Abstract
The use of constant viscosity, highly elastic polymer solutions, so called Boger fluids, has been remarkably successful in elucidating the behavior of polymeric materials under flowing conditions. However, the behavior of these fluids is still complicated by many different physical processes occurring within a narrow window of observation time and applied shear rate. In this study, we investigate the long-time shear behavior of an ideal Boger fluid: a well characterized, athermal, dilute, binary solution of high molecular weight polystyrene in oligomeric polystyrene. Rheological measurements show that under an applied steady shear flow, this family of polymer solutions undergoes a transient decay of normal stresses on a timescale much longer than the polymer molecule's relaxation time. Rheological and flow visualization results demonstrate that the observed phenomenon is not caused by polymer degradation, phase separation, viscous heating, or secondary flows from elastic instabilities. Although the timescale is much shorter than that associated with polymer migration in the same solutions (MacDonald and Muller, 1996), the appearance of this phenomenon only at the rates where migration has been observed suggests that it may be a prerequisite for observing migration. In addition, we note that through sufficient preshearing of the sample, the normal stress decrease suppresses the elastic instability. These results show that there is considerable uncertainty in choosing the appropriate measure of the fluid relaxation time for consistently modeling the critical condition for the elastic instability, the decay of normal stresses, and the migration of polymer species.
Similar content being viewed by others
References
Agarwal US, Dutta A, Mashelkar RA (1994) Migration of macromolecules under flow: the physical origin and engineering implications. Chem Eng Sci 49:1693–1717
Barham PJ, Keller A (1990) Flow-induced liquid-liquid phase separation and adsorption entanglement layer formation in high molecular weight polymer solutions. Macromolecules 23:303–309
Barham PJ, Hikmet RAM, Narh KA, Keller A (1986) Adsorption-entanglement layers in flowing high molecular weight polymer solutions. III. Solution concentration and solvent power. J Colloid Polym Sci 264:515–521
Baumert BM, Muller SJ (1995) Flow visualization of the elastic taylor-couette instability in Boger fluids. Rheol Acta 34:147–159
Boger DV, Yeow YL (1992) The impact of ideal elastic liquids in the development of non-Newtonian fluid mechanics. Exp Therm and Fluid Sci 5:633–640
Boger DV (1996) Viscoelastic fluid mechanics — interaction between prediction and experiment. Exp Therm and Fluid Sci 12:234–243
Byars JA, Öztekin A, Brown RA, McKinley GH (1994) Spiral instabilities in the flow of highly elastic fluids between rotating parallel disk. J Fluid Mech 271:173–218
Chmielewski CK, Nichols KL, Jayaraman K (1990) A comparison of the drag coefficients of spheres translating in comsyrup-based and polysyrene-based Boger fluids. J Non-Newtonian Fluid Mech 35:37–49
Doi M, Edwards SF (1986) The theory of polymer dynamics. Clarendon Press, Cambridge
Dupuis D, Lewandowski FY, Steiert P, Wolff C (1994) Shear thickening and time-dependent phenomena: the case of polyacrylamide solutions. J Non-Newtonian Fluid Mech 54:11–32
Larson RG (1991) Instabilities in viscoelastic flows. Rheol Acta 31:213–263
Larson RG (1992) Flow-induced mixing, demixing and phase transitions in polymeric fluids. Rheol Acta 31:497–520
Laufer Z, Jalink HL, Staverman AJ (1973) Time dependence of shear and normal stresses of polystyrene and poly (ethylene oxide) solutions. J Poly Sci Poly Chem Ed 11:3005–3015
MacDonald MJ, Mullet SJ (1996) Experimental study of shear-induced migration of polymers in dilute solutions. J Rheol 40:259–283
Magda JJ, Larson RG (1988) A transition occurring in ideal elastic liquids during shearing flow. J Non-Newtonian Fluid Mech 30:1–19
Magda JJ, Lee CS, Muller SJ, Larson RG (1993) Rheology, flow instabilities, and shear-induced diffusion in polystyrene solutions. Macromolecules 26:1696–1706
Mani S, Malone MF, Winter HH (1992) Shear-induced demixing in a polystyrene/poly (vinyl methyl ether) Blend: In-situ fluorescence and rheometry. Macromolecules 25:5671–5676
McKinley GH, Öztekin A, Byars JA, Brown RA (1995) Self-similar spiral instabilities in elastic flows between a cone and a plate. J Fluid Mech 285:123–164
McKinley GH, Byars JA, Brown RA, Armstrong RC (1991) Observation on the elastic instability in cone-and-plate and parallel-plate flows of a polyisobutylene Boger fluid. J Non-Newtonian Fluid Mech 40:201–229
Niemiec JM, Pesce JJ, McKenna GB, Skocypec S, Garritano RF (1996) Anomalies in the normal force measurements when using a force rebalance transducer. J Rheol 40:323–334
Öztekin A, Brown RB (1993) Instability of a viscoelastic fluid between rotating parallel disks: analysis for the oldroyd-B fluid. J Fluid Mech 255:473–502
Öztekin A, Brown RA, McKinley GH (1994) Quantitative prediction of the viscoelastic instability in cone-and-plate flow of a Boger fluid using a multi-mode Giesekus model. J Non-Newtonian Fluid Mech 54:351–377
Quinzani LM, McKinley GH, Brown RA, Armstrong RC (1990) Modeling the theology of polyisobutylene solutions. J Rheol 34:705–748
Rangel-Nafaile C, Metzner AB, Wissbrun KF (1984) Analysis of stress-induced phase separations in polymer solutions. Macromolecules 17:1187–1195
Shaqfeh ESG (1996) Purely elastic instabilities in viscomerric flows. Ann Rev Fluid Mech 28:129–185
Solomon MJ, Mullet SJ (1996a) Study of mixed solvent quality in a polystyrenedioctyl phthalate-polystyrene system. J Poly Sci: B 34:181–192
Solomon MJ, Muller SJ (1996b) Flow past a sphere in polystyrene-based Boger fluids: the effect on the drag coefficient of finite extensibility, solvent quality and polymer molecular weight. J Non-Newtonian Fluid Mech 62:81–94
Tirtaatmadja V, Uhlherr PHT, Sridhar T (1990) Creeping motion of spheres in fluid M1. J Non-Newtonian Fluid Mech 35:327–337
Walters K, Tanner RI (1992) The motion of a sphere through an elastic fluid. In: Chhabra RP, DeKee D (eds) Transport processes in bubbles, drops, and particles. Hemisphere, New York, pp 73–86
Yanase H, Moldenaers P, Mewis J, Abetz V, van Egmond J, Fuller GG (1991) Structure and dynamics of a polymer solution subject to flow-induced phase separation. Rheol Acta 30:89–97
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
MacDonald, M.J., Muller, S.J. Shear rheology of polymer solutions near the critical condition for elastic instability. Rheola Acta 36, 97–109 (1997). https://doi.org/10.1007/BF00366816
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00366816