CAREER: Dynamics and thermodynamics of ultra-strong glassformers

职业：超强玻璃形成剂的动力学和热力学

• 批准号: 2143815
• 负责人: Daniel Sussman
• 金额: $ 65.64万
• 依托单位: Emory University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-08-01 至 2027-07-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2143815&HistoricalAwards=false
• 关键词: CAREER; Dynamics; thermodynamics; ultra; strong

This award is funded in part under the American Rescue Plan Act of 2021 (Public Law 117-2).NON-TECHNICAL SUMMARYThis CAREER award supports an integrated program of theoretical research, computational study, and educational activity on a novel type of disordered solids, ``ultra-strong glasses''. What makes a material a solid? Crystalline materials have their atoms and molecules organized into neatly repeating patterns -- breaking up these repeating patterns costs energy, and the result is a material that resists deformation, that is, one that is solid. Glassy materials -- which can be made from silica as in ordinary window glass but also many other polymeric, molecular, or colloidal liquids -- are quite different: unlike orderly crystals their components are disordered, and their viscosity can vary enormously when their temperature is varied very slightly. These materials start out looking and behaving like a liquid but quickly become more and more sluggish as the temperature is decreased until, eventually, their motion is so imperceptible and the time for the molecules to flow around each other is so long that the whole system acts like a solid rather than a liquid.Almost all disordered materials follow two characteristic patterns for the precise way that their dynamics slow down, leading to a categorization of glasses as either "fragile" or "strong." Very recently there has been evidence of a third type of glass, an “ultra-strong” glass, whose dynamics and material properties would be much less sensitive to changing temperature than strong or fragile glasses. This unusual type of glass has, so far, been observed in two seemingly disconnected systems: computational models of dense epithelial tissue (tissue that covers all body surfaces and line body cavities) and of low-density vitrimers (a type of plastic material). At present there is no theoretical understanding of why these very different materials systems share similar glassy dynamics, or why either of them have properties so different from usual glassy materials in the first place.To understand this new class of materials -- which will itself help enable strategies for the design of new engineered materials with the unusual properties that the computational models suggest – the PI will embark on a systematic combination of extensive computational modeling together with an effort to build a theoretical description of ultra-strong glasses. At its core, this research seeks to address two primary questions: 1.) What is the fundamental nature of an ultra-strong glass? 2.) What features of a physical system lead to it?This project also supports educational and outreach activities that are closely integrated with the research project. The computational work involves large-scale numerical simulations, and the PI will develop Graphical User Interfaces that allow these research tools to be easily used in classes that are part of both the undergraduate and graduate curriculum. The PI and his research group will engage in community outreach activities, including mentorship activities at local schools and public science talks aimed at promoting awareness of the role STEM (Science, Technology, Engineering, and Mathematics) research plays in materials that appear in the everyday world around us. The PI, as part of his commitment to broadening participation of underrepresented groups in the physical sciences, will continue his work interacting with and mentoring students at a Minority Serving Institution, engaging those students in active research, and encouraging them to see themselves as future STEM professionals.TECHNICAL SUMMARYThis CAREER award supports theoretical and computational research on a novel class of disordered solids, ultra-strong glassformers. Ultra-strong behavior has recently been observed in two seemingly unrelated computational models: the PI's study of a coarse-grained model of dense biological tissue, and another group's study of low-density vitrimers. A primary research goal is to understand the origin of this anomalous type of disordered dynamics. The project will systematically explore numerical simulations of a family of related models at low temperature, using numerical analyses to test whether existing theories of glassy dynamics can make accurate predictions when confronted with data from these unusual systems. In this way, the underlying assumptions and validity of the approximations of many theories for glassy behavior can be probed; the focus of these tests will be on predicted connections between local structure, thermodynamics, and mechanics on the one hand and system dynamics on the other.An important quantity for characterizing a given glassy system (both intellectually, and in determining the functionality and processing of glasses as materials) is the fragility index. Until recently the fragility index characterized all glassy systems as either strong or fragile, corresponding to exponential or super-exponential scaling of the alpha relaxation time with inverse temperature. These categorizes also harmonize with recent theoretical work on mean-field models which describe the behavior of structural glasses in the infinite-dimensional limit, but this categorization is challenged by anomalous behavior of ultra-strong glasses and their remarkable, sub-exponential dependence of their alpha relaxation time with inverse temperature.There is no current understanding of what microscopic aspects of the models studied lead to this anomalous behavior, and thus it is unclear if ultra-strong glassforming ability can be found or engineered in a much broader class of physical systems. To address this need, the research will use large-scale simulations, extensive numerical analysis, and theoretical tools from the study of disordered solids to uncover the origin of ultra-strong behavior in the generalized class of vertex and Voronoi models of dense cellular matter. A fundamental set of model components that lead to this type of anomalous glassy behavior will be proposed, allowing for new ultra-strong glassformers to be identified and investigated.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.

