Explore chapters and articles related to this topic
Fluid Mechanics Measurements in Non-Newtonian Fluids
Published in Richard J. Goldstein, Fluid Mechanics Measurements, 2017
Christopher W. Macosko, Paulo R. Souza Mendes
For a Newtonian fluid,ηe is just 3 times the shear viscosity because T11=2με˙ and T22=−με˙. From the continuum mechanics theory, the relation ηe = 3η0 is expected to hold at low stress levels, even for non-Newtonian materials. In general, the extensional viscosity function behavior is qualitatively different from that of the shear viscosity. Frequently, polymeric solutions exhibit extensional “thickening,” while their shear viscosities are typically shear thinning (see Fig. 8.9). Other qualitative behaviors have also been reported [13, 14], and the various experimental difficulties make it nearly impossible to draw definitive conclusions about the true behavior of ηe. For example, results are confounded by the difficulty in determining whether steady extension has, in fact, been achieved during the experiment. Figure 8.10 shows results at very high extensions for a low-density polyethylene melt. We see that even at total strain of over 7 (extension ratios of 103), the steady state has not been attained.
Laboratory Techniques for Processability Testing
Published in Nicholas P. Cheremisinoff, Polymer Mixing and Extrusion Technology, 2017
The extensional viscosity is normally defined as the ratio of stress to extensional rate; that is, () ηϵ=τϵ˙
Quantifying separation energy with a modified Capillary Break-up Extensional Rheometer (CaBER) to study polymer solutions
Published in Soft Materials, 2021
Kamran Riazi, Mahdi Abbasi, Christopher O. Klein, Ingo F. C. Naue, Manfred Wilhelm
For a polymer solution, the measurement of the normal force allows the calculation of the extensional viscosity.[18,39] Under the assumption of a purely viscous behavior, the extensional rate-dependent extensional viscosity can be calculated from Equation (4), [18]