Multiscale Theory For Semicrystalline Polymers

半晶聚合物的多尺度理论

• 批准号: 0907370
• 负责人: Scott Milner
• 金额: $ 27万
• 依托单位: Pennsylvania State Univ University Park
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-09-15 至 2013-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0907370&HistoricalAwards=false
• 关键词: Multiscale; Theory; Semicrystalline; Polymers

TECHNICAL SUMMARYThis award supports theoretical research and education on polymer crystallization. The long-chain nature of polymer molecules dictates that polymeric crystals adopt a chain-folded lamellar form, but the basic question of how the crystals nucleate is ill understood. There is experimental evidence that polyethylene, the most common semicrystalline polymer, actually nucleates via an intermediate ?rotator" mesophase. However, no theoretical basis yet exists to assess this intriguing hypothesis, or to ascertain how widespread this phenomenon might be in other polymers. Progress requires a theory of the mesophases, able to compute not only their free energy relative to the melt and crystal phases, but also the free energy of the interface between the melt and the mesophase or crystal.An effective theory of the crystal-melt interface in semicrystalline polymers would also predict the concentration of ?tie chains", which link together adjacent crystalline lamellae and lead to the toughness and ductility of plastics. Also, there is much current interest in the effect of flow on crystallization kinetics and morphology. This is crucial in commercial use of semicrystalline polymers, which are very sensitive to flow effects. Without a good theory of quiescent crystallization, any effort to understand how flow speeds up nucleation is severely handicapped.The PI aims to develop the theoretical basis to understand the mesophases in polyethylene. It will lead to predictions for bulk and surface free energies, and it will determine whether nucleation in polyethylene can indeed occur via a mesophase. Given the inherently multiscale nature of the problem, a transformative synthesis of techniques will be employed: atomistic simulation of ordered phases, novel use of ?solid-state simulations" to characterize mesophase domain walls, mesoscopic discrete-spin simulation of partially ordered mesophases, and a new adaptation of grafted chain ?brush" theory of the interface between ordered polymer phases and adjacent melt. This unique combination of strategies will lead to a better understanding of how polymer crystals nucleate, and will bring us closer to achieving optimal properties of these truly modern materials.This intellectually rich problem of practical importance provides an excellent opportunity for education, offering students and postdocs broad exposure to theory, analytical methods, atomistic and mesoscale simulation. The PI is developing an undergraduate course for Fall 2009 in Polymers and Complex Fluids, which is well aligned with the multiscale approach of this proposal. The Chemical Engineering Department has a strong record of minority and gender representation among its graduate students, with about 30 percent women. The College of Engineering has an active Women In Engineering Program and a Multicultural Engineering Program. All simulations will be performed with open source software, to remove any barrier to use by others. NON-TECHNICAL SUMMARYThis award supports theoretical and computational research and education on how polymers crystallize. Semicrystalline polymers, although relatively young, are the most ubiquitous materials of the modern age. The mass of such materials now produced worldwide each year exceeds the production of steel. Even so, their ultimate potential for desirable mechanical and physical properties is as yet unfulfilled. This is because, in contrast to the centuries-old field of metallurgy, the science base for semicrystalline polymers is still very much a work in progress, with many key results obtained only in the past few decades. Likewise, improved control of polymer molecular structure through advances in catalysis has emerged only relatively recently.The PI will use theoretical techniques to explore a possible microscopic mechanism for crystallization through an intermediate polymer phase. This intellectually rich problem of practical importance provides an excellent opportunity for education, offering students and postdocs broad exposure to theory, analytical methods, atomistic and mesoscale simulation. The PI is developing an undergraduate course for Fall 2009 in Polymers and Complex Fluids, which is well aligned with the multiscale approach of this proposal. The Chemical Engineering Department has a strong record of minority and gender representation among its graduate students, with about 30 percent women. The College of Engineering has an active Women In Engineering Program and a Multicultural Engineering Program. All simulations will be performed with open source software, to remove any barrier to use by others.

该奖项支持聚合物结晶的理论研究和教育。聚合物分子的长链性质决定了聚合物晶体采用链折叠的层状形式，但晶体如何成核的基本问题还不清楚。有实验证据表明，聚乙烯，最常见的半结晶聚合物，实际上是通过一个中间体成核？转子”中间相。然而，还没有理论基础来评估这个有趣的假设，或者确定这种现象在其他聚合物中的普遍程度。发展需要一个中间相的理论，不仅能够计算它们相对于熔体和晶体相的自由能，而且能够计算熔体和中间相或晶体之间界面的自由能。“系链”，将相邻的结晶层连接在一起，导致塑料的韧性和延展性。此外，有很多当前的兴趣在流动的结晶动力学和形态的影响。这在半结晶聚合物的商业应用中是至关重要的，半结晶聚合物对流动效应非常敏感。没有一个好的静态结晶理论，任何努力，以了解如何流动加速成核是严重hantem.The PI的目的是发展的理论基础，了解聚乙烯中的中间相。它将导致预测的体积和表面自由能，它将确定是否在聚乙烯成核确实可以通过中间相发生。鉴于固有的多尺度性质的问题，一个变革性的综合技术将采用：原子模拟有序相，新的使用？固态模拟”来表征中间相畴壁，介观离散自旋模拟部分有序的中间相，和一个新的适应接枝链？有序聚合物相和相邻熔体之间界面的“刷”理论。这种独特的策略组合将导致更好地了解聚合物晶体如何成核，并将使我们更接近实现这些真正现代材料的最佳性能。这个智力丰富的实际重要性问题提供了一个极好的教育机会，为学生和博士后提供广泛接触理论，分析方法，原子和介观模拟。PI正在为2009年秋季的聚合物和复杂流体开发一门本科课程，这与本提案的多尺度方法非常一致。化学工程系在其研究生中少数民族和性别代表性方面有着良好的记录，约有30%的女性。工程学院有一个活跃的妇女在工程方案和多元文化工程方案。所有模拟都将使用开源软件进行，以消除其他人使用的任何障碍。非技术总结该奖项支持聚合物结晶方式的理论和计算研究和教育。半结晶聚合物，虽然相对年轻，是现代最普遍的材料。现在，全世界每年生产的这种材料的质量超过了钢的产量。即便如此，它们在理想的机械和物理性能方面的最终潜力尚未得到满足。这是因为，与有着数百年历史的冶金学领域相比，半结晶聚合物的科学基础仍然是一项正在进行的工作，许多关键成果只是在过去几十年中才获得的。同样，通过催化剂的进步来改善聚合物分子结构的控制也是最近才出现的。PI将使用理论技术来探索通过中间聚合物相结晶的可能微观机制。这个智力丰富的实际重要性的问题提供了一个很好的教育机会，为学生和博士后广泛接触理论，分析方法，原子和中尺度模拟。PI正在为2009年秋季的聚合物和复杂流体开发一门本科课程，这与本提案的多尺度方法非常一致。化学工程系在其研究生中少数民族和性别代表性方面有着良好的记录，约有30%的女性。工程学院有一个活跃的妇女在工程方案和多元文化工程方案。所有模拟都将使用开源软件进行，以消除其他人使用的任何障碍。