CAREER: Glass formation in strongly interacting polymers - predictive understanding from high-throughput simulation and theory

本职业奖支持软材料的理论和计算研究以及教育。从在室温下保持活力的疫苗，到灵活稳定的太阳能电池和电子产品，各种转型技术都在等待着新聚合物材料的开发，这种材料是由具有重复分子单元的长分子链制成的柔软材料，可以推动材料性能的极限。在这些新技术中，许多最有前途的材料都有两个共同的特点：通过玻璃化转变的过程，它们不会形成晶体而凝固；它们的分子之间有很强的相互作用。与此同时，这些特性是这些材料潜力的关键，它们也对合理的材料设计提出了挑战。玻璃化转变是这些材料性质的主要决定因素，对其物理学的基本理解仍然缺乏。这个问题在强相互作用的聚合物中尤其严重，因为强相互作用对标准理论方法是有抵抗的，并且很难在计算机模拟中有效地捕获。因此，不可能在足够长的时间尺度和足够多样化的化学中研究分子行为，从而揭示这些材料的基本物理特性并指导它们的设计。该项目旨在克服这些挑战。PI将结合新的理论方法和改进的策略来模拟玻璃形成材料，为强相互作用的玻璃形成聚合物建立基本的见解和设计指南。这一策略将使我们能够访问非常长的时间尺度和数以万计的化学物质，以确定这些材料分子物理的共同方面，并将其转化为预测其性质的理论。这种理论的理解，反过来，将指导分子结构的选择，产生独特的，有针对性的材料特性。该项目的成功将有助于加速材料的开发，这些材料有可能改善人类健康，实现更清洁的国内能源经济，提高汽车和飞机部件的重量和耐用性，并扩大电子和太阳能电池的多功能性。这项研究将与教育推广活动相结合，促进科学、技术、工程和数学（STEM）的发展，重点是引导优秀学生——特别是那些来自社会经济贫困背景的学生——进入STEM职业。具体活动将包括扩大pi发起的一项努力，为高中生提供带薪的夏季至秋季研究实习，让本科生参与实验室研究，以及协调硕士学位课程，以巩固本科生向STEM社区的过渡。该职业奖支持聚合物玻璃的理论和计算研究以及教育。强相互作用的聚合物可以表现出极端的特性，有可能实现社会变革的技术，例如在氢键聚合物玻璃中室温保存疫苗，以及由非常不渗透的玻璃聚合物薄膜稳定的柔性太阳能电池和电子产品。决定这些材料性能的动态、机械和输运性质在很大程度上受其玻璃化转变的细节控制，无论是在玻璃化状态下，在玻璃化转变温度下结构冻结“控制”这些性质，还是在玻璃化转变温度以上数百开尔文的更高温度下，玻璃化形成过程可以支配行为。因此，这些材料的合理设计需要对强相互作用聚合物中玻璃形成的预测性理解。然而，理解玻璃化转变足以指导材料设计仍然是材料科学的一大挑战。虽然分子动力学模拟为研究这一现象提供了一个有价值的工具，但它们无法对其物理特性产生预测性的理解，因为它们的速度不够快，无法在靠近玻璃化转变的深度过冷状态下进行模拟，也无法跨越建立全面结构/性质关系所必需的大系统集进行模拟。在强相互作用的聚合物中，这个问题尤其严重，在这种情况下，模拟速度要慢得多，仅基于范德华相互作用的标准理论方法也失效了。本研究项目旨在克服这些挑战并实现两个战略目标：1)确定强相互作用聚合物中与玻璃形成相关的静态和动态特性之间的普遍机制相互关系，包括α弛豫时间、玻璃化转变温度、玻璃形成的脆弱性、玻璃模量、构型熵和自由体积。2)建立基于机理的结构-性能关系，预测这些性能对强相互作用聚合物分子结构的依赖。这些目标将通过采用PI小组开发的一种新的高效的分子动力学模拟玻璃化转变协议来实现，该协议可以在强相互作用的聚合物中进行深度过冷状态和跨大分子性质矩阵的模拟。这些模拟数据将用于建立结构/性质关系，涵盖基于分子水平见解的大范围分子性质。来自这些模拟的数据也将与玻璃形成的理论模型相结合，以建立对强相互作用聚合物中玻璃形成的新的机制理解和理论描述。最终，通过将理论与高通量模拟相结合，该项目将建立结构/性能关系，从而实现基于理论的强相互作用玻璃形成聚合物的设计。这项研究将与教育外展活动相结合，这将推动STEM管道的发展，重点是引导优秀学生——特别是那些来自社会经济贫困背景的学生——进入STEM职业。具体活动将包括扩大pi发起的一项努力，为高中生提供带薪的夏季至秋季研究实习，让本科生参与实验室研究，以及协调硕士学位课程，以巩固本科生向STEM社区的过渡。

NONTECHNICAL SUMMARYThis CAREER award supports theoretical and computational research, and education on soft materials. Transformational technologies ranging from vaccines that remain viable at room temperature to flexible and stable solar cells and electronics await the development of new polymeric materials, soft materials made from long molecular chains with repeating molecular units, that push the limits of material performance. Many of the most promising materials for these new technologies derive their potential from two shared features: they solidify without forming a crystal, through a process known as the glass transition; and their molecules possess strong interactions. At the same time that these features are key to the potential of these materials, they also present a challenge to rational materials design. A fundamental understanding of the physics of the glass transition, the central determinant of the properties of these materials, is still lacking. This problem is especially acute in strongly interacting polymers, because strong interactions are resistant to standard theoretical approaches and are difficult to efficiently capture in computer simulations. As a result, it has not been possible to study molecular behavior at sufficiently long time scales and in sufficiently diverse chemistries to both unravel the fundamental physics of these materials and guide their design.This project is aimed to overcome these challenges. The PI will combine new theoretical approaches and an improved strategy for simulating glass-forming materials to establish fundamental insights and design guidelines for strongly interacting glass-forming polymers. This strategy will enable access to very long time scales and tens of thousands of chemistries to identify common aspects of the molecular physics of these materials and translate them into predictive theories for their properties. This theoretical understanding, in turn, will guide selection of molecular structures yielding unique, targeted material properties. Success of this project will contribute to accelerating the development of materials with the potential to improve human health, enable a cleaner domestic energy economy, enhance the lightness and durability of auto and aircraft components, and broaden the versatility of electronics and solar cells.This research will be integrated with educational outreach activities