摘要:

Die swell was measured in an isothermal chamber for a series of well‐characterized polystyrene samples of differing molecular weight and molecular weight distribution (MWD). The data were organized around Tanner's die swell theory, which calls for a knowledge of the first normal stress function(N1),the shear stress function (σ), and an elastic modulus function (G). Independent rheogoniometric data forN1and σ and certain assumptions aboutGwere introduced. Many of the die swell data could be explained but large differences were noted for samples with an appreciable low‐molecular‐weight component; these small molecules seem to “lubricate” the swelling process and allow the “potential” die swell stored by the larger molecules to show itself. Also, the low shear asymptote for the die swell, usually reported to be about 1.1, was found to depend significantly on MWD. The independent rheogoniometric data showed distinct trends with MWD, with the exponent inN1=A σbvarying from about 1.8 for narrowly distributed samples to about 1.4–1.6 for broadly distributed ones. These effects can be explained by combining a quadratic blending law with a viscoelastic constitutive equation.

ISSN:0148-6055    

DOI:10.1122/1.549516

出版商:The Society of Rheology    

年代:1979

数据来源: AIP

摘要:

Experimental data are presented for the flow of dilute and concentrated aqueous solutions of polyacrylamide through porous media. For the dilute solutions, an anomalous viscosity effect is reported. In order to examine the stress field in the porous medium, series of flow visualization experiments were performed describing two‐dimensional flow through groups of cylinders for both Newtonian and non‐Newtonian fluids. The differences in flow pattern were analyzed. From our results the dominating factor in the flow through porous media appears to be the presence of elongational stresses. As a conjecture, a simple modified expression of Darcy's Law which describes the data is presented.

ISSN:0148-6055    

DOI:10.1122/1.549537

出版商:The Society of Rheology    

年代:1979

数据来源: AIP

摘要:

In a previous publication from this laboratory, the Rouse‐Bueche‐Zimm molecular theory of viscoelasticity has been extended by using a transient network model to apply to monodisperse polymers with chain entanglements. Effects of the entanglements were modeled both by the enhanced frictional coefficients and by the additional elastic couplings resulting from the transient entanglement network. For binary blends consisting of two monodisperse polymers with different molecular weights, additional modifications are now required to predict their linear viscoelastic behavior. It is recognized that entanglements not only may form between chains of the same length, but also between those of different lengths. For the latter case, the longer chain will in fact have the frictional coefficient of the shorter chain at the point of entanglement. The frequency of such interactions is assumed to be proportional to the weight ratio of the respective component chains in the blend. Equations of motion are formulated for each component and solved numerically for the relaxation spectra. Linear viscoelastic parameters such as the dynamic mechanical moduli, stress relaxation moduli, and zero shear viscosity can then be computed for the blends by linear summation of those of the components. The reduced steady state shear compliance of the blends can also be computed from knowledge of the component relaxation times. Results are found to be in excellent agreement with literature data on polystyrene, poly(dimethyl siloxane), and poly(methyl methacrylate).

ISSN:0148-6055    

DOI:10.1122/1.549517

出版商:The Society of Rheology    

年代:1979

数据来源: AIP

摘要:

Nonlinear effects in flows consisting of a viscometric part and an in‐line oscillation of finite amplitude have been studied. Shear stress measurements were made using a Weissenberg rheogoniometer model R.18 with the cone‐and‐plate geometry attached to a computerized data acquisition and analysis system. Time‐dependent shear stresses of frequencies that are both odd and even multiples of the driving motion and decreases (up to 25%) from the viscometric value of the steady shear stresses were observed using a 4.3 g/dl aqueous polyethylene‐oxide solution and the National Bureau of Standards nonlinear test sample No. 1. Measurements of the amplitude and phase of the second harmonic were obtained and related to material properties using derived formulas. Data are also presented showing the dependence upon frequency and shear rate of the material property governing the change in the steady shear stresses due to the superimposed oscillation. It was found that predictions of measured quantities based upon simple‐fluid theory were realized within experimental error. Also, comparisons of the data with predictions based on (1) the Oldroyd 4‐constant model and (2) a suspension of nearly spherical particles indicate that certain qualitative features of the data are predicted by these models.

ISSN:0148-6055    

DOI:10.1122/1.549518

出版商:The Society of Rheology    

年代:1979

数据来源: AIP

摘要:

The analytic solution to a forced and transient viscoelastic vibrating reed is found in series form. The effect of rotary inertia in addition to gravity is studied. An error analysis is performed to evaluate the effect on the computed complex modulus of errors in measured physical quantities. This error analysis includes tables over the usual testing range for use in evaluating the method of testing using half‐power bandwidth and resonant frequency.

ISSN:0148-6055    

DOI:10.1122/1.549519

出版商:The Society of Rheology    

年代:1979

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.549538

出版商:The Society of Rheology    

年代:1979

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.549539

出版商:The Society of Rheology    

年代:1979

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.549520

出版商:The Society of Rheology    

年代:1979

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.549549

出版商:The Society of Rheology    

年代:1979

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.549551

出版商:The Society of Rheology    

年代:1979

数据来源: AIP