Interplay between orientation and lift forces on non-spherical particles in complex fluids

粘弹性悬浮液是含有颗粒的聚合流体。这些系统在我们的日常生活中无处不在，例如，在食品，消费品，涂料，粘合剂和糊状物（例如3D打印）中发现。这些系统在生物液体（如粘液、血液、细菌悬浮液）中也很常见。粘弹性悬浮液的一个有趣特征是，这种流体中的颗粒在压力驱动的流动中获得升力，这种压力驱动的流动将它们推向流体中的特定区域。这种现象在聚合物加工中很重要，因为它决定了材料的最终结构。它在微流体技术中也很重要，在微流体技术中，流动被用来根据颗粒大小和形状分离生物悬浮液。虽然人们对球形颗粒的升力进行了充分的研究，但人们对颗粒形状如何影响升力知之甚少，因为这种现象与颗粒方向高度耦合，而颗粒方向本身是流动的函数。该合同将进行实验、模拟和理论研究，以表征聚合物流体中非球形颗粒的运动，并量化不同流速、颗粒几何形状、流体性质和通道约束下升力和方向之间的耦合。在上述应用中，这些信息对于处理粘弹性悬浮液中的棒状和盘状颗粒很有价值，因为它为不同颗粒形状的迁移时间和最终位置提供了设计指导。本研究将特别进行微流体实验，在微流体实验中，人们将稀释的球体悬浮液（长形和扁形）流过一根管子。将使用不同的流体和通道尺寸，允许系统地改变流体特性和通道约束。粒子在不同通道位置的三维位置和方向分布将使用全息图可视化，允许人们获得粒子的长时间位置和迁移速率。直接的数值模拟和理论将补充研究，发展升力在这种几何形状以及其他几何形状的关系，这对流体表征很重要。两位研究人员将为普渡大学的女性工程项目制作复杂流体的演示，并为当地科学中心想象站的小学生制作类似的展览。这些展览将由在各自实验室工作的本科生和由研究人员建议的荣誉工程学会负责。最后，来自代表性不足社区的本科生将通过普渡大学的SURF项目被招募参加研究。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Viscoelastic suspensions are polymeric fluids containing particles. These systems are everywhere in our daily lives, for example, found in foods, consumer products, coatings, adhesives, and pastes (e.g., 3D printing). These systems are also common in biological fluids (e.g., mucous, blood, bacterial suspensions). One interesting feature of viscoelastic suspensions is that particles in such fluids acquire lift forces during pressure-driven flows that drive them toward specific regions in the fluid. This phenomenon is important in polymer processing because it determines the final structure of the materials. It is also important in microfluidic technologies where flow is used to separate biological suspensions by particle size and shape. While the lift forces are well-studied for spherical particles, little is known about how particle shape affects the lift because the phenomenon is highly coupled to the particle orientation, which itself is a function of the flow. This award will perform experiments, simulations, and theories to characterize the motion of non-spherical particles in polymeric fluids and quantify the coupling between the lift and orientation for different flow rates, particle geometries, fluid properties, and channel confinement. This information is valuable for processing rod-like and disk-like particles in viscoelastic suspensions in the applications mentioned above, as it provides design guidelines for the migration time and final location for different particle shapes.This study specifically will perform microfluidic experiments where one flows a dilute suspension of spheroids (prolate and oblate) through a tube. Different fluids and channel sizes will be used, allowing one to systematically vary the fluid properties and channel confinement. The particle’s 3D position and orientation distribution at different channel locations will be visualized using holography, allowing one to obtain long-time particle positions and rate of migration. Direct numerical simulations and theories will complement the studies, developing relationships for lift forces in this geometry as well as other geometries that are important for fluid characterization. Both investigators will create demos about complex fluids for Purdue’s Women in Engineering Program, as well as create similar exhibits for elementary school students at Imagination Station, a local science center. These exhibits will be run by undergraduates working in the respective labs and an honors engineering society advised by the investigators. Lastly, undergraduates from underrepresented communities will be recruited for research through Purdue’s SURF program.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.