Deformation and flow of highly polydisperse amorphous solids

这是一项关于无序物质如何流动的实验研究。泥浆、水泥、泡沫和泥土等物质在滑坡中的流动与液体的流动有很大不同。这些材料以前曾被研究过，但它们的复杂性使人们很难确定这些有趣的物质如何流动的一般原理。过去的一些研究试图使用简单的系统来模拟这些复杂的材料：标准的简单系统是充满特定尺寸的圆形颗粒的液体。很明显，这些简单的系统无法再现真实材料的许多有趣的流动行为。这项工作研究中等复杂程度的材料的流动：同一样本中含有各种大小颗粒的液体。光学显微镜被用来检查粒子的运动并观察它们是如何重新排列的，例如，小粒子是如何被迫围绕大粒子运动的。这些观察将被用来发展关于其他无序材料流动的基本想法，这将导致更好地理解如何移动、混合和处理与工业相关的复杂材料。本科生和研究生将从事这项研究。此外，研究人员定期组织来访学生(从一年级到高中)进行实地考察，向他们传授软而柔软的材料以及科学家如何研究这些材料。该项目的目标是了解无定形固体如何流动，特别是将颗粒尺度重排与宏观流动特征和流变行为联系起来。样品是高度分散的乳液，其中最大的液滴是最小液滴半径的十倍(或更多)。用视频和共聚焦显微镜研究了流动样品和剪切样品。这使得能够测量单个液滴的运动。当施加大应变时，液滴不可逆地重新排列。这些重排可以根据拓扑变化、位移的大小以及流动的局部非仿射程度来量化。该项目将液滴重排的这些细节与单个液滴的大小联系起来。更广泛地说，这些细节可能取决于整体液滴尺寸分布。此外，微观细节必须与宏观流变特性相联系。可以对固体颗粒进行补充实验，模拟提供了探索这些问题的第三条途径。总体动机是为了弥合先前研究大小相当相似的颗粒混合物的模型系统与复杂的现实世界材料(如泥浆和水泥)之间的差距。这将对大尺寸多分散性非晶态材料的剪切有新的微观认识。至少有一名本科生和一名研究生将参与这项研究。研究团队还将每年举办实地考察，向来访的学生证明，可以用简单的材料来完成尖端科学，他们可以真正拿到手。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This is an experimental study of how disordered materials flow. The flow of materials like mud, cement, foam, and dirt in landslides is quite different from the flow of liquids. These materials have been studied before but their complexity makes it difficult to determine general principles about how these interesting substances flow. Some past studies used simple systems to try to mimic these complicated materials: a standard simple system is a liquid full of round particles with a specific size. It is clear that these simple systems fail to reproduce many of the interesting flow behaviors of the real materials. This work studies the flow of materials with intermediate complexity: liquids with particles with a wide variety of sizes in the same sample. Optical microscopy is used to examine the motion of the particles and see how they rearrange, for example, how small particles are forced to move around large particles. These observations will be used to develop basic ideas about the flow of other disordered materials, which will lead to better understanding of how to move, mix, and process complex materials of industrial relevance. Undergraduate and graduate students will be engaged in conducting the research. Additionally, the researchers regularly host field trips of visiting students (first grade through high school) to teach them about soft squishy materials and how scientists study these materials.The objective of this project is to understand how amorphous solids flow, in particular to connect particle-scale rearrangements to macroscopic flow profiles and rheological behavior. The samples are highly polydisperse emulsions, where the largest droplets are ten times the radius of the smallest droplets (or more). Flowing and sheared samples are studied with video and confocal microscopy. This enables the motion of individual droplets to be measured. When a large strain is applied, droplets rearrange irreversibly. These rearrangements can be quantified in terms of topological changes, magnitudes of displacements, and how non-affine the flow is locally. The project connects these details of droplet rearrangements to the size of individual droplets. More broadly, these details likely depend on the overall droplet size distribution. Additionally, the microscopic details must connect with macroscopic rheological properties. Complementary experiments can be done with solid particles, and simulations provide a third route to explore these questions. The overall motivation is to bridge the gap between prior model systems that studied mixtures of particles of fairly similar sizes, and complex real-world materials such as mud and cement. This will lead to new microscopic understanding of the shear of amorphous materials with large size polydispersity. At least one undergraduate and one graduate student will be involved with the research. The research team will also host field trips each year to demonstrate to visiting students that cutting edge science can be done with simple materials which they can literally get their hands on.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.