Highly elastic polymer solutions under shear: Polymer migration, viscoelastic instabilities, and anomalous rheology
- Univ. of California, Berkeley, CA (United States)
The use of highly elastic polymer solutions has been remarkably successful in elucidating the behavior of polymeric materials under flowing conditions. Here, we present the results of an extensive experimental study into the shear behavior of an athermal, dilute, binary polymer solution that is believed to be free of many of these effects. Under extended shearing, we observe the migration of polymer species: after shearing for several hundred hours, concentrations that are more than double the initial uniform value can be achieved. Although the solutions are well-described by dumbbell models in shear flows on short-time scales, theoretical predictions substantially underestimate the rate of migration. Flow visualization and rheometric experiments suggest that the origin of this discrepancy could be the anomalous long-time rheology of these solutions. While these fluids display the well-known elastic instability in cone and plate flow above a critical Deborah number, extended shearing reveals that the toroidal secondary flow is eventually replaced by a purely azimuthal shearing flow. In addition, when sheared below the critical condition for the instability, the solutions exhibit a slow but reversible decay in normal stresses. The shear-induced migration of polymer species has been predicted by numerous theoretical studies. However, observations on the highly elastic polymer solutions that are most likely to show polymer migration, are complicated by a number of different physical processes that occur as a result of shearing. These phenomena, which include shear-induced phase separation, elastically-induced hydrodynamic instabilities, mixed solvent effects, shear-induced aggregation, and anomalous transient shear and normal stress behavior are often observed at times earlier than and at shear rates less than those where migration is predicted to occur; hence, the experimental detection of polymer migration has been thwarted by these other physical processes.
- OSTI ID:
- 602928
- Report Number(s):
- CONF-961108-; TRN: 98:001968-0063
- Resource Relation:
- Conference: Annual meeting of the American Institute of Chemical Engineers (AIChE), Chicago, IL (United States), 10-15 Nov 1996; Other Information: PBD: 1996; Related Information: Is Part Of 1996 First joint topical conference on processing, structure and properties of polymeric materials; PB: 594 p.
- Country of Publication:
- United States
- Language:
- English
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