Edens Lance E, Alvarado Enrique G, Singh Abhinendra, Morris Jeffrey F, Schenter Gregory K, Chun Jaehun, Clark Aurora E
Department of Chemistry, Washington State University, USA.
Soft Matter. 2021 Aug 28;17(32):7476-7486. doi: 10.1039/d1sm00184a. Epub 2021 Jul 22.
The geometric organization and force networks of 3D dense suspensions that exhibit both shear thinning and thickening have been examined as a function of varying strength of interparticle attractive interactions using lubrication flow discrete element simulations. Significant rearrangement of the geometric topology does not occur at either the local or global scale as these systems transition across the shear thinning and shear thickening regimes. In contrast, massive rearrangements in the balance of attractive, lubrication, and contact forces are observed with interesting behavior of network growth and competition. In agreement with prior work, in shear thinning regions the attractive force is dominant, however as the shear thickening region is approached there is growth of lubrication forces. Lubrication forces oppose the attraction forces, but as viscosity continues to increase under increasing shear stress, the lubrication forces are dominated by contact forces that also resist attraction. Contact forces are the dominant interactions during shear thickening and are an order of magnitude higher than their values in the shear-thinning regime. At high attractive interaction strength, contact networks can form even under shear thinning conditions, however high shear stress is still required before contact networks become the driving mechanism of shear thickening. Analysis of the contact force network during shear thickening generally indicates a uniformly spreading network that rapidly forms across empty domains; however the growth patterns exhibit structure that is significantly dependent upon the strength of interparticle interactions, indicating subtle variations in the mechanism of shear thickening.
利用润滑流离散元模拟，研究了呈现剪切变稀和剪切增稠现象的三维致密悬浮液的几何结构和力网络，该研究将其作为颗粒间吸引相互作用强度变化的函数。当这些系统在剪切变稀和剪切增稠区域之间转变时，在局部或全局尺度上均未发生几何拓扑结构的显著重排。相比之下，观察到吸引力、润滑力和接触力平衡发生了大规模重排，同时伴随着网络生长和竞争的有趣行为。与先前的研究一致，在剪切变稀区域，吸引力占主导地位，然而随着接近剪切增稠区域，润滑力会增大。润滑力与吸引力相反，但随着剪切应力增加粘度持续上升时，润滑力由同样抵抗吸引力的接触力主导。在剪切增稠过程中，接触力是主要相互作用，其值比在剪切变稀区域高一个数量级。在高吸引相互作用强度下，即使在剪切变稀条件下也能形成接触网络，然而在接触网络成为剪切增稠的驱动机制之前，仍需要高剪切应力。对剪切增稠过程中接触力网络的分析通常表明，会形成一个均匀扩展的网络，该网络会在空区域迅速形成；然而，生长模式呈现出显著依赖于颗粒间相互作用强度的结构，这表明剪切增稠机制存在细微变化。
