Université de Lyon, Laboratoire de Physique, Ecole Normale Supérieure de Lyon, CNRS UMR 5672, 46 Allée d'Italie, 69364 Lyon cedex 07, France.
Phys Rev Lett. 2010 May 21;104(20):208301. doi: 10.1103/PhysRevLett.104.208301. Epub 2010 May 18.
We report a large set of experimental data which demonstrates that a simple yield stress fluid, i.e., which does not present aging or thixotropy, exhibits transient shear banding before reaching a steady state characterized by a homogeneous, linear velocity profile. The duration of the transient regime decreases as a power law with the applied shear rate γ. This power-law behavior, observed here in carbopol dispersions, does not depend on the gap width and on the boundary conditions for a given sample preparation. For γ≲0.1 s(-1), heterogeneous flows could be observed for as long as 10(5) s. These local dynamics account for the ultraslow stress relaxation observed at low shear rates.
我们报告了一组大量的实验数据，这些数据表明，一种简单的屈服应力流体（即没有老化或触变现象）在达到稳态之前会表现出瞬态剪切带，其特征是均匀的线性速度分布。瞬变阶段的持续时间随施加的剪切率γ呈幂律减小。这种幂律行为在卡波普分散体中观察到，不依赖于给定样品制备的间隙宽度和边界条件。对于γ≲0.1 s(-1)，可以观察到长达 10(5) s 的非均匀流动。这些局部动力学解释了在低剪切速率下观察到的超慢速应力松弛现象。
