ESPCI Paris, PSL Research University, Sciences et Ingénierie de la Matière Molle, CNRS UMR 7615, 10 rue Vauquelin, F-75231 Paris Cedex 05, France.
Laboratoire de Physique Statistique, Ecole Normale Supérieure, UMR CNRS 8550, PSL Research University, 24 rue Lhomond, 75005 Paris Cedex 05, France.
Soft Matter. 2018 Feb 14;14(6):879-893. doi: 10.1039/c7sm01963g. Epub 2017 Dec 7.
We study the flow of suspensions of non-Brownian particles dispersed into a Newtonian solvent. Combining capillary rheometry and conventional rheometry, we evidence a succession of two shear thinning regimes separated by a shear thickening one. Through X-ray radiography measurements, we show that during each of those regimes, the flow remains homogeneous and does not involve particle migration. Using a quartz-tuning fork based atomic force microscope, we measure the repulsive force profile and the microscopic friction coefficient μ between two particles immersed into the solvent, as a function of normal load. Coupling measurements from those three techniques, we propose that (1) the first shear-thinning regime at low shear rates occurs for a lubricated rheology and can be interpreted as a decrease of the effective volume fraction under increasing particle pressures, due to short-ranged repulsive forces and (2) the second shear thinning regime after the shear-thickening transition occurs for a frictional rheology and can be interpreted as stemming from a decrease of the microscopic friction coefficient at large normal load.
我们研究了非布朗粒子悬浮液在牛顿溶剂中的流动。通过结合毛细管流变仪和传统流变仪，我们证明了存在连续的两个剪切变稀区域，其间夹着一个剪切增稠区域。通过 X 射线射线照相测量，我们表明在这些区域中的每一个区域，流动仍然是均匀的，并且不涉及颗粒迁移。使用基于石英音叉的原子力显微镜，我们测量了浸入溶剂中的两个粒子之间的排斥力曲线和微观摩擦系数 μ，作为法向载荷的函数。结合这三种技术的测量结果，我们提出（1）在低剪切速率下的第一个剪切变稀区域发生在润滑流变学中，可以解释为由于短程排斥力导致有效体积分数在颗粒压力增加时降低，（2）在剪切增稠转变后的第二个剪切变稀区域发生在摩擦流变学中，可以解释为由于在大法向载荷下微观摩擦系数降低所致。
