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The role of solvent molecular weight in shear thickening and shear jamming
Soft Matter ( IF 2.9 ) Pub Date : 2021-2-18 , DOI: 10.1039/d0sm01350a Mike van der Naald 1, 2, 3, 4, 5 , Liang Zhao 1, 2, 3, 4, 5 , Grayson L. Jackson 1, 2, 3, 4 , Heinrich M. Jaeger 1, 2, 3, 4, 5
Soft Matter ( IF 2.9 ) Pub Date : 2021-2-18 , DOI: 10.1039/d0sm01350a Mike van der Naald 1, 2, 3, 4, 5 , Liang Zhao 1, 2, 3, 4, 5 , Grayson L. Jackson 1, 2, 3, 4 , Heinrich M. Jaeger 1, 2, 3, 4, 5
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The application of stress can drive a dense suspension into a regime of highly non-Newtonian response, characterized by discontinuous shear thickening (DST) and potentially shear jamming (SJ), due to the formation of a frictionally stabilized contact network. Investigating how the molecular weight of the suspending solvent affects the frictional particle–particle interactions, we report on experiments with suspensions of fumed silica particles in polyethylene glycol (PEG). Focusing on the monomer-to-oligomer limit, with n = 1 to 8 ethylene oxide repeat units, we find that increasing n enhances shear thickening under steady-state shear and even elicits rapidly propagating shear jamming fronts, as assessed by high-speed ultrasound imaging of impact experiments. We associate this behavior with a weakening of the solvation layers surrounding the particles as n is increased, which thereby facilitates the formation of frictional contacts. We argue that for n larger than the monomer-to-oligomer limit the trend reverses and frictional interactions are diminished, as observed in prior experiments. This reversal occurs because the polymeric solvent transitions from being enthalpically bound to entropically bound to the particle surfaces, which strengthens solvation layers.
中文翻译：
溶剂分子量在剪切增稠和剪切堵塞中的作用
应力的施加可将致密的悬浮液驱动到高度非牛顿响应的状态，其特征在于由于形成了摩擦稳定的接触网络，从而导致不连续的剪切增稠（DST）和潜在的剪切堵塞（SJ）。为了研究悬浮溶剂的分子量如何影响颗粒间的摩擦相互作用，我们报告了气相二氧化硅在聚乙二醇（PEG）中的悬浮液的实验。着眼于单体到低聚物的限制，n = 1至8环氧乙烷重复单元，我们发现增加n通过冲击实验的高速超声成像评估，这种方法可以在稳态剪切下增强剪切增稠，甚至引起快速传播的剪切堵塞前沿。我们将这种行为与随着n的增加而削弱了围绕颗粒的溶剂化层的行为联系在一起，从而促进了摩擦接触的形成。我们认为，对于n大于单体与低聚物的极限值，趋势会发生逆转，并且如先前实验中观察到的那样，摩擦相互作用会减小。发生这种逆转是因为聚合物溶剂从焓结合转变为熵结合到颗粒表面，从而增强了溶剂化层。
更新日期：2021-02-18
中文翻译：
溶剂分子量在剪切增稠和剪切堵塞中的作用
应力的施加可将致密的悬浮液驱动到高度非牛顿响应的状态，其特征在于由于形成了摩擦稳定的接触网络，从而导致不连续的剪切增稠（DST）和潜在的剪切堵塞（SJ）。为了研究悬浮溶剂的分子量如何影响颗粒间的摩擦相互作用，我们报告了气相二氧化硅在聚乙二醇（PEG）中的悬浮液的实验。着眼于单体到低聚物的限制，n = 1至8环氧乙烷重复单元，我们发现增加n通过冲击实验的高速超声成像评估，这种方法可以在稳态剪切下增强剪切增稠，甚至引起快速传播的剪切堵塞前沿。我们将这种行为与随着n的增加而削弱了围绕颗粒的溶剂化层的行为联系在一起，从而促进了摩擦接触的形成。我们认为，对于n大于单体与低聚物的极限值，趋势会发生逆转，并且如先前实验中观察到的那样，摩擦相互作用会减小。发生这种逆转是因为聚合物溶剂从焓结合转变为熵结合到颗粒表面，从而增强了溶剂化层。
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