The Effect of Particle-polymer Interactions on the Rheology and Structure of Dilute Particle-filled Polymeric Liquids

聚合物分子和悬浮固体颗粒的溶液用于从油漆和涂料到医疗保健和食品的一系列产品中。 聚合物分子和悬浮颗粒协同作用，产生一系列影响其加工的复杂流体行为。 虽然人们对颗粒和聚合物如何独立地改变流体反应知之甚少，但对它们的耦合效应知之甚少。 该项目将开发理论来预测1）由颗粒引起的流动扰动引起的聚合物分子的拉伸和排列，2）细长固体颗粒或纤维如何在聚合物存在下排列，以及3）颗粒和聚合物混合物的流动响应。 流速，流动历史，和流动的几何形状上的聚合物颗粒混合物的行为的影响将被检查。 作为这项研究的一部分，一名研究生和几名本科生将接受流体动力学和理论及数值方法的培训。主要研究者和研究生都将参与指导一名本科生，该学生来自STEM领域代表性不足的一个小组。将在稳定剪切、振荡剪切和聚合物溶液中球体和纤维悬浮液的拉伸流变学中探索颗粒和聚合物应力的相互作用。 颗粒的流体动力学扰动可以显著地改变周围流体中的聚合物构象，而聚合物应力可以导致颗粒应力波的意外变化。 纤维悬浮液的流变性受纤维取向的强烈影响。虽然以前的理论研究表明，聚合物应力诱导纤维与稳定的简单剪切流的涡度轴对齐，实验表明，即使在低颗粒浓度的取向更大的多样性。 本文将研究简单剪切流中纤维的稳定固定取向及其对流体流变特性的依赖性。 稀颗粒填充的聚合物液体的流变学将使用系综平均方程方法来确定。 为了便于准分析结果，将进行基于小聚合物浓度的扰动分析。 与以前的研究，认为二阶流体，这种方法允许探索的应变率（或德博拉数）的流变学的依赖性，即使在考虑弱聚合物应力。 在贴体坐标系中使用有限体积法的完全非线性计算将补充简单剪切流中纤维取向的理论研究。 包括和排除剪切稀化和有限延伸性的各种流变模型将用于理解不同聚合物流变特性对颗粒-聚合物相互作用的影响。 为了扩大该领域未来研究生的多样性，项目的PI和研究生将提供-在另一所大学的未来女性或URM学生的整个本科生涯中进行指导，并提供复杂流体的本科研究项目。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准。

Solutions of polymer molecules and suspended solid particles are used in a range of products from paints and coatings to health care and foods. The polymer molecules and the suspended particles act cooperatively to create a range of complex fluid behaviors that impact their processing. While much is known about how particles and polymers act independently to alter fluid responses, little is known about their coupled effects. This project will develop theories to predict 1) the stretching and alignment of polymer molecules by the disturbance to the flow caused by the particles, 2) how elongated solid particles or fibers align in the presence of polymers, and 3) the flow response of mixtures of particles and polymers. The influence of flow rate, flow history, and flow geometry on the behavior of polymer-particle mixtures will be examined. As part of this research, a graduate student and several undergraduates will receive training in fluid dynamics and theoretical and numerical methods. Both the principal investigator and the graduate student will participate in mentoring an undergraduate student from a group that is underrepresented in STEM fields.The interplay of particle and polymer stresses will be explored in steady shear, oscillatory shear, and extensional rheology of suspensions of spheres and fibers in polymer solutions. The hydrodynamic disturbance of the particles can dramatically alter the polymer conformation in the surrounding fluid while the polymer stress can lead to unexpected changes in the particle stresslet. The rheology of fiber suspensions is strongly influenced by the orientations of the fibers. While previous theoretical studies have suggested that polymer stresses induce fiber alignment with the vorticity axis of a steady simple shear flow, experiments reveal a greater diversity of orientations even at low particle concentrations. A search will be made for stable fixed orientations of fibers in simple shear flow and the dependence of the orientations on the rheological properties of the fluid. The rheology of dilute particle-filled polymeric liquids will be determined using an ensemble averaged equation approach. To facilitate quasi-analytic results, perturbation analyses based on small polymer concentration will be performed. In contrast to previous studies that considered second-order fluids, this approach allows an exploration of the strain rate (or Deborah number) dependence of the rheology even while considering weak polymeric stresses. Fully nonlinear computations using a finite volume method in a body-fitted coordinate system will complement the theoretical studies of fiber orientation in simple shear flow. A variety of rheological models that include and exclude shear thinning and finite extensibility will be used to understand the effect that different polymer rheological properties have on particle-polymer interactions. To broaden the diversity of future graduate students in the field, the PI and graduate student on the project will provide on-going mentorship throughout the undergraduate career of a prospective female or URM student from another university as well as offering undergraduate research projects on complex fluids.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.