Das Mohan, Chambon Lucille, Varga Zsigmond, Vamvakaki Maria, Swan James W, Petekidis George
IESL - FORTH and Department of Material Science and Technology, University of Crete, GR - 71110, Heraklion, Greece.
Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Soft Matter. 2021 Feb 15;17(5):1232-1245. doi: 10.1039/d0sm01576h.
A combination of rheology, optical microscopy and computer simulations was used to investigate the microstructural changes of a semi-dilute suspension of attractive rigid rods in an imposed shear flow. The aim is to understand the relation of the microstructure with the viscoelastic response, and the yielding and flow behaviour in different shear regimes of gels built from rodlike colloids. A semi-dilute suspension of micron sized, rodlike silica particles suspended in 11 M CsCl salt solution was used as a model system for attractive rods' gel. Upon application of steady shear the gel microstructure rearranges in different states and exhibits flow instabilities depending on shear rate, attraction strength, volume fraction and geometrical confinement. At low rod volume fractions, the suspension forms large, vorticity aligned, particle rich flocs that roll in the flow-vorticity plane, an effect that is due to an interplay between hydrodynamic interactions and geometrical confinement as suggested by computer simulations. Experimental data allow the creation of a state diagram, as a function of volume fraction and shear rates, identifying regimes of stable (or unstable) floc formation and of homogeneous gel or broken clusters. The transition is related to dimensionless Mason number, defined as the ratio of shear forces to interparticle attractive force.
采用流变学、光学显微镜和计算机模拟相结合的方法，研究了在施加剪切流作用下，具有吸引力的刚性棒状颗粒半稀悬浮液的微观结构变化。目的是了解微观结构与粘弹性响应之间的关系，以及由棒状胶体构成的凝胶在不同剪切状态下的屈服和流动行为。将微米级的棒状二氧化硅颗粒悬浮在11M CsCl盐溶液中形成的半稀悬浮液用作具有吸引力的棒状颗粒凝胶的模型体系。施加稳定剪切时，凝胶微观结构会根据剪切速率、吸引力强度、体积分数和几何限制等因素，重排为不同状态并表现出流动不稳定性。在低棒状颗粒体积分数下，悬浮液形成大的、与涡度对齐的、富含颗粒的絮凝物，这些絮凝物在流动-涡度平面内滚动，计算机模拟表明，这是由于流体动力学相互作用和几何限制之间的相互作用所致。实验数据允许绘制出作为体积分数和剪切速率函数的状态图，确定稳定（或不稳定）絮凝物形成以及均匀凝胶或破碎团簇的区域。这种转变与无量纲梅森数有关，无量纲梅森数定义为剪切力与颗粒间吸引力的比值。
