Fluids: Jamming and Singular Flows

本项目研究：(1)过冷液体和玻璃；(2)流体界面上出现的奇点。这项工作的动机是不同材料可能变得卡住或僵硬的方式之间潜在相似的可能性。这项工作研究了经历玻璃化转变为无定形固体的液体与宏观的非热系统之间的相似性，宏观的非热系统是这样一种颗粒材料，它被挤入一种构型，也具有屈服应力。通过对液体的模拟和实验，我们将探索一个“干扰相图”，它统一了这两个看似不相交的转变，以确定降低温度产生的干扰是否类似于降低应力产生的干扰。还将对力链的形成进行调查。液体表面奇点将通过高速摄影来探测，以检查当液滴分裂成两个独立部分时界面上出现的奇点。将使用选择性退出的几何学来研究喷嘴的形成本身。将探索包覆颗粒的可能应用。参与这项研究的学生将接受关于高度跨学科的科学主题的新仪器和测量的出色培训。许多不同的材料被卡住，无法移动。这种堵塞可以在工厂中流经管道和料斗的颗粒状物质中观察到。当分子液体冻结成无定形状态时，也可以在玻璃形成的背景下看到这一点。这项研究旨在探索这两种看似不同类型的转换实际上可能相互关联的方式，它们具有相似的潜在物理机制，导致运动停止。这种潜在原因的发现将对各种科学和技术问题产生重要影响。将使用计算机模拟和实验来探索这些干扰转变。当一滴液体从较大的流体中脱落时，流体流动中的奇点是很重要的。在这一点上，由于流动的奇异性，对对象的简单数学描述就失效了。高速摄影研究将探索这种奇点的本质。还将使用选择性退出的几何学来研究喷嘴的形成。将探索将这一现象用于包覆颗粒，包括用于医疗应用的细胞。参与这项研究的学生将接受关于高度跨学科的科学主题的新仪器和测量的出色培训。

This project investigates : (1) supercooled liquids and glasses and (2) singularities appearing in fluid interfaces. The work is motivated by the possibility of an underlying similarity between the ways in which different materials can become jammed, or rigid. This work studies similarities between a liquid undergoing a glass transition into an amorphous solid, with a yield stress, and a macroscopic, athermal, system, such a granular material, which becomes jammed into a configuration, also with a yield stress. A "jamming phase diagram", which unifies these two seemingly disjoint transitions, will be explored using simulations and experiments on liquids to see if jamming produced by lowering temperature is similar to jamming produced by lowering the stress. There will also be an investigation of force-chain formation. Liquid surface singularities will be probed via high-speed photography to examine the singularity in the interface occurring when a drop splits into two separate pieces. The spout formation itself will be studied using the geometry of selective withdrawal. Possible applications for coating particles will be explored. The students involved in this research will receive excellent training with novel instruments and measurements on highly interdisciplinary scientific topics. %%%Many different materials become jammed so that they cannot move. Such jamming can be observed in granular material flowing through conduits and hoppers in a factory. It can also be seen in the context of glass formation when a molecular liquid is frozen into an amorphous state. This research is aimed at exploring the ways in which these two seemingly disparate types of transitions may in fact be related to each other with similar underlying physical mechanisms at work to cause the cessation of motion. The discovery of such an underlying cause would have important implications for a variety of scientific and technological problems. Both computer simulations and experiments will be used to explore these jamming transitions. Singularities in fluid flow are important whenever a drop of liquid breaks off from a larger body of fluid. At such a point a simple mathematical description of the object breaks down because of the singular nature of the flows. High-speed photographic studies will probe the nature such singularities. There will also be a study of the spout formation using the geometry of selective withdrawal. The use of this phenomenon for coating particles, including cells for medical applications, will be explored. The students involved in this research will receive excellent training with novel instruments and measurements on highly interdisciplinary scientific topics.