Oscillatory shear flow instability

Monodisperse melts appear to exhibit a plateau region in the stress vs shear rate flow curve [51,62,65]. The capillary flow behavior actually closely resembles the oscillatory shear behavior in the sense that the flow curve essentially overlaps on the absolute value of complex modulus G vs the oscillation frequency (0 [62]. Thus.it appears that the transition-like capillary flow behavior of highly entangled monodisperse melts reflects constitutive bulk properties of the melts and is not interfacial in origin. It remains to be explored whether this plateau indeed manifests a real constitutive instability, i.e., whether it is double-valued. 

M.G. Clark, F.C. Saunders, LA. Shanks and F.M. Leslie, A Study of Flow Alignment Instability During Rectilinear Oscillatory Shear of Nematics, Mol Cryst Liq. Cryst, 70, 195-222 (1981). 

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