Shear thickening in stable dense colloidal suspensions is a reversible phenomenon and no hysteresis is observed in the flow curve measurements. However, a reduction in the stability of colloids promotes particle aggregation and introduces a time dependent rheological response. In this work, by using a model colloidal system of hard spherical silica particles (average diameter of 415 nm) with varying particle volume fractions 0.2 ≤ ϕ ≤ 0.56, we study the effect of particle stability on the hysteresis of the shear thickening behavior of these suspensions. The particle stability is manipulated by adding a simple monovalent salt (sodium chloride) in the silica suspension with varying concentrations α ∈ [0,0.5] M. For repulsive and weakly attractive suspensions, the flow behavior is history independent and the shear thickening behavior does not exhibit hysteresis. However, significant hysteresis is observed in rheological measurements for strongly attractive suspensions, with shear history playing a critical role due to the dynamic nature of particle clusters, resulting in time dependent hysteresis behavior. By performing numerical simulations, we find that this hysteresis behavior arises due to the competition among shear, electrostatic repulsive, van der Waals attractive, and frictional contact forces. The critical shear stress (i.e., the onset of shear thickening) decreases with increasing salt concentrations, which can be captured by a scaling relationship based on the force balance between particle–particle contact force and electrostatic repulsive force. Our combined experimental and simulation results imply the formation of particle contacts in our sheared suspensions.

中文翻译：

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硬球的密集排斥和有吸引力的悬浮液中的剪切增稠行为

稳定致密胶体悬浮液中的剪切增稠是一种可逆现象，在流动曲线测量中没有观察到滞后现象。然而，胶体稳定性的降低会促进颗粒聚集并引入时间相关的流变响应。在这项工作中，通过使用具有不同颗粒体积分数 0.2 ≤ φ ≤ 0.56的硬球形二氧化硅颗粒（平均直径为 415 nm）的模型胶体系统，我们研究了颗粒稳定性对这些颗粒剪切增稠行为滞后的影响暂停。通过在二氧化硅悬浮液中添加不同浓度α的简单单价盐（氯化钠）来控制颗粒稳定性∈ [0,0.5] M。对于排斥性和弱吸引力的悬浮液，流动行为与历史无关，剪切增稠行为不表现出滞后现象。然而，在强吸引力悬浮液的流变测量中观察到显着滞后，由于粒子簇的动态特性，剪切历史起着关键作用，导致时间依赖性滞后行为。通过进行数值模拟，我们发现这种滞后行为是由于剪切力、静电排斥力、范德华引力和摩擦接触力之间的竞争而产生的。临界剪应力（即，剪切增稠的开始）随着盐浓度的增加而减少，这可以通过基于粒子 - 粒子接触力和静电排斥力之间的力平衡的比例关系来捕获。我们的综合实验和模拟结果表明在我们的剪切悬浮液中形成了颗粒接触。