论文标题
球形纳米颗粒分散体的剪切稀疏和增厚
Shear thinning and thickening in spherical nanoparticle dispersions
论文作者
论文摘要
我们介绍了简单流体中刚性球形纳米颗粒流动的分子动力学研究。我们评估色散的粘度是剪切速率和纳米颗粒体积分数的函数。随着剪切速率的增加，我们观察到剪切稀薄的行为，剪切力克服了布朗力，从而导致纳米颗粒之间更频繁，更剧烈的碰撞。这反过来导致更多的耗散。我们表明，为了处于剪切变薄状态，纳米颗粒必须将自己命令为纵向层，以最大程度地减少碰撞。随着纳米颗粒体积分数的增加，形成有序层的空间较小，因此，随着剪切速率增加纳米颗粒的碰撞更多，这又导致剪切增厚。最有趣的是，我们表明，在中间体积分数下，系统表现出亚稳定性，沿着同一轨迹具有一系列有序和无序状态。我们的结果表明，对于简单流体中的纳米颗粒，不存在水力聚类现象，而是订购级别的转变是从剪切变薄到剪切增厚的过渡的主要机制。
We present a molecular dynamics study of the flow of rigid spherical nanoparticles in a simple fluid. We evaluate the viscosity of the dispersion as a function of shear rate and nanoparticle volume fraction. We observe shear thinning behavior at low volume fractions, as the shear rate increases, the shear forces overcome the brownian forces, resulting in more frequent and more violent collisions between the nanoparticles. This in turn results in more dissipation. We show that in order to be in the shear thinning regime the nanoparticle have to order themselves into layers longitudinal to the flow to minimize the collisions. As the nanoparticle volume fraction increases there is less room to form the ordered layers, consequently as the shear rate increases the nanoparticles collide more which results in turn in shear thickening. Most interestingly, we show that at intermediate volume fractions the system exhibits metastability, with successions of ordered and disordered states along the same trajectory. Our results suggest that for nanoparticles in a simple fluid the hydro-clustering phenomenon is not present, instead the order-disorder transition is the leading mechanism for the transition from shear thinning to shear thickening.
