Fluidization dynamics of a simple yield stress fluid: a long way from transient shear banding to steady state

Details Fluidization dynamics of a simple yield stress fluid: a long way from transient shear banding to steady state Fluidization dynamics of a simple yield stress fluid: a long way from transient shear banding to steady state

2011-10-09

arxiv.org/abs/1110.1786v1

Physics

Condensed Matter

Soft Condensed Matter

15 pages, 16 figures, submitted to Soft Matter

Scientific paper

The shear-induced fluidization of a carbopol microgel is investigated during long start-up experiments using combined rheology and velocimetry in Couette cells of varying gap widths and boundary conditions. As already described in [Divoux et al., Phys. Rev. Lett., 2010, 104, 208301], we show that the fluidization process of this simple yield stress fluid involves a transient shear-banding regime whose duration tau_f decreases as a power law of the applied shear rate gp. We complete our previous findings by an investigation of the influence of the shearing geometry through the gap width e and the boundary conditions. While slip conditions at the walls seem to have a negligible influence on the fluidization time tau_f, different fluidization processes are observed depending on gp and e: the shear band remains almost stationary for several hours at low shear rates or small gap widths before strong fluctuations lead to a homogeneous flow whereas at larger values of gp or e, the transient shear band is seen to invade the whole gap in a much smoother way. Finally, by comparing local and global rheological measurements, we emphasize that the steady state reached by our samples is fully compatible with that expected for a simple yield stress fluid described by a Herschel-Bulkley behaviour.

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