Rossi Emanuele, Ruiz-Lopez Jose A, Vázquez-Quesada A, Ellero M
Basque Center for Applied Mathematics (BCAM), Alameda de Mazarredo 14, 48009 Bilbao, Spain.
Department of Physics and Mathematics, Universidad de Alcalá, 28801 - Alcalá de Henares, Madrid, Spain.
Soft Matter. 2021 Jun 23;17(24):6006-6019. doi: 10.1039/d0sm01173h.
This study presents an analysis of the dynamics of single and multiple chains of spherical super-paramagnetic beads suspended in a Newtonian fluid under the combined effect of an external rotating magnetic field and a shear flow. Viscosity results depend on two main non-dimensional numbers: the ratio between the shear rate and the magnetic rotation frequency and the ratio between the hydrodynamic and magnetostatic interactions (the Mason number). When the shear rate is smaller than the magnetic field frequency, the chain rotation accelerates the surrounding fluid, reducing the value of the measured suspension viscosity even below that of the solvent. In this regime, shear-thickening is observed. For values of the shear rates comparable to the rotation magnetic frequency, the viscosity reaches a maximum and non-linear coupling effects come up. If the shear rate is increased to values above the rotation frequency, the viscosity decreases and a mild shear-thinning is observed. In terms of the Mason number, the suspension viscosity reduces in line with the literature results reported for fixed magnetic fields, whereas the shear-rate/magnetic-frequency ratio parameters induce a shift of the viscosity curve towards larger values. Results at larger concentrations and multiple chains amplify the observed effects.
本研究分析了在外部旋转磁场和剪切流的共同作用下，悬浮于牛顿流体中的单链和多链球形超顺磁珠的动力学。粘度结果取决于两个主要的无量纲数：剪切速率与磁旋转频率之比以及流体动力相互作用与静磁相互作用之比（梅森数）。当剪切速率小于磁场频率时，链的旋转会加速周围流体，使测得的悬浮液粘度值甚至低于溶剂的粘度值。在这种情况下，会观察到剪切增稠现象。当剪切速率的值与旋转磁频率相当时，粘度达到最大值，并且会出现非线性耦合效应。如果将剪切速率增加到高于旋转频率的值，则粘度会降低，并观察到轻微的剪切变稀现象。就梅森数而言，悬浮液粘度的降低与固定磁场下报道的文献结果一致，而剪切速率/磁频率比参数会使粘度曲线向更大的值偏移。更高浓度和多链的结果放大了所观察到的效应。