该奖项部分由2021年美国救援计划法案（公法117-2）资助。该职业奖支持一项关于新型无序固体“超强玻璃”的理论研究、计算研究和教育活动的综合计划。是什么使物质成为固体？晶体材料的原子和分子组织成整齐的重复模式——打破这些重复模式需要消耗能量，结果是一种抗变形的材料，也就是说，一种固体材料。玻璃材料——它可以由普通窗玻璃中的二氧化硅制成，也可以由许多其他聚合物、分子或胶体液体制成——是完全不同的：与有序的晶体不同，它们的成分是无序的，当它们的温度发生很小的变化时，它们的粘度会发生很大的变化。这些材料开始看起来和行为都像液体，但随着温度的降低，它们很快变得越来越迟钝，直到最终，它们的运动是如此难以察觉，分子之间流动的时间是如此之长，以至于整个系统表现得像固体而不是液体。几乎所有无序的材料都遵循两种特征模式，即它们的动力学减慢的精确方式，导致玻璃被分类为“易碎”或“坚固”。最近有证据表明，第三种玻璃，一种“超强”玻璃，其动力学和材料性能对温度变化的敏感性远远低于坚固或易碎的玻璃。到目前为止，这种不寻常的玻璃已经在两个看似不相关的系统中被观察到：密集上皮组织（覆盖所有身体表面并排列体腔的组织）和低密度玻璃体（一种塑料材料）的计算模型。目前还没有从理论上理解为什么这些非常不同的材料系统具有相似的玻璃动力学，或者为什么它们中的任何一个具有与通常的玻璃材料如此不同的性质。为了理解这种新型材料——它本身将有助于设计具有计算模型所显示的不寻常特性的新工程材料的策略——PI将着手将广泛的计算模型与努力建立超强玻璃的理论描述相结合。在其核心，这项研究试图解决两个主要问题：1)超强玻璃的基本性质是什么？2)。物理系统的哪些特征导致了它？该项目还支持与研究项目密切相关的教育和推广活动。计算工作涉及大规模数值模拟，PI将开发图形用户界面，使这些研究工具易于在本科和研究生课程的课堂上使用。PI和他的研究小组将参与社区外展活动，包括在当地学校的指导活动和公共科学讲座，旨在提高人们对STEM（科学、技术、工程和数学）研究在我们日常生活中所扮演的角色的认识。作为他致力于扩大未被充分代表的群体参与物理科学的一部分，PI将继续与少数民族服务机构的学生进行互动和指导，让这些学生积极参与研究，并鼓励他们将自己视为未来的STEM专业人士。本职业奖支持对一类新型无序固体的理论和计算研究，即超强玻璃形成物。最近，在两个看似无关的计算模型中观察到了超强行为：PI研究的是致密生物组织的粗粒度模型，另一个小组研究的是低密度的玻璃体。一个主要的研究目标是了解这种异常类型的无序动力学的起源。该项目将系统地探索一系列相关模型在低温下的数值模拟，使用数值分析来测试现有的玻璃动力学理论是否可以在面对这些不寻常系统的数据时做出准确的预测。通过这种方式，可以探索许多玻璃态行为理论的基本假设和近似的有效性；这些测试的重点将放在局部结构、热力学和力学与系统动力学之间的预测联系上。表征一个给定的玻璃系统的一个重要的量（无论是在智力上，还是在确定玻璃作为材料的功能和加工过程中）是脆性指数。直到最近，脆性指数将所有玻璃系统表征为强或脆弱，对应于α弛豫时间与逆温度的指数或超指数标度。这些分类也与最近关于描述结构玻璃在无限维极限下行为的平均场模型的理论工作相一致，但是这种分类受到了超强玻璃的异常行为以及它们的α弛豫时间与逆温度的显著的亚指数依赖性的挑战。目前尚不清楚所研究模型的哪些微观方面导致了这种异常行为，因此尚不清楚是否可以在更广泛的物理系统中发现或设计超强玻璃形成能力。为了满足这一需求，该研究将使用大规模模拟、广泛的数值分析和来自无序固体研究的理论工具来揭示密集细胞物质的广义顶点类和Voronoi模型中超强行为的起源。将提出导致这种异常玻璃性行为的一组基本模型组件，从而允许识别和研究新的超强玻璃成形器。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。