CAREER: Novel Coarse-Grained Simulations to Study Relationships Linking Morphology and Plastic Resistance in Semi-Crystalline Polymers

该学院早期职业发展（Career）项目将支持分子尺度上的材料结构如何影响半结晶塑料宏观物理特性的基础研究，并通过创建新的多尺度方法来加速计算模拟。塑料因其优异的性能，包括高强度重量比、耐化学性和耐用性，被广泛用于各种产品中。塑料是由有机聚合物制成的，有机聚合物是由许多重复单元组成的长分子，其结构和化学性质决定了材料的性质。在纳米尺度上，半结晶聚合物由高度有序或无序的长分子链区域的混合物组成。这些不同相的显著不同的机械性能，当结合在一起时，可以产生非常坚韧和坚硬的材料。在过去的几十年里，成本高昂的经验努力主要用于逐步寻找改进的化学和材料加工，以制造更坚固、更坚韧的塑料。需要精确和有效的模拟方法来取代这些经验的努力，这是缩短今天的关键一步。10-20年的材料开发周期。因此，这项研究的结果将促进塑料制造业的新创新，这是美国为数不多的贸易顺差制造业之一，最终使美国经济和社会受益。此外，将教育和推广活动与这项研究工作相结合，将有助于解决国家面临的挑战，以满足未来对丰富、多样化和有才华的工程劳动力的需求。例如，有效的学习将通过适应性和智能的基于网络的教育系统和合作学习来促进，后者还将用于确定重点高中学生讲习班的导师。由于众所周知的可表征性和可转移性问题，粗粒度分子模型在描述聚合物力学的程度上受到限制。此外，它们的使用通常仅限于模拟单相材料，如聚合物熔体或聚合物玻璃。这项研究工作的科学目标是创建并验证一个多尺度计算框架，该框架为生成半结晶聚合物的粗粒度分子模型提供了系统方法，这些模型经过优化，可以保留相关非弹性变形机制的基本运动学细节。研究团队将开发和训练粗粒度模型，并对模型进行验证和验证，以确保在粗粒度转换过程中松弛时间尺度的谱得到保留。该团队还将运用新开发的模型来确定相间结构与机械性能（如防滑性能）之间的关系。

This Faculty Early Career Development (CAREER) program will support fundamental research on how material structure at the molecular scale affects macroscopic physical properties of semi-crystalline plastics, facilitated by the creation of a new multiscale methodology for accelerated computational simulations. Plastics are used in a vast range of products for their excellent properties including high strength to weight ratio, chemical resistance, and durability. Plastics are made of organic polymers, long molecules composed of many repeating units, whose structure and chemistry dictate the material properties. At the nanoscale, semi-crystalline polymers are composed of a mixture of regions in which long molecular chains are either highly ordered or disordered. The significantly different mechanical properties of these different phases can, when combined, lead to remarkably tough and stiff materials. Over the past decades, costly empirical efforts have been predominantly employed to progressively search for improved chemistries and material processing in order to create stronger and tougher plastics. Accurate and efficient simulation methods are needed to replace these empirical efforts, a critical step in shortening today?s 10-20 year materials development cycle. Therefore, results from this research will foster new innovation in plastics manufacturing, one of the few U.S. manufacturing sectors with a trade surplus, ultimately benefiting the U.S. economy and society. Furthermore, the integration of educational and outreach activities with this research effort will help to address national challenges in meeting future demands for an abundant, diverse, and talented engineering workforce. For example, efficient learning will be facilitated through an adaptive and intelligent web-based educational system and cooperative learning, the latter of which will also be used to identify mentors for focused high school student workshops. Coarse-grained molecular models are limited in the extent to which they can describe polymer mechanics due to well-known problems of representability and transferability. Furthermore, their usage has been typically limited to simulations of single phase materials such as polymer melts or polymer glasses. The scientific objective of this research effort is to create and validate a multiscale computational framework that provides a systematic approach for generating coarse-grained molecular models of semi-crystalline polymers, which are optimized so that they preserve the essential kinematic details of relevant inelastic deformation mechanisms. The research team will develop and train coarse-grained models, and conduct verification and validation of the models to ensure that the spectrum of relaxation timescales is preserved across the coarse-grained transformation. The team will also exercise the newly developed models to identify relationships between interphase structure and mechanical properties such as slip resistance.