ISSN:
1435-1528
Keywords:
Dilutesolution
;
concentratedsolution
;
mean configurationmodel
;
secondnormal-stress difference
;
flow hardening
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
Abstract A review is given of the “pathline” that the author followed in his search for structural constitutive models which predict viscoelastic properties. In the first section of this work an analysis was carried out of a dilute solution of rigid dumbbells, and subsequently, of linear-elastic dumbbells with finite equilibrium length. In doing so, the associated constitutive equation in the special case of Hookean dumbbells could be identified with that of an Oldroyd B fluid. The second section was devoted to the indication of conditions under which second normal-stress differences would appear. This was shown to be the case for solutions of rigid dumbbells with spheroidal beads with and without inclusion of hydrodynamic interaction and also for solutions of rigid spheroids. In the third section of this pathline attention was focused on the dependence of rheological properties of suspensions with rigid particles of different shape on orientation and motion, subject to different types of flow. Finally, in the last section an approach was attempted for comprehending more concentrated solutions. This was based on the concept of configuration-dependent tensorial mobility as a function of the mean configuration tensor. Even a linear relation between these tensors resulted in a model which predicted most features of polymer fluids. When a slightly more complicated relation of relaxation type was substituted instead, these predictions could be substantially improved. At last, inclusion of a quadratic and an exponential term, respectively, in the first mentioned linear relation allowed for a description of flow hardening phenomena. In conclusion, a new approach is made concerning shear hardening. It is derived from a paper written about 30 years ago, in which the modification of the effective flow field — owing to the action of particles — is correlated with the extra stresses resulting therefrom. In the special case of macroscopic shear flow the effective flow field is no longer a plane “weak” flow, but a spatial “strong” flow in which elastic particles, e.g. polymer coils, can be oriented and continuously stretched in a fixed position if they are slender enough. If counteracting influences, such as are described, for example, in terms of a configuration-dependent mobility, are allowed to be overcome by this effect, shear thinning will change into shear thickening and, at the same time, the second normal-stress difference will become positive. This may cause instability phenomena even in straight flows.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01329295
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