SHEAR AND ELONGATIONAL FLOW PROPERTIES OF FLUID S1 FROM ROTATIONAL, CAPILLARY, AND OPPOSED JET RHEOMETRY

Non-linear shear and elongational flow properties of the ternary fluid S1 have been compared to those of a binary solution with similar line ar viscoelastic properties. In contrast to the binary solution, fluid S1 exhibits a flow instability. The onset of this instability in rotat ional flow is characterized by a critical Deborah number De(c) = 13.5. Secondary flow causes an irreversible decrease of zero-shear viscosit y. A flow-induced degradation of the dissolved polymer has been proved by different analytical methods. However, this effect is not sufficie nt to account for the observed reduction of eta0, and it is speculated that the irregular flow additionally gives rise to a phase separation or demixing of the originally homogeneous solution. Up to now there i s no direct experimental evidence for this hypothesis. Elongational fl ow properties have been characterized by means of an opposing jet appa ratus. Apparent elongational viscosity of fluid S1 increases strongly with increasing apparent elongation rate epsilon and total strain epsi lon. A strain-independent equilibrium value is not reached. In the cas e of the binary solution eta(E) is independent of e and increases only slightly with increasing epsilon. Strong fluctuations of the force si gnal are observed in the case of fluid S1 when a critical flow rate is exceeded, indicating secondary flow phenomena.