that will advance a Science, Technology, Engineering, and Mathematics (STEM) pipeline focused on guiding outstanding students - especially those from socioeconomically underprivileged backgrounds - into STEM careers. Specific activities will include expanding a PI-initiated effort offering paid summer-to-fall research internships to high school students, engaging of undergraduates in laboratory research, and coordinating master's degree programs to cement the transition of undergraduate students into the STEM community. TECHNICAL SUMMARYThis CAREER award supports theoretical and computational research, and education on polymer glasses. Strongly interacting polymers can exhibit extreme properties with the potential to enable societally transformational technologies, such as room-temperature preservation of vaccines in hydrogen-bonding polymer glasses and flexible solar cells and electronics stabilized by extraordinarily impermeable glassy polymer films. The dynamic, mechanical, and transport properties that determine the performance of these materials are largely controlled by the details of their glass transition, both in the glassy state where the structure frozen in at the glass transition temperature "controls" these properties and at higher temperatures where the glass formation process can dominate behavior to hundreds of Kelvin above the glass transition temperature. Rational design of these materials therefore demands a predictive understanding of glass formation in strongly interacting polymers. However, an understanding of the glass transition sufficient to guide materials design remains a grand challenge of materials science. While molecular dynamics simulations have provided a valuable tool in the study of this phenomenon, they have been unable to yield a predictive understanding of its physics because their insufficient speed prohibits simulation in the deeply supercooled regime near the glass transition and prevents simulations from spanning the large sets of systems necessary to establish comprehensive structure/property relations. This problem is especially acute in strongly interacting polymers, in which simulations are substantially slower and standard theoretical approaches based only on van der Waals interactions break down. This research project is aimed to overcome these challenges and to accomplish two strategic goals:1) Identify universal mechanistic interrelations between static and dynamic properties associated with glass formation in strongly interacting polymers, including alpha relaxation time, glass transition temperature, fragility of glass formation, glassy modulus, configurational entropy, and free volume. 2) Establish mechanism-based structure-property relations predicting the dependence of these properties on the molecular structure of strongly interacting polymers.These goals will be achieved by employing a novel efficient protocol for molecular dynamics simulation of the glass transition, developed in the PI's group, to perform simulations that access the deeply supercooled regime and span large matrices of molecular properties in strongly interacting polymers. These simulation data will be employed to establish structure/property relations covering a large range of molecular properties based on molecular-level insights. Data from these simulations will also be combined with theoretical models of glass formation to establish new mechanistic understanding and theoretical descriptions of glass formation in strongly interacting polymers. Ultimately, by combining theory with high-throughput simulations, this project will establish structure/property relations to enable theory-based design of strongly-interacting glass-forming polymers. This research will be integrated with educational outreach activities that will advance a STEM pipeline focused on guiding outstanding students - especially those from socioeconomically underprivileged backgrounds - into STEM careers. Specific activities will include expanding a PI-initiated effort offering paid summer-to-fall research internships to high school students, engaging of undergraduates in laboratory research, and coordinating master's degree programs to cement the transition of undergraduate students into the STEM community.