Using shape to control the orientations and positions of particles in processing flows

PI：Koch，Donald L.建议编号：1435013机构：康奈尔大学标题：使用形状控制加工流程中颗粒的方向和位置最近在制造形状可控颗粒的简易性方面的进展促进了人们对可由此类颗粒组装而成的材料范围的兴奋。虽然人们的注意力主要集中在形状对随机热运动导致的颗粒聚集方式的影响上，但形状也可能对流体流动引起的结构产生令人惊讶的后果。直到最近，人们还认为所有轴对称的刚性颗粒在粘性流体的剪切流中都是连续旋转的。然而，研究人员最近预测，存在一类具有锋利外缘的非旋转环状粒子。该项目将包括计算和理论技术的应用，以扩大流动对准颗粒形状的范围并探索其实用性。一个实验计划将探索制造颗粒的方法，并观察它们的流动对准行为。基础研究将以具有特定机械、流变性或渗透性的材料的各种目标应用为指导。参与研究的学生将被鼓励以发明家的身份探索这些应用。本科生研究人员将帮助混沌动力学的理论研究和制作方法的发展。这项研究的视觉吸引力将在当地儿童-S科学馆-伊萨卡科学中心的K-12推广活动中得到利用。将使用边界元计算和细长体理论分析来探索排列在低雷诺数简单剪切流中的刚性粒子的行为。边界元模拟将被用于：(1)搜索在中等长宽比下最有效地阻止旋转的横截面形状；(2)探索具有填充中心(以提供气体屏障)的环可以流动对齐的可能性；以及(3)显示具有输入-输出和前后不对称的环在其流动对齐状态下表现出稳定的横向流线漂移。对于直径与厚度比较大的环，将发展细长体理论(SBT)。这种SBT的一个新的方面是需要确定由环横截面附近的速度梯度引起的单位周向力。对于具有圆形或椭圆形横截面的粒子，该交叉项在以前的SBT中没有出现过。SBT模拟将确定流动对准环是否可以通过与其他环的流体动力相互作用而翻转，并确定具有横流漂移的颗粒在接近壁面时到达的平衡位置。SBT计算还将被用来探索这样一种可能性，即略微偏离轴对称可能导致粒子在简单剪切流中经历混沌的旋转和平移运动，从而在没有布朗运动或粒子-粒子相互作用的情况下导致自弥散行为。将使用光刻技术制造流动对准并表现出横流漂移的非前后对称环。为了制造出与流体运动对齐但平移的前后部对称环，研究人员将探索一种混合合成方法，这种合成方法是在微流控液滴过程中产生环形颗粒，然后将颗粒嵌入薄膜中并拉伸，以产生环的尖锐外缘。粒子的三维平移和旋转运动将在反向旋转的Couette装置中观察到。将测量稀释和半稀释悬浮液的流变性，以揭示由于流动对齐而导致的粘度降低。

PI: Koch, Donald L.Proposal Number: 1435013Institution: Cornell UniversityTitle: Using shape to control the orientations and positions of particles in processing flowsRecent advances in the ease of fabricating particles with controlled shape have fostered excitement about the range of materials that can be created from assemblies of such particles. While attention has focused primarily on the influence of shape on the manner in which particles assemble due to random thermal motion, shape can also have surprising consequences for structure induced by fluid flows. Until recently, it had been thought that all axisymmetric, rigid particles rotated continuously in shear flows of viscous fluids. However, the investigators recently predicted the existence of a class of non-rotating ring-shaped particles with sharp outer edges. This project will include the application of computational and theoretical techniques to expand the range of flow-aligning particle shapes and explore their utility. An experimental program will explore methods to fabricate the particles and observe their flow aligning behavior. The fundamental studies will be guided by various target applications for materials with specific mechanical, rheological or permeability properties. The students involved in the research will be encouraged to explore these applications as inventor-scientists. Undergraduate researchers will aid with theoretical studies of chaotic dynamics and with the development of fabrication methods. The visually appealing nature of the research will be exploited in K-12 outreach activities at a local children?s science museum, the Ithaca Sciencenter.The behavior of rigid particles that align in a low Reynolds number simple shear flow will be explored using boundary element method (BEM) computations and slender-body theory analysis. BEM simulations will be used to: (1) Search for cross-sectional shapes that are most effective in stopping rotation at moderate aspect ratios; (2) Explore the possibility that a ring with a filled center (to impart a gas barrier) can flow align; and (3) Show that rings with both in-out and fore-aft asymmetry exhibit a steady cross-streamline drift in their flow-aligned state. Slender-body theory (SBT) will be developed for rings with a large ratio of ring diameter to thickness. A novel aspect of this SBT is the need to determine the force per unit circumference induced by the velocity gradient near the ring cross-section. This cross term has not appeared in previous SBT for particles with circular or elliptical cross-sections. SBT simulations will determine whether flow-aligning rings can be induced to flip by hydrodynamic interactions with other rings and to determine the equilibrium position a particle with cross-stream drift reaches as it approaches a wall. SBT calculations will also be used to explore the possibility that slight deviations from axisymmetry can lead to particles that undergo chaotic rotational and translational motions in a simple shear flow, leading to a self-dispersive behavior in the absence of Brownian motion or particle-particle interactions. Non-fore-aft symmetric rings that flow-align and exhibit cross-stream drift will be fabricated using photolithography. To produce fore-aft symmetric rings that align but translate with the fluid motion, the investigators will explore a hybrid synthesis based on producing toroidal particles in a microfluidic drop process and subsequently embedding the particles in a film and stretching to create the sharp outer edge of the ring. The three-dimensional translational and rotational motion of the particles will be observed in a counter-rotating Couette device. The rheology of dilute and semi-dilute suspensions will be measured to reveal the decrease in viscosity due to flow alignment.