CAREER: Free Surface Mobility and its Role in the Formation of Exceptionally Stable Glasses

职业：自由表面迁移率及其在形成异常稳定的玻璃中的作用

• 批准号: 1350044
• 负责人: Zahra Fakhraai
• 金额: $ 57.5万
• 依托单位: University of Pennsylvania
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-03-15 至 2019-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1350044&HistoricalAwards=false
• 关键词: CAREER; Free; Surface; Mobility; its

Technical SummaryMolecular glasses with high densities and exceptional kinetic stabilities have been recently produced by means of physical vapor deposition (PVD). In these experiments, the substrate temperature was held at a temperature below the glass transition temperature, Tg, where the bulk relaxation dynamics are extremely slow. In order for these PVD glasses to overcome the kinetic barriers preventing bulk glasses from reaching such near-equilibrium states at low temperatures, molecules must have access to enhanced mobility during vapor deposition. It is hypothesized that this enhanced mobility is caused by a layer of increased mobility close to the air interface. With support from the Solid State and Materials Chemistry program in the Division of Materials Research, this hypothesis will be tested by studying the dynamical properties of the surface of organic molecular glasses using a nanoparticle probe technique developed by the PI and others. The proposed improvements to this technique will allow simultaneous studies of the properties of the bulk glass and its free surface, making it an ideal method for investigating the correlation between surface properties and stable glass formation. This technique will be applied on a broad range of organic molecules to investigate whether this phenomena is universal for all glasses, or a chemical effect specific to particular molecular structures. These studies will be important in advancing our fundamental understanding of the glass transition phenomena. Non-Technical Summary: Glasses, out of equilibrium solids with structures that resemble that of equilibrium liquids, are ubiquitous in our daily life, and are widely used in the electronic and medical industries. Despite this, developing new useful glassy materials, or improving the properties of known glassy materials has proven to be difficult due to extremely slow molecular motion within the glass. For example, in order to make high-density glasses via aging, the process by which a glass naturally becomes more dense, one would have to wait a few hundred thousand years. A recent discovery, however, shows that glasses with highly desirable properties, such as increased density and stability, can be produced in a few hours. It is hypothesized that this is caused by the presence of a layer at the air/glass surface of most organic and polymeric glasses that is a few nanometers thick and behaves like a liquid rather than an out of equilibrium solid. Our proposed studies aim at understanding the origins of the liquid-layer and its effect on the structure of glasses. Understating the properties of the liquid-layer can help design and produce materials with improved properties for organic electronic, pharmaceutical, lubrication and coating technologies. Furthermore, we will combine these studies with educational efforts aimed at introducing concepts of glassy polymer dynamics and structure to a wide audience. Polymers are widely used in everyday life. Products such as bullet proof glass, silly putty and tires are examples of materials with similar design concepts, but widely varying properties. We will design experimental modules to highlight the importance of chemical composition, structure and dynamics on the final properties of a polymeric system. These experiments will be presented with adjustable levels of technical detail so that students of all backgrounds can learn from them. The PI will also work closely with institutions at the University of Pennsylvania and science teachers from elementary and high schools in the Philadelphia area to develop, implement, and disseminate these modules. To reach an even larger audience, videos of these modules will be made available online.

技术概述最近通过物理气相沉积（PVD）制备了具有高密度和优异动力学稳定性的分子玻璃。在这些实验中，衬底温度保持在低于玻璃化转变温度Tg的温度，其中体弛豫动力学极其缓慢。 为了使这些PVD玻璃克服阻止块体玻璃在低温下达到这种近平衡状态的动力学障碍，分子必须在气相沉积期间获得增强的迁移率。假设这种增强的移动性是由靠近空中接口的增加的移动性层引起的。在材料研究部门的固态和材料化学计划的支持下，这一假设将通过使用PI和其他人开发的纳米粒子探针技术研究有机分子玻璃表面的动力学特性来进行测试。对该技术的改进将允许同时研究大块玻璃及其自由表面的性质，使其成为研究表面性质和稳定玻璃形成之间的相关性的理想方法。这项技术将应用于广泛的有机分子，以研究这种现象是否对所有玻璃都是普遍的，或者是特定分子结构的化学效应。 这些研究将是重要的，在推进我们的玻璃化转变现象的基本理解。非技术总结：玻璃是一种非平衡固体，其结构类似于平衡液体，在我们的日常生活中无处不在，并广泛用于电子和医疗行业。尽管如此，开发新的有用的玻璃质材料，或改善已知玻璃质材料的性能已被证明是困难的，因为玻璃内的分子运动非常缓慢。例如，为了通过老化制造高密度玻璃，玻璃自然变得更致密的过程，人们必须等待几十万年。然而，最近的一项发现表明，具有高度理想特性的玻璃，如增加的密度和稳定性，可以在几个小时内生产出来。据推测，这是由于在大多数有机和聚合物玻璃的空气/玻璃表面存在一层，该层厚度为几纳米，并且表现得像液体而不是不平衡的固体。我们提出的研究旨在了解液体层的起源及其对玻璃结构的影响。 了解液体层的性质可以帮助设计和生产具有改进性能的材料，用于有机电子，制药，润滑和涂层技术。此外，我们将结合联合收割机这些研究与教育工作，旨在介绍玻璃态聚合物动力学和结构的概念，以广大观众。聚合物广泛应用于日常生活中。 防弹玻璃、橡皮泥和轮胎等产品都是具有类似设计概念但性能差异很大的材料。我们将设计实验模块，以突出化学组成，结构和动力学对聚合物系统的最终性能的重要性。这些实验将与技术细节的可调水平，使所有背景的学生可以从中学习。 PI还将与宾夕法尼亚大学的机构以及费城地区小学和高中的科学教师密切合作，开发，实施和传播这些模块。 为了让更多的人了解这些单元，将在网上提供这些单元的录像。