Materials World Network: Spatio-Temporal Development of Structure during Flow-Induced Crystallization of Polyolefins

这个由加州理工学院（Caltech）和荷兰因托芬工业大学（TU/e）合作的综合项目旨在建立流动引起的聚合物结晶动力学和形态变化的预测模型。聚合物是正在进行的材料革命中必不可少的参与者。半晶聚合物占所有合成聚合物年产量的三分之二以上，并且正处于复兴之中，因为最近开发的茂金属催化剂可以通过更精细的分子结构控制来实现最终性能的新组合。不幸的是，新的合成能力需要许多年才能交付新产品：由于对结构-加工-性能的关系仍然知之甚少，因此需要进行大量的试验和错误。加工改变了结晶的速率、形态和各向异性，可以使结晶速度加快几个数量级，并对材料的机械强度和透气性等性能产生深远的影响。这个合作项目将提供原理和计算模型，使大分子的设计能够考虑到处理动力学。加州理工学院的研究揭示了流动诱导结晶的早期事件及其在熔体动力学中的起源。流动可以打开成核的动力学途径，使成核的速率跟踪熔体中分子运动的速率。在流动模板过程中形成的定向前体，随后定向生长；前驱体之间的距离决定了定向结构完成的时间。为了将这些新的实验发现转化为可以付诸实践的设计工具，需要在理论和建模方面取得相应的进展。因此，这个合作项目将加州理工学院的实验能力与被广泛认为是世界领先的聚合物加工建模团队——由Han Meijer领导的埃因霍温团队——联系在一起。它们在加工过程中模拟结构发展的强大能力将被扩展到将聚合物的分子规格与描述结晶前体形成及其上晶体生长的动力学参数联系起来。反过来，扩展的模型将预测分子参数的函数趋势，这将在实验中得到验证。综合建模和实验将阐明加工影响聚合物结构发展的基本机制，作为树脂分子特性和施加的流动和热历史的函数。从技术上讲，结合流动诱导结晶分子过程的基本知识的模型可以彻底改变半结晶聚合物的设计和聚合物加工的优化。材料世界网络的奖项使这一连贯的模拟和实验计划成为可能，这将提供新一代设计工具，加速聚烯烃新产品的开发，聚烯烃是热塑性塑料行业最大的一部分，每年消耗超过7000万吨。该奖项由材料研究部和国际科学与工程办公室共同资助

This integrated program between the California Institute of Technology (Caltech) and the Technical University of Einthoven (TU/e) aims to establish predictive models of flow-induced changes in polymer crystallization kinetics and morphology. Polymers are essential players in the ongoing materials revolution. Semicrystalline polymers comprise over two-thirds of the annual production of all synthetic polymers and are in the midst of a renaissance, as recently developed metallocene catalysts allow new combinations of final properties through finer control of the molecular structure. Unfortunately, new synthetic capabilities take many years to deliver new products: extensive trial and error is required because structure-processing-property relations remain poorly understood. Processing alters the rate, form and anisotropy of crystallization: it can accelerate crystallization by orders of magnitude, and it has a profound effect on material properties, such as mechanical strength and gas permeability. This collaborative project will provide principles and computational models that are needed to enable design of macromolecules with processing dynamics in mind.Research at Caltech has revealed early events in flow-induced crystallization and their origin in the dynamics of the melt. Flow can open a kinetic pathway to nucleation, such that the rate of nucleation tracks the rate of molecular motion in the melt.Oriented precursors formed during flow template subsequent oriented growth; the distance between the precursors governs the time for completion of the oriented structure.To translate these new experimental findings into design tools that can be put into practice, corresponding advances in theory and modeling are needed. Therefore, this collaborative program links Caltech's experimental capabilities with what is widely regarded as the world's leading team in modeling polymer processing: the Eindhoven group led by Han Meijer. Their powerful capabilities to model structure development during processing will be extended to connect molecular specifications of the polymer with the kinetic parameters that describe the formation of crystallization precursors and the growth of crystallites on them. In turn, the expanded model will predict trends as a function of molecular parameters, which will be tested experimentally.Integrated modeling and experiment will elucidate the fundamental mechanism by which processing affects polymer structure development as a function of resin molecular characteristics and the imposed flow and thermal history. Technologically, models that incorporate fundamental knowledge of the molecular processes involved in flow-induced crystallization could revolutionize design of semicrystalline polymers and optimization of polymer processing. The Materials World Network award enables this coherent program of simulation and experiment, which will provide a new generation of design tools that will accelerate new product development in polyolefins the largest segment of the thermoplastics industry, consumed at a rate of over 70 million metric tons per year.This award is co-funded by the Division of Materials Research and the Office of International Science and Engineering