摘要:

Rheological theory including volume (compressible) effects is important in a practical sense in that many polymer processes involve rapid cooling to a final, typically nonequilibrium, glassy state. There are also compressible effects in the sense of Poisson's ratio—that is, deformation‐induced volume changes occur even at constant temperature. In earlier work we (Snow and Bogue) set down a generalized constitutive equation which includes these various effects. The integral statement there is quite complicated, however, and is difficult to execute except in the simplest deformations. The present work is a restatement of the prior formulation in a more tractable and slightly modified form.

ISSN:0148-6055    

DOI:10.1122/1.549932

出版商:The Society of Rheology    

年代:1987

数据来源: AIP

摘要:

The transient flow of mayonnaise is described by a three‐parameter model which is a slight modification of a model developed by Larson for polymer melts with wide molecular weight distribution. It is demonstrated that despite the fact that the model has only three parameters it gives a very reasonable description of the stress overshoot phenomenon with respect to both the stress magnitude and the time at which the peak stress is reached. It is also shown that the damping constant, presumably a shear rate‐independent parameter, is in reality a weak function of the latter. Since the fit of the stress‐time curve is not highly sensitive to the magnitude of the damping parameter this difficulty can be overcome by using a mean value over the pertinent range of rates.

ISSN:0148-6055    

DOI:10.1122/1.549931

出版商:The Society of Rheology    

年代:1987

数据来源: AIP

摘要:

Dilute solutions of polyethylene oxide (PEO) and polyacrylamide (PAM) were subjected to shearing and then extensional motion in order to determine the influence of prior shear on the extensional resistance of these fluids. The work was originally motivated by the explanation of drag reduction by polymer additives and so the tests were conducted in a flow cell designed to simulate the ejection event (burst) in a turbulent boundary layer flow. The results show that prior shear had a considerable effect on the PEO solutions, causing significant extensional resistance at strain rates of order102 s−1,while rates one order higher were necessary to generate an extensional effect when there was no prior shear. For the PAM solutions, on the other hand, extensional resistance depended only weakly on prior shear, and onset strain rates and resistance magnitudes depended more markedly on the ionic strength of the solvent. Tests with NaCl andCaCl2in the solvent identicated that Na and Ca ions affect the extension of PAM molecules in different ways. A flow visualization study revealed that the flow patterns for water and PEO solutions were the same but those for PAM solutions were always unsteady.

ISSN:0148-6055    

DOI:10.1122/1.549933

出版商:The Society of Rheology    

年代:1987

数据来源: AIP

摘要:

This paper presents the effects of liquid polarity on the rheology of suspensions with particle sizes ranging from 2 to 150 μm. We have found that liquid polarity has a substantial effect on the non‐Newtonian behavior of suspensions of graphite particles, but only a slight effect on that of polystyrene suspensions. This may be attributed to the greater interparticular van der Waals‐London dispersion force for graphite than for polystyrene. The suspensions of polystyrene spheres become Newtonian at very high shear rates when the interparticular van der Waals force is negligible as compared to the hydrodynamic force. This high shear Newtonian limit of relative viscosity is in excellent agreement with the value predicted by the rigid sphere model for colloidal suspensions.

ISSN:0148-6055    

DOI:10.1122/1.549934

出版商:The Society of Rheology    

年代:1987

数据来源: AIP

摘要:

All versions of the internal viscosity (IV) model for polymer chain dynamics lead to the prediction that the inception of flow from a rest state is accompanied by a stress jump att=0.For the general case of long chains (large number of submolecules,N), the jump is predicted here for the onsets of simple shear flow and elongational flow at constant deformational rate. The exact model formulation (i.e., following Booij and van Wiechen) is used, without the need to approximate deformational velocities in the Cerf/Peterlin sense, and rigorous closed‐form solutions are presented. This is apparently the only rheological prediction now available for the largeNIV model using the rigorous formulation. Intermediate steps in the analysis demonstrate the extent to which the motions of beads are correlated with those of neighbors at various distances in the linear sequence; the effect is small and depends slightly onφ/f.Final results show that viscosity jumps are independent of deformational rate and depend on both φ andφ/f,where φ is the IV coefficient andfthe bead/solvent friction coefficient. Experiments on stress jumps and subsequent transients are thus potentially able to evaluate φ alone, unlike steady‐state experiments which respond only toφ/f.Predictions for shear flow are also compared with those made using the Cerf/Peterlin linearization approximation, showing that the two diverge severely at high values ofφ/f.

ISSN:0148-6055    

DOI:10.1122/1.549949

出版商:The Society of Rheology    

年代:1987

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.549960

出版商:The Society of Rheology    

年代:1987

数据来源: AIP