Role of Attractions in Modifying the Confined Flow of Colloids

CBET 1438204当像刚性球这样的颗粒的集中悬浮液流过狭窄的通道时，颗粒有离开壁面并向通道中心迁移的趋势。这种现象被称为剪切诱导迁移。它影响流经通道的颗粒的排列以及颗粒作为流动的结果形成的结构。浓缩悬浮液在狭窄通道中的流动出现在几种新的技术应用中，包括半固态流动电池和用于3D打印的浓缩纳米颗粒墨水。这个项目将研究粒子之间引力的影响。初步数据表明，粒间引力可以抑制剪切诱导的迁移。将进行一系列实验，以确定颗粒之间的引力是否会产生减少迁移的瞬时颗粒团簇或聚集，从而为特定的兴趣应用提供一种更好地定制颗粒材料的方法。实验将量化颗粒间吸引对剪切诱导迁移的影响，并将悬浮体微观结构与剪切诱导迁移的程度相关联。颗粒间的吸引将通过在硬球悬浮液中加入少量聚合物来实现，以在颗粒之间产生衰减力。将测量吸引范围和强度、胶体体积分数和流速对剪切诱导迁移的影响以及由此产生的悬浮液的结构。只涉及硬球相互作用的剪切诱导迁移的唯象模型的偏差将被确定。通过使用三维共聚焦成像和跟踪来测量颗粒分布函数、团簇大小和流动过程中的速度波动，悬浮微结构将与剪切诱导的迁移程度相关联。还将通过对通道壁进行化学修饰以改变其表面能量来研究边界条件对通道壁的影响。

CBET 1438204When a concentrated suspension of particles such as rigid spheres flows through a narrow channel, there is a tendency for the particles to migrate away from the walls and toward the center of the channel. This phenomenon is called shear-induced migration. It affects the arrangement of the particles flowing through the channel and the structures that the particles form as a result of the flow. Flows of concentrated suspensions in narrow channels occur in several novel technological applications, including semi-solid flow batteries and concentrated nanoparticle inks for 3D printing. This project will investigate the effects of attractive forces between the particles. Preliminary data show that interparticle attractions can suppress shear-induced migration. A series of experiments will be conducted to determine whether attractive forces between particles give rise to transient clusters or aggregates of particles that reduce migration, which could provide a way to better tailor particulate materials for specific applications of interest.Experiments will quantify effects of interparticle attraction on shear-induced migration and will correlate suspension microstructure with the extent of shear-induced migration. The interparticle attraction will be achieved by adding small amounts of polymer to suspensions of hard spheres to create a depletion force between particles. The effects of attraction range and strength, colloid volume fraction, and flow rate on shear-induced migration and the structure of the resulting suspension will be measured. Deviations from phenomenological models for shear-induced migration that involve only hard sphere interactions will be determined. Suspension microstructure will be correlated with the extent of shear-induced migration by using 3-D confocal imaging and tracking to measure particle distribution functions, cluster sizes, and velocity fluctuations during flow. Effects of boundary conditions at channel walls will also be investigated by chemically modifying the walls to change their surface energy.