Abstract
Semi-dilute (\(c^\ast ce) solutions of PEO yield uniformly thinning, cylindrical filaments in capillary breakup extensional rheometry (CaBER) experiments. Up to c ≈ ce thinning can be characterized by a single elongational relaxation time λE. Comparison with the longest shear relaxation time, λS reveals that λE/λS decreases with increasing concentration or molecular weight according to (c[η]) − 4/3. This is attributed to the large deformation the solutions experience during filament thinning. A factorable integral model including a single relaxation time and a Soskey or Wagner damping function accounting for the large deformation in CaBER experiments is used to calculate λE/λS and provides good agreement with experimental results. Irrespective of concentration or molecular weight a beads-on-a-string structure occurs prior to filament breakup at a diameter ratio D/D0 ≈ 0.01. This instability is supposed to be closely related to a flow-induced phase separation.
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