Robyn L. Moorcroft, Suzanne M. Fielding
Within a highly generalised theoretical framework for the flow properties of
complex fluids, we study the onset of shear banding in the three most common
time-dependent experimental protocols: step stress, step strain and shear
startup. By means of a linear stability analysis we derive a fluid-universal
criterion for the onset of banding, separately for each protocol, that depends
only on the shape of the experimentally measured time-dependent rheological
response function, independent of the constitutive law and internal state
variables of the particular fluid in question. Our predictions thus have the
same status, in these time-dependent flows, as the widely known criterion for
banding in steady state (of negatively sloping shear stress vs. shear rate). We
support them with simulations of the rolie-poly model of polymeric fluids, the
soft glassy rheology model, and a fluidity model.
View original:
http://arxiv.org/abs/1201.6259
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