The design of flow processes to build a macroscopic bulk material from rod-shaped colloidal particles has drawn considerable attention from researchers and engineers. Here, we systematically explore and show that the characteristic strain rate of the flow universally determines the orientational ordering of colloidal rods. We employed the fluctuating lattice Boltzmann method by simulating hydrodynamically interacting Brownian rods in a Newtonian liquid moving under various flow types. By modeling a rigid rod as a chain of nonoverlapping solid spheres with constraint forces and torque, we elucidate rigid rod dynamics with an aspect ratio ($L/d$) either 4.1 or 8.1 under various rotational Péclet number ($P{e}_r$) conditions. The dynamics of colloidal rods in dilute ($n{L}^3=0.05$) and semidilute suspensions ($n{L}^3=1.1$) were simulated for a wide range of $P{e}_r$ ($0.01<P{e}_r<1000$) under shear flows including Couette and Poiseuille flows in a planar channel geometry, and an extensional and mixed-kinematics flow in a periodic four-roll mill geometry, where $n$ is the number density, and $d$ and $L$ are the diameter and length of the rod, respectively. By evaluating the degree of orientational alignment of rods along the flows, we observed that there is no significant difference between flow types, and the flow-induced ordering of rods depends on the variation of $P{e}_r$ up to moderate $P{e}_r$ ($P{e}_r<100$). At a high $P{e}_r$ ($P{e}_r>100$), the degree of orientational ordering is prone to diversify depending on the flow type. The spatial inhomogeneity of the strain-rate distribution leads to a substantial decrease in the orientational alignment at high $P{e}_r$.

中文翻译：

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平面剪切流和拉伸流中胶体棒的普遍流动诱导定向排序：稀释和半稀释浓度

从棒状胶体颗粒构建宏观散装材料的流动过程设计引起了研究人员和工程师的相当大的关注。在这里，我们系统地探索并表明流动的特征应变率普遍决定了胶体棒的定向排序。我们通过模拟在各种流动类型下移动的牛顿液体中流体动力学相互作用的布朗棒，采用波动格子玻尔兹曼方法。通过将刚性杆建模为一连串具有约束力和扭矩的非重叠实心球体，我们阐明了具有长宽比的刚性杆动力学（$\mathrm{大号}/d$) 在各种旋转 Péclet 数下为 4.1 或 8.1 ($P{\mathrm{电子}}_r$） 状况。胶体棒在稀溶液中的动力学（$n{\mathrm{大号}}^{\mathrm{3个}}=0.05$) 和半稀释悬浮液 ($n{\mathrm{大号}}^{\mathrm{3个}}=1.1$）被模拟了广泛的$P{\mathrm{电子}}_r$($0.01<P{\mathrm{电子}}_r<1000$) 在剪切流下，包括平面通道几何中的 Couette 和 Poiseuille 流，以及周期性四辊磨机几何中的拉伸和混合运动学流，其中$n$是数密度，和$d$和$\mathrm{大号}$分别是杆的直径和长度。通过评估棒沿流的定向排列程度，我们观察到流类型之间没有显着差异，并且流诱导的棒排序取决于$P{\mathrm{电子}}_r$至中度$P{\mathrm{电子}}_r$($P{\mathrm{电子}}_r<100$). 在高处$P{\mathrm{电子}}_r$($P{\mathrm{电子}}_r>100$），定向排序的程度很容易根据流类型而多样化。应变率分布的空间不均匀性导致高处的取向对准显着降低$P{\mathrm{电子}}_r$.