Theory and Modeling of Polymer Crystallization

该奖项支持理论聚合物物理学的综合研究，教育和推广活动。这项研究活动的目的是发展一个新的理论聚合物结晶，采用多种模拟技术和统计力学。聚合物溶液和熔体结晶是高分子科学中一个长期存在的研究问题，充满了神秘感，需要统一的概念主题。对聚合物链如何组织成分级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，并发现了新的规律聚合物组装。这一理论工作补充了世界各地许多实验室正在积极进行的许多实验研究。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。新的理论被用来理解几个技术上重要的问题，其中包括在生长前沿的动力学，自发选择的片层厚度和形状，流动效应，和动力学的melting.Regarding在生长前沿的动力学，目前的分类lamphalin的解决方案和熔体分为两组，表现出不同的温度依赖性的增长速度。 在这里，一个模型，它取决于聚合物的浓度和分子量的开发，统一这两个分类的增长率。 具体的重点是在应用这个新的模型，以确定在更高的浓度和更长的链，迄今为止已经成为可能的增长前沿的分子细节。在参考自发选择的层状厚度和形状，扩展的计算，评估在某些实验有趣的情况下的理论的有效性正在进行中。这些包括多链系统，明确占链刚度，最近邻相互作用，并列入横向和折叠表面能。这使得探索的稳定性的任何介晶的中间state.To解决流动的影响，所谓的shish-kebab配置，确定从以前的研究本研究员，被用作输入动力学蒙特-卡罗模拟。从shish和成核的kebabs开始，已经折叠的链从溶液到shish的附着被模拟，充分考虑了数十万个链。此外，为了解决薄片熔化的动力学，使用基于Langevin的动力学模拟。特别是研究了分子链在薄层边缘离开晶体的演化和机制。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。非技术概述：该奖项支持理论聚合物物理学的综合研究、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，并且在材料科学和生物学中的许多技术相关现象中具有核心重要性。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？在这一领域，世界各地也在进行广泛的实验，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是不同的两类聚合物的生长速率作为温度的函数。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.