Transient Shear Banding in a Simple Yield Stress Fluid

摘要: We report a large set of experimental data which demonstrates that simple yield stress fluid, i.e., does not present aging or thixotropy, exhibits transient shear banding before reaching steady state characterized by homogeneous, linear velocity profile. The duration the regime decreases as power law with applied rate $\stackrel{\ifmmode \dot{}\else \textperiodcentered \fi{}}{\ensuremath{\gamma}}$. This power-law behavior, observed here in carbopol dispersions, depend on gap width and boundary conditions for given sample preparation. For \fi{}}{\ensuremath{\gamma}}\ensuremath{\lesssim}0.1\text{ }\text{ }{\mathrm{s}}^{\ensuremath{-}1}$, heterogeneous flows could be long ${10}^{5}\text{ }\mathrm{s}$. These local dynamics account ultraslow relaxation at low rates.