Stress Testing Theories of the Glass and Jamming Transitions Using Hyperellipsoids

该奖项支持凝固过程、统计力学和计算机模拟领域的理论和计算研究和教育。给定的液体在冷却时是如何决定结晶还是形成像窗户玻璃一样的无序固体？这个问题仍然没有答案，并且是当前材料研究的主要焦点。玻璃的形成与干扰转变密切相关，即颗粒状物质（如沙子或咖啡豆）在被压缩时发生的凝固。虽然在过去的十年里，玻璃干扰转变的理论取得了很大的进展，但这些理论大多假设粒子是球形的。这是一个潜在的严重限制，因为现实世界中很少有玻璃状和颗粒状材料是由球形分子或颗粒组成的。该项目旨在通过开展一个连贯的研究项目，重点关注其对粒子非球性的依赖，从而提高我们对玻璃干扰过渡的认识。该研究将系统地将由模型椭球颗粒组成的玻璃状和堵塞系统的结构差异与颗粒形状和样品制备方案的差异联系起来。椭球粒子模型相对较低的计算成本将被用来探索比化学细节模型更广泛的相关参数空间。需要解决的关键问题是：(1)粒子各向异性的重要性是否随着空间维度的增加而降低？(2)椭球的干扰转变特性在多大程度上影响了它们的玻璃化转变？计划中的研究旨在最大限度地实现长期目标，即获得足够的物理理解水平，以开发具有可定制结构、机械和声学特性的颗粒状和玻璃状材料的预测设计原则。该奖项将资助一名博士生和一名本科生在颗粒和玻璃物理、统计力学和计算机模拟方面的培训。PI还将开发和传播“EllJam”，这是一款iPhone/iPad应用程序，可以说明二维椭球体的凝固物理。使用诸如颗粒长径比和压缩率等参数将允许用户发现和区分导致结晶固体和导致无序固体的参数值，从而发展一些基本的直觉，哪些因素控制凝固的结果。这个应用程序旨在吸引K-12学生和年轻研究人员的兴趣。该奖项支持凝固过程领域的理论和计算研究和教育，特别是玻璃干扰转变，统计力学和计算机模拟。虽然颗粒各向异性在控制玻璃和堵塞系统的宏观特性方面的重要性早已被认识到，但直到过去十年，廉价的高输出3D打印机的发展才使生产具有各种精确指定形状的颗粒成为可能。合成技术的进步使得胶体的形状控制和定向有序小分子玻璃的制备成为可能。在这段时间里，计算机已经变得足够强大，可以在很长的时间尺度上模拟非球面粒子的大型系统。虽然在过去的十年中，玻璃干扰转变的理论取得了很大的进展，但这些理论大多假设粒子是球形的，因此无法捕捉到粒子各向异性的影响。这是一个潜在的严重限制，因为现实世界中很少有玻璃状和颗粒状材料是由球对称的分子或颗粒组成的。PI将进行研究，通过粗粒度模拟和分析建模的连贯程序，系统地将由椭球粒子组成的玻璃状和堵塞系统的结构差异与粒子形状差异联系起来。PI还将“压力测试”最近发展的高维玻璃干扰过渡理论，以确定它们是否至少在由非球面粒子组成的系统中保持定性准确。具体来说，研究小组将首先开发一个平行分子动力学代码来模拟超椭球体。然后，它将进行模拟和分析工作，旨在确定耦合尺寸和粒子长径比相关效应如何影响干扰和热玻璃化转变。这些研究需要回答的关键问题是：(1)粒子各向异性是否随着空间维度的增加而变得不那么重要，粒子局部有序的趋势是否会下降？如果是，速度有多快？(2)椭球中干扰跃迁的特殊特征，更确切地说，随着粒子长径比趋于一致，干扰密度变得单一，在多大程度上影响了它们的热玻璃化转变？回答这些问题将有助于软物质理论社区的长期目标，即获得足够的物理理解水平，以开发具有可定制结构，机械和声学特性的颗粒状和玻璃状材料的预测设计原则。该奖项将资助一名博士生和一名本科生在颗粒和玻璃物理、统计力学和计算机模拟方面的培训。PI还将开发和宣传“EllJam”，这是一款iPhone/iPad应用程序，可以演示“2D椭球体”干扰物理。用户将能够选择系统大小、粒子长宽比和压缩率，然后观察椭球干扰如何随这些参数变化。用户还可以选择倾向于在二维中结晶的单分散系统和通常用于干扰研究的50:50双分散系统。这个应用程序应该感兴趣的K-12学生和年轻的研究人员。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

NONTECHNICAL SUMMARYThis award supports theoretical and computational research and education in the fields of solidification processes, statistical mechanics, and computer simulations. How does a given liquid decide whether to crystallize or to form a disordered solid like window glass when it is cooled? This question remains unanswered, and is a principal focus of current materials research. Glass-formation is closely related to the jamming transition, the solidification of a granular material, like sand or coffee beans, that occurs when it is compressed. Although great advances in theories of the glass-jamming transition have been made over the past decade, most of these theories assume particles are spherical. This is a potentially serious limitation because very few real-world glassy and granular materials are composed of spherical molecules or grains.This project aims to advance our knowledge of the glass-jamming transition by conducting a coherent research program that focuses upon its dependence on particle asphericity. The research will systematically relate differences in the structure of glassy and jammed systems composed of model ellipsoidal particles to differences in particle shape and sample preparation protocol. The relatively low computational cost of the ellipsoidal-particle model will be exploited to explore relevant parameter spaces far more broadly than is feasible for chemically-detailed models. Key questions to be addressed are: (1) Does the importance of particle anisotropy decrease as spatial dimension increases? and (2) To what extent do the peculiar features of ellipsoids’ jamming transitions influence their glass transitions? The planned studies are designed with the aim to contribute maximally to the long-term goal of obtaining a level of physical understanding sufficient to develop predictive design principles for granular and glassy materials with tailorable structural, mechanical, and acoustic properties. This award will fund the training of one PhD student and one undergraduate student in granular and glass physics, statistical mechanics, and computer simulations. The PI will also develop and disseminate “EllJam”, an iPhone/iPad app that