Theory and Modeling of Polymer Crystallization

聚合物结晶理论和建模

• 批准号: 0706454
• 负责人: Murugappan Muthukumar
• 金额: $ 25.5万
• 依托单位: University of Massachusetts Amherst
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-12-15 至 2010-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0706454&HistoricalAwards=false
• 关键词: Theory; Modeling; Polymer; Crystallization

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.

技术摘要：该奖项支持理论聚合物物理领域的综合研究、教育和推广活动。这项研究活动的目的是通过采用多种模拟技术和统计力学来开发聚合物结晶的新理论。聚合物从溶液和熔体中的结晶是聚合物科学中长期存在的研究问题之一，充满了好奇心并且需要统一的概念主题。对聚合物链如何组织成分层结构的基本理解仍然难以捉摸。这项工作建立了新的概念模型并发现了聚合物组装的新规律。这项理论工作补充了世界各地许多实验室正在积极开展的许多实验研究。研究结果还与许多应用领域相关，例如聚合物加工、聚合物纳米材料的制造和生物自组装。新理论被用来理解几个重要的技术问题，包括生长前沿的动力学、层状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，当前层状的分类溶液和熔体分为两组，它们在生长速率方面表现出不同的温度依赖性。 在这里，开发了一个取决于聚合物浓度和分子量的模型，该模型统一了这两种类别的增长率。 具体重点是应用这个新模型来确定更高浓度和更长链的生长前沿的分子细节，这在以前是可能的。关于层状厚度和形状的自发选择，评估计算有效性的扩展该理论在某些有趣的实验情况下正在进行中。其中包括多链系统，明确考虑链刚度、最近邻相互作用以及包含横向和折叠表面能。这使得能够探索任何介晶中间态的稳定性。为了解决流动效应，从本研究人员之前的研究中确定的所谓的 shish-kebab 配置被用作动力学蒙特卡罗模拟的输入。从羊肉串和有核烤肉串开始，模拟了溶液中已经折叠的链在羊肉串上的附着，充分考虑了数十万条链。此外，为了解决薄片熔化的动力学问题，基于 Langevin 的动力学模拟被使用。特别是研究了允许片层外围的链离开晶体的演化和机制。除了研究之外，该研究还包括本科生、研究生和博士后科学家的教育。非技术摘要：该奖项支持集成理论聚合物物理领域的研究、教育和推广活动。该研究旨在了解聚合物（由许多较小的重复分子单元组成的大型长链分子）如何组织成有序状态，这对于材料科学和生物学中的许多技术相关现象至关重要。受聚合物影响的技术包括橡胶、塑料和纤维。 该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相关的理论问题，即：聚合物如何结晶？世界范围内也在这一领域开展了广泛的实验工作，并出现了许多具有挑战性的难题。正在开发一种基于聚合物浓度和重量的模型，该模型可以确定目前被认为不同的两类聚合物的生长速率作为温度的函数。除了研究之外，研究还包括本科生、研究生和博士后科学家的教育。