Understanding microscopic dynamics in sheared highly polydisperse soft materials

该奖项是对软材料如何流动的实验和计算研究。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：在同一样本中含有不同大小混合颗粒的液体。显微镜是用来观察流动样品中颗粒的轨迹的。这些观察将被用来发展关于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。研究人员将定期组织来访学生(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。该奖项的目的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。要研究的主要样本是高度分散的乳液，其中最大的液滴是最小液滴半径的十倍；以及模拟这些乳液的计算模型。用视频和共聚焦显微镜研究流动和剪切的样品，目的是长时间同时跟踪单个液滴。这些轨迹将根据位移的大小、相邻液滴的相对运动以及可能在样品流动时触发的级联重排来表征。对计算数据也将进行类似的分析。这些微观观察将与宏观流变学特性相联系。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。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 award is an experimental and computational study of how soft 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 mixture of sizes in the same sample. Microscopy is used to view the trajectories of particles in a flowing sample. These observations will be used to develop basic ideas about the flow of disordered materials, which will lead to better understanding of how to move, mix, and process complex materials of industrial relevance. The researchers will 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 award is to understand how amorphous solids flow, in particular to connect particle-scale rearrangements to macroscopic flow profiles and rheological behavior. The main samples to be studied are highly polydisperse emulsions, where the largest droplets are ten times the radius of the smallest droplets; and computational models that mimic these emulsions. Flowing and sheared samples are studied with video and confocal microscopy with a goal of simultaneous tracking of individual droplets for long times. These trajectories will be characterized in terms of magnitudes of displacements, relative motions of neighboring droplets, and cascading rearrangements that might be triggered as the sample flows. Similar analysis will be done for the computational data. These microscopic observations will be connected to macroscopic rheological properties. 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. 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.