Fall A, Bertrand F, Hautemayou D, Mezière C, Moucheront P, Lemaître A, Ovarlez G
Laboratoire Navier (UMR CNRS 8205), Université Paris Est, 77420 Champs-sur-Marne, France.
Phys Rev Lett. 2015 Mar 6;114(9):098301. doi: 10.1103/PhysRevLett.114.098301. Epub 2015 Mar 3.
We study the emergence of discontinuous shear thickening (DST) in cornstarch by combining macroscopic rheometry with local magnetic resonance imaging measurements. We bring evidence that macroscopic DST is observed only when the flow separates into a low-density flowing and a high-density jammed region. In the shear-thickened steady state, the local rheology in the flowing region is not DST but, strikingly, is often shear thinning. Our data thus show that the stress jump measured during DST, in cornstarch, does not capture a secondary, high-viscosity branch of the local steady rheology but results from the existence of a shear jamming limit at volume fractions quite significantly below random close packing.
我们通过将宏观流变学与局部磁共振成像测量相结合，研究了玉米淀粉中不连续剪切增稠（DST）的出现。我们提供的证据表明，只有当流动分离为低密度流动区域和高密度堵塞区域时，才会观察到宏观DST。在剪切增稠稳态下，流动区域的局部流变学不是DST，而是令人惊讶地经常出现剪切变稀。因此，我们的数据表明，在玉米淀粉中DST期间测量到的应力跳跃，并未捕捉到局部稳态流变学的二级高粘度分支，而是源于在体积分数远低于随机密堆积时存在的剪切堵塞极限。