illustrates the solidification physics of 2D ellipsoids. Playing with parameters such as the particle aspect ratio and compression rate will allow the user to discover and distinguish parameter values leading to crystalline solids from those which lead to disordered solids, and hence to develop some basic intuition for which factors control the outcome of solidification. This app is intended to capture the interest of K-12 students and young researchers. TECHNICAL SUMMARYThis award supports theoretical and computational research and education in the fields of solidification processes, specifically, the glass-jamming transition, statistical mechanics, and computer simulations. While the importance of particle anisotropy in controlling macroscopic properties of glassy and jammed systems has long been recognized, it is only within the past decade that the development of cheap high-output 3D printers has allowed production of grains with a wide variety of precisely specified shapes. Advances in synthesis techniques have allowed comparable shape control for colloids as well as preparation of orientationally-ordered small-molecule glasses. Over this time, computers have become powerful enough to simulate large systems of aspherical particles over long timescales. Although great advances in theories of the glass-jamming transition have been made over the past decade, most of these theories assume particles are spherical and hence cannot capture the effects of particle anisotropy. This is a potentially serious limitation because very few real-world glassy and granular materials are composed of spherically symmetric molecules or grains.The PI will carry out studies that will systematically relate differences in the structure of glassy and jammed systems composed of ellipsoidal particles to differences in particle shape via a coherent program of coarse-grained simulations and analytic modeling. The PI will also “stress-test” recently developed high-dimensional theories of the glass-jamming transition by determining whether they remain at least qualitatively accurate for systems composed of aspherical particles. Specifically, the research team will first develop a parallel molecular dynamics code for simulating hyperellipsoids. Then it will conduct simulations and analytic work aimed at determining how coupled dimension and particle-aspect-ratio-dependent effects influence both jamming and the thermal glass transition. Key amongst the questions to be answered by these studies are: (1) Does particle anisotropy become less important as spatial dimension increases and the tendency of particles to locally order decreases — and if it does, how rapidly? and (2) To what extent do the peculiar features of jamming transitions in ellipsoids, more precisely jamming densities that become singular as the aspect ratio of a particle approaches unity, influence their thermal glass transitions? Answering these questions will contribute to the soft matter theory community’s long-term goal of obtaining a level of physical understanding sufficient to develop predictive design principles for granular and glassy materials with tailorable structural, mechanical, and acoustic properties. This award will fund the training of one PhD student and one undergraduate student in granular and glass physics, statistical mechanics, and computer simulations. The PI will also develop and publicize “EllJam”, an iPhone/iPad app that illustrates’ 2D ellipsoids’ jamming physics. The user will be able to choose the system size, the particle aspect ratio, and the compression rate, and then watch how ellipsoid jamming varies with these parameters. The user will also be able to choose between monodisperse systems which tend to crystallize in 2D and the 50:50 bidisperse systems typically employed in jamming studies. This app should be of interest to both K-12 students and young researchers.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.