Role of Attractions in Modifying the Confined Flow of Colloids

CBET 1438204当颗粒（如刚性球体）的浓缩悬浮液流过狭窄通道时，颗粒有远离通道壁并向通道中心迁移的趋势。 这种现象被称为剪切诱导迁移。 它影响流过通道的颗粒的排列以及颗粒由于流动而形成的结构。 窄通道中的浓缩悬浮液流出现在几种新的技术应用中，包括半固体液流电池和用于3D打印的浓缩纳米颗粒油墨。 这个项目将研究粒子之间吸引力的影响。 初步数据表明，颗粒间的吸引力可以抑制剪切引起的迁移。 将进行一系列的实验，以确定颗粒之间的吸引力是否会产生减少迁移的颗粒的瞬时簇或聚集体，这可以提供一种方法，以更好地定制颗粒材料的特定应用的兴趣。实验将量化颗粒间的吸引力对剪切诱导迁移的影响，并将相关的剪切诱导迁移的程度与悬浮液的微观结构。 通过向硬球悬浮液中添加少量聚合物以在颗粒之间产生耗尽力来实现颗粒间吸引力。 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和所得悬浮液结构的影响。 将确定只涉及硬球相互作用的剪切引起的迁移的现象学模型的偏差。 悬浮液的微观结构将与剪切引起的迁移的程度，通过使用3-D共聚焦成像和跟踪测量颗粒分布函数，簇的大小，和流动过程中的速度波动。 还将通过化学修饰壁以改变其表面能来研究通道壁边界条件的影响。

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.