Flow of colloids and emulsions: Microscopic details of rearrangements and stresses

1336401圆周率：在这个项目中，圆周率和他的实验室小组将研究软材料的流动，特别是乳状液(水中的油滴)。其目标是将流动乳液的微观细节与其宏观性质联系起来。该项目有两个推力：第一，研究稠密三维乳状液的剪切；第二，研究稠密二维乳状液的流动特性。3D样品将使用共聚焦显微镜进行观察。对于这些3D样本，将使用液滴大小变化高达一个数量级的样本来检查多分散性的重要性。这些高度分散的样品的流动在性质上不同于较少的多分散情况，来自该项目的数据将是理解高度分散的堵塞材料的基础。对于2D样品，油滴将被限制在两个平行的玻璃板之间，从而使液滴变形为圆形的准二维圆盘。根据液滴的轮廓和对其表面张力的了解，将测量液滴对之间的力，并与液滴流动时的重排有关。这些测量使流动的无定形材料的理论得以检验。微流控技术将被用来制造油滴，允许仔细控制液滴的大小、粘度和表面张力。软堵塞的材料很常见，包括胶状糊状物(如牙膏)、凝胶(如明胶)、泡沫(如剃须膏)和乳状液(如蛋黄酱)。与水等常规液体相比，人们对这些材料的流动特性了解较少。例如，由油滴组成的乳状液在水中的流动必须涉及单个液滴的重新排列；此外，液滴可以拉伸甚至破裂，从而使流动更加复杂。由该奖项资助的项目将使用显微镜拍摄流动的乳状液的电影，以观察油滴如何运动，以及这些运动如何与流动所需的力有关。这将使我们更好地了解如何创建具有特定流动特性的乳液，以及如何更好地在工业中加工乳液。此外，威克斯教授每年至少为小学生小组进行一次到实验室的实地考察。这些学生将研究“粘性”材料的特性，例如本项目中使用的油和水乳状液。虽然这样的材料很常见，也很安全，但它们也违反了直觉，会让学生产生好奇心。比如，剃须膏可以堆在桌子上，而肥皂水的水坑必须平放。这种材料挑战了学生们认为材料只能以固体、液体或气体的形式出现的想法。

1336401 PI: WeeksIn this project, the PI and his lab group will study the flow of soft materials, in particular emulsions (oil droplets in water). The goal is to connect the microscopic details of the flowing emulsions to their macroscopic properties. The project has two thrusts: first, to study the shear of dense three-dimensional emulsions; and second, to investigate the flow properties of dense two-dimensional emulsions. The 3D samples will be viewed using confocal microscopy. For these 3D samples, the importance of polydispersity will be examined using samples with droplet sizes that vary by as much as an order of magnitude. Flow of these highly polydisperse samples is qualitatively distinct from less polydisperse cases, and the data from this project will be a foundation to understand jammed materials that are highly polydisperse. For the 2D samples, the oil droplets will be confined between two parallel glass plates, so that the droplets are deformed into round quasi-two-dimensional disks. From the outlines of the droplets and knowledge of their surface tension, forces between droplet pairs will be measured and related to the rearrangements as the droplets flow. These measurements enable testing of theories of flowing amorphous materials. Microfluidic techniques will be used to create the oil droplets, allowing careful control over droplet sizes, viscosities, and surface tension. Soft jammed materials are common, and include colloidal pastes (such as toothpaste), gels (such as gelatin), foams (such as shaving cream), and emulsions (such as mayonnaise). In contrast to regular liquids like water, the flow properties of these materials are less well understood. For example, the flow of an emulsion composed of oil droplets in water must involve rearrangements of individual droplets; additionally, the droplets can be stretched and even break up, making the flow even more complicated. The projects funded by this award will use microscopes to take movies of flowing emulsions, to see how the oil droplets move and how these motions are related to the forces required to flow them. This will lead to better understanding of how to create emulsions with specific flow properties, and how to better process emulsions in industry. Additionally, Professor Weeks will conduct at least one field trip each year to his laboratory for groups of primary school students. These students will investigate the properties of "squishy" materials such as the oil-and-water emulsions used in this project. While such materials are common and safe, they are also counterintuitive and get students curious. For example, consider shaving cream, which can sit in a pile on a table, in contrast to a puddle of soapy water which must lie flat. Such materials challenge the ideas students have that materials only come as solids, liquids, or gases.