Piednoir Agnès, Steinberger Audrey, Cottin-Bizonne Cécile, Barentin Catherine
Université de Lyon, Université Claude Bernard Lyon 1, CNRS, Institut Lumière Matière, F-69622 Villeurbanne, France.
Université de Lyon, ENS de Lyon, Université Claude Bernard, CNRS, Laboratoire de Physique, 69364 Lyon, France.
J Phys Chem B. 2020 Apr 2;124(13):2685-2690. doi: 10.1021/acs.jpcb.0c01760. Epub 2020 Mar 19.
A significant viscosity variation with the shear rate has been observed for several ionic liquids in rheometry experiments above a critical shear rate. Depending on the liquid and the rheological conditions, both viscosity increase and decrease have been reported. So far, these variations have been interpreted as a signature of a non-Newtonian behavior. However, the measured critical shear rates are orders of magnitude below the ones predicted by numerical simulations. In this work, we perform new rheometry experiments with both ionic liquids and Newtonian liquids to elucidate this discrepancy. For these two types of liquids, both a viscosity decrease and increase have been measured depending on the geometry of the rheometer and the zero-shear viscosity of the liquid. We interpret the viscosity decrease as resulting from viscous heating, since the viscosity of the investigated liquids is also highly temperature-dependent, and the viscosity increase as resulting from the development of instabilities at high shear rates.
在高于临界剪切速率的流变学实验中，已观察到几种离子液体的粘度随剪切速率有显著变化。根据液体和流变条件的不同，既有粘度增加的报道，也有粘度降低的报道。到目前为止，这些变化被解释为非牛顿行为的特征。然而，测得的临界剪切速率比数值模拟预测的低几个数量级。在这项工作中，我们对离子液体和牛顿液体都进行了新的流变学实验，以阐明这种差异。对于这两种类型的液体，根据流变仪的几何形状和液体的零剪切粘度，既测量到了粘度降低，也测量到了粘度增加。我们将粘度降低解释为粘性加热的结果，因为所研究液体的粘度也高度依赖于温度，而粘度增加则是由于高剪切速率下不稳定性的发展所致。
