recovery is proportional toγ̇0,asγ̇0—the shear rate prior to recovery—becomes small. In the nonlinear regime for isotropic PBLG, the magnitude and shear‐rate dependence of the recoverable strain are qualitatively consistent with the Doi theory. In the liquid crystalline state, neither PBLG nor HPC show a regime of linear viscoelasticity even at strain rates low enough that the viscosity is nearly independent ofγ̇0.Instead, the total strain recovery is independent ofγ̇0,although the time over which this recovery occurs is inversely proportional toγ̇0.Plots of recoverable strain versus the product of timetandγ̇0for various values ofγ̇0nearly superpose. This scaling of recovery time withγ̇0−1is similar to a result obtained with PBLG by Moldenaers and Mewis and confirmed here in measurements ofG′andG″after cessation of steady‐state shearing. Remarkably, not only do plots of recovered strain versusγ̇0tfor variousγ̇0superpose for each of the three liquid crystalline PBLG and HPC samples, but even curves for the three different materials come fairly close to superposing. Extending an idea of Marrucci, a simple phenomenological scaling equation for the evolution of domain size and domain distortion is proposed that can account for these phenomena.

ISSN:0148-6055    

DOI:10.1122/1.550072

出版商:The Society of Rheology    

年代:1989

数据来源: AIP

摘要:

Linear viscoelastic dynamic moduli of two‐phase polymer blends in the molten state have been measured as a function of frequency in a conicylinder rheometer. The polymer blends are characterized by high values of the storage modulus at low frequencies and by long relaxation times. The model developed by Choi and Schowalter for semidilute emulsions of Newtonian liquids has been used to account for the variations of dynamic moduli in the terminal zone. In this frequency range, the rheological behavior is directly related to a few physically significant parameters such as zero‐shear viscosity of phases, dispersed particle size, and interfacial tension between phases. The experimental results obtained for the polydimethylsiloxane‐polyoxyethylene blends show that the variation of matrix viscosity and volume fraction of inclusions is in accordance with the semidilute emulsion law.

ISSN:0148-6055    

DOI:10.1122/1.550051

出版商:The Society of Rheology    

年代:1989

数据来源: AIP

摘要:

We extend methods from the kinetic theory of gases to obtain a general constitutive relation for the collisional source of second moment in dilute flows of identical, smooth, highly inelastic spheres. In the derivation, we base all statistical averaging on an anisotropic Maxwellian distribution function, which is sensitive to all components of the full second moment of fluctuation velocity and is not based on the assumption that the fluctuations are nearly isotropic. In the case of homogeneous shear flow, we combine the constitutive relation with the balance equation for full second moment to determine, for prescribed values of shear rate, coefficient of restitution, and solid fraction, both exact numerical and approximate closed‐form solutions for the second moment and pressure tensor. Most striking are the resulting normal pressure differences, which are predicted by this theory but not by kinetic theories for nearly elastic particles.

ISSN:0148-6055    

DOI:10.1122/1.550052

出版商:The Society of Rheology    

年代:1989

数据来源: AIP

摘要:

Streamline finite‐element results are presented for the extrudate swell of a high density polyethylene (HDPE) melt flowing through straight, converging, and diverging annular dies. Viscometric data have been fitted using a spectrum of relaxation times and the K‐BKZ integral constitutive equation. For the elongational viscosity a reasonable strain‐thinning behavior has been assumed. Numerical calculations for three die designs show the dependence of diameter and thickness swell on the taper angle. It is found that the K‐BKZ equation is capable of capturing memory phenomena exhibited by polymer melts in such geometries, which are in sharp contrast with Newtonian or Maxwell fluid simulations. The present results show that the diameter swell is highest for the converging, followed by the straight and then the diverging dies, in qualitative agreement with experimental findings available in the literature. While the simulations for converging and diverging annular dies failed to converge at high flow rates, converged results were obtained for straight annular dies at high flow rates (very high shear rates on the wall upstream), and the predictions for the diameter swell are in satisfactory agreement with experimental data.

ISSN:0148-6055    

DOI:10.1122/1.550053

出版商:The Society of Rheology    

年代:1989

数据来源: AIP

摘要:

Drawing of liquid filaments from a circular die is the most successful method to date for determining the response of polymer solutions in uniaxial extension. Reported here is an analysis of the experimental uncertainties in fiber‐drawing extensional rheometry and the effect they have on the results. In fiber drawing, measurements of the liquid flowrate, the variation of the fiber diameter along its length, and the force exerted on the die are used to determine the extension rate and the corresponding extensional stress. Experimental uncertainty in the flowrate measurement ordinarily is of little consequence, but the same is not true of the uncertainties in the diameter profile and the force measurement. The optical measurement of the diameter profile is limited by diffraction and chromatic aberration. The precision of the force measurement is limited by uncertainty in the nulling procedure. In addition, competition among contending forces limits the operating range of reliable extensional measurements. At low stress levels (∼103dynes/cm2), inertial, gravitational, and surface tension forces dominate over viscous forces and destroy the precision of the extensional stress measurement. At high stress levels (∼106dynes/cm2), cavitation may be limiting. The magnitude of the gravity force determines minimum attainable extension rates (∼10 s−1) whereas instabilities limit the maximum ones. These operating limits are supported by experiments on glycerine and solutions of several water‐soluble polymers; polyacrylamide, hydroxymethylcellulose, xanthan, and guar.

ISSN:0148-6055    

DOI:10.1122/1.550009

出版商:The Society of Rheology    

年代:1989

数据来源: AIP

摘要:

A series of polybutadienes(78,000⩽MW⩽240,000),each with a narrow molecular weight distribution (MW/MN<1.1), was extruded through slit capillary dies. Signals from a pressure traducer and from hot‐film anemometers embedded in the capillary wall were used to infer the behavior of the polymer at the wall. Although slip flow was not observed for polymers withMW=78,000over the range of flow rates available, the higher molecular weight species showed a pattern of no‐slip, alternate sticking and slipping, and slip flow as the flow rate was increased. Slip velocities were estimated using a three‐dimensional model of heat transfer from the hot‐film probe. In the stick‐slip regime, there is a distinct asymmetry between the process of breakdown of continuity at (or very near) the wall, and the re‐establishment of a no‐slip boundary condition.

ISSN:0148-6055    

DOI:10.1122/1.550073

出版商:The Society of Rheology    

年代:1989

数据来源: AIP