CAREER: Evaluating Theories of Polymer Crystallization by Directly Calculating the Nucleation Barrier in a Polymer Melt

职业：通过直接计算聚合物熔体中的成核势垒来评估聚合物结晶理论

• 批准号: 2338690
• 负责人: Douglas Tree
• 金额: $ 50.88万
• 依托单位: Brigham Young University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2024
• 资助国家: 美国
• 起止时间: 2024-03-01 至 2029-02-28
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2338690&HistoricalAwards=false
• 关键词: CAREER; Evaluating; Theories; Polymer; Crystallization

NONTECHNICAL SUMMARYPolymers are long-chain molecules found in a wide array of natural and man-made materials, ranging from DNA, wood, and rubber to piping, clothing, and grocery bags. Many essential polymer materials have a structure that is at least partially crystalline, meaning the atoms within the molecule arrange themselves regularly in space. Crystallinity plays a crucial role in determining the properties of polymer materials, and thus it is critical that scientists and engineers be able to understand and manipulate how and when polymers crystallize.Despite extensive research, the exact mechanism behind polymers crystallization remains unknown. There are several competing theories, but evidence from experiments and computer simulations has been inconclusive. This project will apply a simulation method that was successfully used to study the crystallization of non-polymers such as water to study polymers. The project objectives will focus on studying how the length of the molecules and the different types of polymers affect the mechanism of crystallization. Success with this new approach could revolutionize our basic understanding of how polymers form crystals, potentially leading to the development of innovative new materials and reduced environmental impacts from existing ones.The project will also include educational objectives that are integrated with research activities. Specifically, the project will create mentoring opportunities between undergraduates and K-12 students, between the PI and undergraduates, between more and less experienced graduate students, and between the PI and future scientists through the creation of a podcast that focuses on career development in the sciences.TECHNICAL SUMMARYDespite decades of research, polymer science lacks a widely accepted theory for crystallization from the melt state. The development of an accurate theory of polymer crystallization would not only change textbooks, but it would also enable the creation of new polymers with better properties and processes for making polymers with less environmental impact.Nucleation processes are foundational to polymer crystallization, but accumulating evidence suggests that Classical Nucleation Theory inadequately explains homogeneous nucleation, leading researchers to propose controversial alternative theories. The central hypothesis of this project is that equilibrium advanced sampling methods can be used to directly calculate the nucleation barrier to test these new theories. While new to polymer crystallization, advanced sampling methods have been used study nucleation in other fields, and they have distinct advantages over other methods. Accordingly, this project will focus on a study of the nucleation barrier for folded-chain crystals as a function of polymer molecular weight and as a function of polymer chemistry. This project will also contribute to the ongoing development of simulation software for computing free energy landscapes in low-temperature polymer melts.The project will also involve integrated research and teaching aims specifically focusing on effective and scalable mentoring opportunities for students spanning from K-12 through graduate education levels. Mentoring new scientists and engineers, especially underrepresented minorities, is a key educational component of cultivating a globally competitive and diverse workforce. Specific mentoring activities include near-peer mentoring and outreach to K-12 students, PI-mentored undergraduate research, scalable mentoring experiences through the production and distribution of the podcast ``How Science Happens,'' and near-peer mentoring of graduate students through a chemical engineering student council.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.

非技术概要聚合物是长链分子，广泛存在于各种天然和人造材料中，从 DNA、木材和橡胶到管道、衣服和杂货袋。许多重要的聚合物材料具有至少部分结晶的结构，这意味着分子内的原子在空间中规则地排列。结晶度在决定聚合物材料的性能方面起着至关重要的作用，因此科学家和工程师能够理解和操纵聚合物结晶的方式和时间至关重要。尽管进行了大量研究，但聚合物结晶背后的确切机制仍然未知。有几种相互竞争的理论，但实验和计算机模拟的证据尚无定论。该项目将应用一种成功用于研究水等非聚合物结晶的模拟方法来研究聚合物。该项目的目标将重点研究分子长度和不同类型的聚合物如何影响结晶机制。这种新方法的成功可能会彻底改变我们对聚合物如何形成晶体的基本理解，有可能导致创新新材料的开发并减少现有材料对环境的影响。该项目还将包括与研究活动相结合的教育目标。具体来说，该项目将通过创建一个专注于职业发展的播客，在本科生和 K-12 学生之间、在 PI 和本科生之间、在经验丰富和经验不足的研究生之间、以及在 PI 和未来科学家之间创造指导机会。技术摘要尽管经过数十年的研究，聚合物科学仍缺乏广泛接受的熔融态结晶理论。准确的聚合物结晶理论的发展不仅会改变教科书，而且还能够创造出具有更好性能的新聚合物以及对环境影响较小的聚合物制造工艺。成核过程是聚合物结晶的基础，但越来越多的证据表明经典成核理论不足以解释均质成核，导致研究人员提出有争议的替代理论。该项目的中心假设是可以使用平衡高级采样方法直接计算成核势垒来检验这些新理论。虽然先进的采样方法对于聚合物结晶来说是新事物，但已用于其他领域的成核研究，并且与其他方法相比具有明显的优势。因此，该项目将重点研究折叠链晶体的成核势垒作为聚合物分子量和聚合物化学的函数。该项目还将有助于持续开发用于计算低温聚合物熔体中自由能景观的模拟软件。该项目还将涉及综合研究和教学目标，特别注重为从 K-12 到学生提供有效和可扩展的指导机会研究生教育水平。指导新科学家和工程师，特别是代表性不足的少数族裔，是培养具有全球竞争力和多元化劳动力的关键教育组成部分。具体的指导活动包括对 K-12 学生的近同侪指导和外展、PI 指导的本科生研究、通过制作和分发播客“科学如何发生”来提供可扩展的指导经验，以及通过以下方式对研究生进行近同侪指导：该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。