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

PI: Koch, Donald l .提案编号：1435013机构：康奈尔大学标题：使用形状来控制加工流程中粒子的方向和位置最近在易于制造具有控制形状的粒子方面的进展促进了对可以从这些粒子的组装中创建的材料范围的兴奋。虽然人们的注意力主要集中在形状对随机热运动引起的粒子聚集方式的影响上，但形状也可以对流体流动引起的结构产生令人惊讶的影响。直到最近，人们还认为所有轴对称的刚性颗粒都在粘性流体的剪切流动中连续旋转。然而，研究人员最近预测存在一类具有尖锐外缘的非旋转环状粒子。该项目将包括应用计算和理论技术来扩大流对准粒子形状的范围并探索其实用性。一个实验项目将探索制造粒子的方法，并观察它们的流动对准行为。基础研究将以具有特定力学，流变学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兼科学家的身份探索这些应用。本科研究人员将协助混沌动力学的理论研究和制造方法的发展。该研究的视觉吸引力将在当地儿童的K-12外展活动中得到利用。伊萨卡科学中心是美国的科学博物馆。采用边界元法（BEM）计算和细长体理论分析，探讨了刚性粒子在低雷诺数简单剪切流中的排列行为。边界元模拟将用于：(1)寻找在中等宽高比下最有效地停止旋转的截面形状；(2)探索中心填充环（以形成气体屏障）的可能性；(3)内外前后不对称环在流向状态下均表现出稳定的横流线漂移。针对环径厚比较大的环，将发展细长体理论（SBT）。这种SBT的一个新方面是需要确定环截面附近的速度梯度引起的每单位周长的力。这个交叉项没有出现在以前的粒子的圆形或椭圆形截面的SBT。SBT模拟将确定与其他环的流体动力学相互作用是否会诱导流对准环翻转，并确定具有横流漂移的粒子在接近壁面时达到的平衡位置。SBT计算还将用于探索轴对称的轻微偏差可能导致粒子在简单剪切流中经历混沌旋转和平移运动的可能性，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色散行为。非前后对称环流排列和显示横流漂移将采用光刻技术制造。为了制造前后对称的环，使其与流体运动对齐，研究人员将探索一种混合合成方法，该方法基于在微流控滴过程中产生环形颗粒，随后将颗粒嵌入薄膜中并拉伸以产生尖锐的环外缘。粒子的三维平移和旋转运动将在一个反向旋转的库埃特装置中观察到。稀释和半稀释悬浮液的流变学将被测量，以揭示由于流动排列而导致的粘度下降。

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.