Collaborative Research: Micromechanics of Meniscus-bound Particle Clusters

表面张力现象在各种物理过程中都很重要，包括不相容流体的混合、喷雾和气雾剂的形成以及塑料发泡。这个合作项目涉及颗粒-液体混合物，通常被称为颗粒悬浮液。例如，矿物和陶瓷加工过程中遇到的泥浆、填充颗粒的熔融塑料和印刷油墨。在这种颗粒悬浮液中，由于表面张力和毛细管力的作用，第二个不相容的液体的加入会导致颗粒的“粘连”和聚集。一个熟悉的例子是沙堡，它的强度来自于微小的水滴，这些水滴通过毛细管力将沙粒结合在一起。该项目将对混合流中的颗粒间毛细管力进行基础研究。被毛细管力束缚的粒子团将被放置在定义明确的流动中，并使用自动化流动控制的新方法进行研究。这项工作的目的是了解颗粒团簇的流动动力学及其稳定性的极限，稳定性极限指的是团簇由于外加流动而破裂的条件。在过去的十年里，表面张力诱导的颗粒聚集已经被广泛地用于材料和材料加工应用，包括大孔陶瓷、3D打印、导电塑料和印刷电子电路。该项目的结果将有助于合理设计混合操作，利用毛细管力开发新材料。在含有颗粒和两种不相容液体的多相悬浮液中，毛细管力可以诱导颗粒聚集。这些团簇由两个或多个由弯月面液体结合的颗粒组成。在本项目中，将利用视频显微镜和自动流动控制技术来研究简单剪切或平面拉伸流场中颗粒团簇的动力学和破裂机理。一种名为斯托克斯陷阱的反馈控制微流控设备将被用来使用粘性力精确操纵粒子，创建定义明确的弯月面约束粒子簇，并使这些粒子簇受到精确控制的流动。这项工作旨在实现对定义明确的流动中粒子团簇的动力学和破裂的基本理解。该项目将从根本上揭示新的信息，包括粒子团破裂的标准，以及这些标准如何依赖于粒子团的组成、弯月面流体的粘度和粒子粗糙度。液体/液体/颗粒混合物的混合操作设计目前在本质上是经验性的。该项目将为利用毛细管力开发新材料的混合操作建立基于微观力学的设计规则。该项目将成为培养研究生和本科生的基础。两位首席研究员将在本科生和大学预科阶段开展大量外展活动，包括招募代表性不足的群体加入他们的研究小组，以及指导高中生。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Surface tension phenomena are important in a variety of physical processes including blending of immiscible fluids, formation of sprays and aerosols and foaming of plastics. This collaborative project concerns particle-liquid mixtures that are generally called particulate suspensions. Examples include slurries encountered in mineral and ceramics processing, particle-filled molten plastics, and printing inks. In such particulate suspensions, the addition of a second immiscible liquid induces particle "sticking" and aggregation due to surface tension and capillary forces. A familiar example is a sandcastle whose strength comes from small water droplets which bind the sand grains together by capillary forces. This project will conduct fundamental studies of interparticle capillary forces in mixing flows. Particle clusters bound by capillary forces will be placed in well-defined flows and studied using new methods in automated flow control. This work aims to understand the flow dynamics of particle clusters and the limits of their stability, which refers to the conditions under which clusters rupture due to the applied flow. Over the past decade, surface tension-induced particle clustering has been exploited for a wide range materials and materials-processing applications including macroporous ceramics, 3D printing, conductive plastics, and printing electronic circuits. The results of this project will enable rational design of mixing operations that exploit capillary forces to develop new materials.In multiphase suspensions containing particles and two immiscible liquids, capillary forces can induce particle clustering. The clusters comprise two or more particles bound by a meniscus liquid. In this project, the dynamics and rupture mechanics of particle clusters in simple shear or planar extensional flow fields will be studied using video microscopy and automated flow control. A feedback-controlled microfluidic device known as a Stokes trap will be used to precisely manipulate particles using viscous forces, to create well-defined meniscus-bound particle clusters, and to subject the clusters to precisely controlled flows. This work aims to achieve a fundamental understanding of the dynamics and rupture of particle clusters in well-defined flows. The project will reveal fundamentally new information, including the criteria for rupture of particle clusters, and how these criteria depend on the composition of the cluster, viscosity of the meniscus fluid, and particle roughness. Thedesign of mixing operations for liquid/liquid/particle mixtures is presently empirical in nature. This project will establish micromechanics-based design rules for such mixing operations that exploit capillary forces to develop new materials. The project will form the basis for training of graduate and undergraduate students. The two principal investigators will conduct numerous outreach activities at the undergraduate and pre-college level, including recruitment of underrepresented groups into their research groups, and mentorship of high-school students.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.