Theory and Modeling of Polymer Crystallization

技术概述：该奖项支持理论聚合物物理的综合研究、教育和推广活动。本研究的目的是利用多种模拟技术和统计力学，发展一种新的聚合物结晶理论。聚合物从溶液和熔体中结晶是聚合物科学中长期存在的研究问题之一，充满阴谋，需要统一的概念主题。对聚合物链如何组织成层次化结构的基本理解仍然是难以捉摸的。这项工作建立了新的概念模型，发现了聚合物组装的新规律。这一理论努力是对世界各地许多实验室积极开展的许多实验研究的补充。这些结果也与许多应用领域有关，如聚合物加工、聚合物纳米材料的制造和生物自组装。这一新理论正被用来理解几个重要的技术问题，包括生长前沿的动力学，片层厚度和形状的自发选择，流动效应，以及熔化动力学。关于生长前沿的动力学，目前溶液和熔体中的片层的分类被分为两类，它们在生长速率上表现出不同的温度依赖性。在这里，建立了一个依赖于聚合物浓度和相对分子质量的模型，该模型统一了这两种类型的增长率。具体的焦点是应用这个新的模型来确定生长前沿的分子细节，在更高的浓度和更长的链上是可能的。关于自发选择片层厚度和形状，评估理论在某些实验有趣情况下的有效性的计算的扩展正在进行中。这些系统包括多链系统，明确考虑了链的刚性、最近邻相互作用以及包含侧向和折叠表面的能量。为了解决流动效应的问题，我们使用了这个研究者以前的研究中确定的所谓的shish-kebab构型作为动力学蒙特卡罗模拟的输入。从Shish和成核的烤肉串开始，在充分考虑了数十万个链的情况下，模拟了已经折叠的链从溶液到Shish的附着。此外，为了研究片层的熔化动力学，使用了基于朗之万法的动力学模拟。特别是，研究了使片层外围的链离开晶体的进化和机制。除了研究，本科生、研究生和博士后科学家的教育也包括在研究中。非技术总结：该奖项支持理论聚合物物理的综合研究、教育和推广活动。这项研究试图了解聚合物，即由许多较小的重复分子单元组成的大的长链分子是如何组织成有序状态的，并在材料科学和生物学中的许多技术相关现象中发挥核心作用。受聚合物影响的技术包括橡胶、塑料和纤维。这个项目解决了与聚合物研究前沿的一个非常具有挑战性的问题有关的理论问题，即：聚合物是如何结晶的？世界各地也在这一领域开展广泛的试验工作，出现了许多具有挑战性的谜题。一种基于聚合物浓度和重量的模型正在开发中，该模型可以确定作为温度函数的两类聚合物的生长速度，这两种聚合物目前被认为是不同的。除了研究，本科生、研究生和博士后科学家的教育也包括在研究中。

TECHNICAL SUMMARY:This award supports integrated research, education and outreach activities in theoretical polymer physics. This research activity is aimed of developing a new theory of polymer crystallization, by employing several simulation techniques and statistical mechanics. Crystallization of polymers from solutions and melts is one of the longstanding research problems in polymer science, full of intrigue and in need of unifying conceptual themes. A fundamental understanding of how polymer chains organize into hierarchical structures is still elusive. This work builds new conceptual models and discovers new laws of polymer assembly. This theoretical effort complements many experimental investigations being actively pursued in many laboratories worldwide. The results are also relevant to numerous applied areas such as polymer processing, fabrication of polymeric nanomaterials and biological self-assembly. The new theory is being used to understand several technologically important questions which include kinetics at the growth front, spontaneous selection of lamellar thickness and shape, flow effects, and the kinetics of melting.Regarding the kinetics at the growth front, current classifications of lamellae in solutions and melts are divided into two groups that exhibit different temperature dependencies in the growth rates. Here, a model which depends upon polymer concentration and molecular weight is developed which unifies the growth rates of these two classifications. Specific focus is in applying this new model to determine the molecular details at the growth front at higher concentrations and for longer chains that has heretofore been possible.In reference to spontaneous selection of lamellar thickness and shape, extensions of the calculations which assess the validity of the theory in certain experimentally interesting situations are underway. These include many-chain systems, explicitly accounting for chain stiffness, nearest-neighbor interactions, and inclusion of lateral- and fold- surface energies. This enables the exploration of the stability of any mesomorphic intermediate state.To address flow effects the so-called shish-kebab configurations, identified from previous research of this investigator, are used as input for kinetic Monte-Carlo simulations. Starting from the shish and nucleated kebabs, the attachment of already folded chains from the solution onto the shish is simulated with full account of hundreds of thousands of chains.Also, to address the kinetics of melting of the lamella, Langevin-based dynamical simulations are being used. In particular the evolution and mechanisms which allow chains at the periphery of the lamella to exit the crystal are investigated.In addition to research, education of undergraduate, graduate and postdoctoral scientists is included in the research.NON-TECHNICAL SUMMARY:This award supports integrated research, education and outreach activities in theoretical polymer physics. The research seeks to understand how, polymers, large long-chain molecules made of many smaller repeating molecular units, organize into ordered states and is of central importance in many technologically relevant phenomena in materials science and biology. Technologies impacted by polymers include rubbers, plastics, and fibers. This project addresses theoretical issues related to a very challenging question at the forefront of polymer research, namely: how do polymers crystallize? Extensive experimental efforts are also being mounted worldwide in this area and many challenging puzzles have emerged. A model based upon polymer concentration and weight is being developed which can determine growth rates as a function of temperature for two classes of polymers that are currently thought of as distinct. In addition to research, education of undergraduate, graduate and postdoctoral scientists is included in the research.