Theory of polymer crystallization, melting, and interlude of metastability

非技术总结该奖项支持理论和计算研究，以及促进对聚合物结晶的理解的教育。长而细的链状巨型大分子构成了一类被称为聚合物的材料。这些材料通过服装、建筑材料、汽车和飞机零部件等重新定义了我们当代的文明。聚合材料需要的关键特征之一是能够从它们制造晶体，这样它们才能作为具有市场价值的最终产品使用。但这一大分子过程肯定是一项不可能完成的任务，考虑到大量缠绕在一起的长而交织的电线，可以很容易地想象到这一点。它们如何才能整齐地组织成晶体？事实上，这些分子确实形成了晶体，至少是部分形成。尽管这种偏序聚合物晶体在价值数十亿美元的聚合物行业中很普遍，但人们对这一过程并不了解。从分子上理解聚合物材料的结晶过程是材料界长期面临的研究挑战之一。几十年来在这一领域以现象学的方式收集的大量谜题需要一个合理的概念基础，这将有助于在理解已知事实的同时发现新材料。这项研究计划旨在利用理论和计算机模拟来开发基本概念，以了解聚合物是如何结晶和熔化的。除了推进聚合物结晶领域，拟议的活动还包括大力支持多样性和培养新一代研究生，使他们能够在未来参与价值数十亿美元的半结晶聚合物行业。技术总结该奖项支持理论和计算研究，以及促进对聚合物结晶的理解的教育。聚合物从溶液和熔体中结晶是聚合物科学中一个历史悠久的研究领域，具有巨大的工业价值。由于大量的构象可以被柔性的大分子吸收，它们的结晶和熔化行为表现出广泛的令人费解的现象学，这一直是一个具有挑战性的理解。这些谜题来自多个长度尺度和时间尺度的丰富结构层次，通常涉及长寿的非平衡状态。这项研究计划旨在发展关于聚合物结晶、熔融和介稳状态等级间歇的新理论。基于对长寿命亚稳态和记忆效应在半晶聚合物中的作用的新见解，拟议的研究将使用统计力学、场论和几种模拟技术进行。具体地说，PI计划解决：(I)亚稳状态在结晶、熔化和记忆中的间歇，(Ii)通过片层堆积进行的垂直结晶，(Iii)手性的自发选择和放大，以及(Iv)片层间非晶区的不稳定性。该研究项目的结果预计将对聚合物加工等众多工业相关领域产生重大影响。今天的大多数材料都是由加工过的半晶聚合物制成的，这构成了拟议工作的重点。这些材料构成了一个价值数十亿美元的产业。对这类重要材料的基本了解将有助于设计和加工新型聚合物材料，从而为我们的社会带来更多好处。在这一具有挑战性的研究领域对研究生和博士后研究人员的培训是研究计划的一个强有力的教育组成部分。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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 to advance understanding of polymer crystallization. Very long and thin chain-like gigantic macromolecules make up the class of materials, called polymers. These materials have redefined our contemporary civilization, through clothing, building materials, automobile, and aircraft parts, and much more. One of the key features required in polymeric materials so that they will be useful as end-products with market value, is the ability to make crystals from them. But this macromolecular process must be an impossible task as can be easily envisaged by considering a large number of long and intermingled wires which are all tangled up. How can they organize neatly into crystals? In fact, the molecules do indeed form crystals, at least partially. In spite of the prevalence of such partially ordered polymeric crystals in the multi-billion-dollar industry of polymers, this process is not understood. A molecular understanding of the crystallization process of polymeric materials is one of the longstanding research challenges in the world of materials. The multitude of puzzles collected phenomenologically over many decades in this field demands a rational conceptual foundation, which will facilitate discoveries of new materials in addition to understanding the known facts. This research program is aimed to develop fundamental concepts to understand how polymers crystallize and melt, using theory and computer modelling. In addition to advancing the field of polymer crystallization, the proposed activities include strong support of diversity and training a new generation of graduate students enabling their future participation in the multi-billion-dollar industry of semicrystalline polymers.TECHNICAL SUMMARYThis award supports theoretical and computational research, and education to advance understanding of polymer crystallization. Crystallization of polymers from solutions and melts is one of the longstanding research areas in polymer science with tremendous industrial value. Due to enormous number of conformations that can be taken up by flexible macromolecules, their crystallization and melting behaviors exhibit a broad range of puzzling phenomenology which has been challenging to understand. These puzzles emerge from rich structural hierarchies at multiple length scales and time scales often involving long-lived non-equilibrium states. This research program is aimed to develop new theories of polymer crystallization, melting, and the interlude of hierarchy of metastable states. Building on new insights into the role of long-lived metastable states and memory effects in semicrystalline polymers, the proposed research will be performed using statistical mechanics, field theory, and several simulation techniques. Specifically, the PI plans to address: (i) interlude of metastable states in crystallization, melting, and memory, (ii) vertical crystallization by lamellar stacking, (iii) spontaneous selection and amplification of chirality, and (iv) instability of interlamellar amorphous regions. The results from the research program are expected to have significant impact in numerous industrially relevant areas such as polymer processing. Most of the materials today are made from processed semicrystalline polymers, which form the focus of the proposed work. These materials constitute a multi-billion-dollar industry. A fundamental understanding of this important class of materials will help to design and process novel polymeric materials with enhanced benefits to our society. Training of graduate students and postdoctoral researchers in this challenging research area is a strong educational component of the research program.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.