Department of Chemical Engineering, KU Leuven, 3001 Leuven, Belgium.
Institute of Electronic Structure and Laser, FORTH, P.O. Box 1527, 70013 Heraklion, Crete Greece.
Phys Rev Lett. 2019 Nov 22;123(21):218003. doi: 10.1103/PhysRevLett.123.218003.
Stress relaxation upon cessation of shear flow is known to be described by single-mode or multimode monotonic exponential decays. This is considered to be ubiquitous in nature. However, we found that, in some cases, the relaxation becomes anomalous in that an increase in the relaxing stress is observed. Those observations were made for physicochemically very different systems, having in common, however, the presence of self-associating units generating structures at large length scales. The nonmonotonic stress relaxation can be described phenomenologically by a generic model based on a redistribution of energy after the flow has stopped. When broken bonds are reestablished after flow cessation, the released energy is partly used to locally increase the elastic energy by the formation of deformed domains. If shear has induced order such that these elastic domains are partly aligned, the reestablishing of bonds gives rise to an increase of the overall stress.
停止剪切流动后，应力松弛通常可通过单模态或多模态单调指数衰减来描述。这在自然界中被认为是普遍存在的。然而，我们发现，在某些情况下，松弛会变得异常，即观察到松弛应力增加。这些观察结果是在物理化学性质非常不同的系统中得到的，但它们有一个共同的特点，即存在自组装单元，在大的长度尺度上产生结构。非单调的应力松弛可以通过一个通用模型来进行唯象描述，该模型基于流动停止后能量的再分配。当流动停止后重新形成断裂键时，释放的能量部分用于通过形成变形域来局部增加弹性能量。如果剪切作用诱导了某种有序，使得这些弹性域部分对齐，那么重新形成的键会导致整体应力增加。
