Probing Glassy and Granular Physics in a Model Soft Glassy Material

非技术摘要：软玻璃材料(SGM)含有密集聚集在周围液体中的微小颗粒，我们周围都可以看到这样的例子：肥皂含有拥挤的气泡，蛋黄酱充满油滴，牙膏充满固体磨料。SGM通常是粘稠的固体，具有共同的相当不寻常的机械特性，其物理起源尚不清楚，例如当它们变形时，往往会急剧软化，然后极慢地重新变硬。这个项目将对一种水包油乳状液进行深入研究，这种乳状液被设计成透明的--本质上是透明的蛋黄酱--使用最先进的显微镜来制作单个液滴在变形、软化和重新硬化过程中重新排列的三维电影。实际重排事件的3-D电影将与相应的模拟进行比较，以测试事件及其触发因素与目前未经验证的理论预测的关系。由于这些材料的性质无处不在，该项目有可能影响许多实际问题，从食品和化妆品加工和配方到提高石油采收率的改进战略。这项工作引人注目的视觉本质将促进费城公立学校对高中生的推广工作。技术摘要：软玻璃材料(SGM)一词描述了一组无处不在的材料，包括浓缩乳、泡沫和浆料，它们位于软凝聚态物理中两个突出问题的交叉点：胶体玻璃转变和颗粒堵塞转变。由于在这些典型的不透明或混浊的材料中实验探测微观动力学的困难，SGM仍然非常神秘。该项目将直接测试SGM中的流动和松弛模型，包括软玻璃流变学模型，使用通过粗化流态化的折射率和密度匹配的乳状液的三维共聚焦成像。通过在类似于气泡动力学的模拟环境中复制观察到的结构，然后可以对每个结构进行多次变形“实验”，以识别和表征微观液滴重排的微妙应变和能量障碍。对这一模型体系的深入理解将进一步加深对胶体玻璃和颗粒材料的理解。数据的丰富、可视的本质及其与日常材料--肥皂泡沫--的联系，将有助于费城公立学校的高中生开展推广活动，同时为研究生和本科生提供最先进的三维显微镜实践体验。

Non-technical Abstract:Soft Glassy Materials (SGMs) contain microscopic particles densely crowded together in a surrounding liquid and examples are found all around us-- soap suds contain crowded air bubbles, mayonnaise is filled with oil droplets, and toothpaste is filled with solid abrasives. SGMs are generally squishy solids that have in common rather unusual mechanical properties whose physical origins are poorly understood, such as the tendency to soften dramatically when they're deformed, followed by extremely slow re-stiffening afterwards. This project will perform an intensive study of an oil in water emulsion engineered to be transparent -- essentially clear mayonnaise-- using state of the art microscopy to make three dimensional movies of individual droplets rearranging during deformation, softening and re-stiffening. The 3-D movies of actual rearrangement events will be compared with corresponding simulations to test the events and their triggers relative to the predictions of currently untested theories. Because of the ubiquitous nature of these materials, this project has the potential to impact numerous practical problems ranging from food and cosmetic processing and formulation to improved strategies for enhanced petroleum recovery. The arresting visual nature of the work will facilitate outreach efforts to high-school students in the Philadelphia public schools.Technical Abstract:The term 'Soft Glassy Material' (SGM) describes an ubiquitous set of materials including concentrated emulsions, foam and pastes that lay at the intersection of two outstanding problems in soft condensed matter physics: the colloidal glass transition and the granular jamming transition. SGMs remain deeply mysterious due the difficulty of experimentally probing the microscopic dynamics in these typically opaque or turbid materials. This project will directly test models for flow and relaxation in SGMs, including the Soft Glassy Rheology model, using three-dimensional confocal imaging of an index- and density-matched emulsion that is fluidized by coarsening. By replicating the observed structures in a simulation environment similar to Bubble Dynamics, multiple deformation 'experiments' on each structure can then be performed to identify and characterize the subtle strain and energy barriers for microscopic droplet rearrangements. A deep understanding in this model system will further understanding in colloidal glasses and granular materials. The rich, visual nature of the data and its association with an everyday material-- soap foam--will facilitate outreach efforts to high-school students in the Philadelphia public schools, while providing graduate and undergraduate students hands-on experience with state of the art three-dimensional microscopy.