Flow induced crystallisation in polymers: from molecules to processing

聚合物加工是一项价值数十亿英镑的全球性产业，其生产的产品几乎每天都被发达国家（及其他国家）的每个人使用。这一英国经济的重要部门将从对聚合物在加工过程中如何结晶的分子理解中获得显著的竞争优势，因为它将使塑料产品更坚固、更轻、更耐用、更容易回收。在本提案中，我们将克服理解聚合物结晶的关键实验，模拟和数值问题，为半结晶聚合物的加工提供基于分子的预测平台。我们将紧密集成一系列逐渐粗粒度的模拟和模型，涵盖单个项目内所有相关的长度尺度。这将取代目前在聚合物加工中的次优半经验方法，并通过选择加工条件实现聚合物产品的分子设计。通过促进具有定制特性的聚合物产品的制造，该项目将为这一重要行业提供关键的竞争优势。聚合物是由大量简单分子连接而成的长链分子。这些长链分子是价值数十亿英镑的塑料工业的核心。半结晶聚合物占世界合成聚合物产量的很大一部分。与简单分子不同，聚合物分子的连通性意味着它们会结晶成结晶和非晶态区域的复合结构。非晶材料和结晶材料的比例，以及晶体的排列和取向，统称为形态。晶体形态强烈地影响强度、韧性、渗透性、表面纹理、透明度、回收能力和几乎任何其他实际感兴趣的性能。此外，聚合物结晶从根本上受到聚合物加工中无处不在的流动的影响。流动极大地提高了聚合物结晶的速度，并对其形态产生了深远的影响。流动扭曲了聚合物链的构型，这种扭曲打破了结晶的动力学障碍，并指导了最终的形态。了解聚合物的结晶是一个棘手的问题。相关的长度尺度范围很大，从单体（纳米）的大小到接近宏观的晶体（微米）。时间尺度的范围更广，从单体弛豫时间（ns）到成核时间（低过冷时的小时数）。我们的项目将涉及广泛的多尺度建模，并在每个层面上通过专门设计的实验来解决关键的建模问题。我们的实验将涉及控制流动几何，分子质量的系统变化和成核和整体结晶的探针。实验和各级建模的紧密结合是一个关键特征。我们将开发一个相互关联的多层次多尺度模型家族，跨越所有相关的长度尺度，并在分段方法无效的地方提供结果。每种技术都将与其邻居紧密结合，在逐步解决日益具有挑战性的系统的同时，保留模型的分子基础。这将随着低过冷度和高分子量的聚合物加工特性而累积。每次模拟都将使用罕见事件算法来显著提高成核率，这是非常长的时间尺度的原因。从最详细的模型中获得的洞察力将指导更快建模的发展。在最高的粗粒度下，该程序将推导出适合于聚合物加工计算建模的模型。在尖端的有限元代码中使用这些模型，我们将计算聚合物加工几何中的FIC行为。

Polymer processing is a multi-billion pound, world-wide industry, manufacturing products used by virtually every person in the developed world (and beyond) on a daily basis. This vital sector of the UK economy will gain a significant competitive advantage from a molecular understanding of how polymers crystallise during processing, as it will enable stronger, lighter, more durable and more easily recycled plastic products. In this proposal we will overcome the key experimental, simulation and numerical issues in understanding polymer crystallisation to deliver a molecular based, predictive platform for the processing of semi-crystalline polymers. We will tightly integrate a family of progressively coarse-grained simulations and models, covering all relevant lengthscales within a single project. This will displace the current sub-optimal semi-empirical approaches in polymer processing and enable molecular design of polymer products, through choice of processing conditions. By facilitating the manufacture of polymer products with tailored properties this program will provide a critical competitive advantage to this important industry.Polymers are long-chain molecules, formed from connecting together a large number of simple molecules. These long-chain molecules are at the heart of the multi-billion pound plastics industry. Semi-crystalline polymers make up a very significant fraction of the worlds production of synthetic polymers. Unlike simple molecules, the connectivity of polymer molecules means they crystallise into a composite structure of crystalline and amorphous regions. The proportion of amorphous and crystalline material, along with the arrangement and orientation of the crystals, is collectively known as the morphology. The crystal morphology strongly influences strength, toughness, permeability, surface texture, transparency, capacity to be recycled and almost any other property of practical interest. Furthermore, polymer crystallisation is radically influenced by the flows that are ubiquitous in polymer processing. Flow drastically enhances the rate at which polymers crystallise and has a profound effect on their morphology. Flow distorts the configuration of polymer chains and this distortion breaks down the kinetic barriers to crystallisation and directs the resulting morphology.Understanding polymer crystallisation is a formidable problem. The huge range of relevant lengthscales ranges from the size of a monomer (nm) up to near macroscopic crystals (micro-metres). The range of timescales is even wider, ranging from the monomer relaxation time (ns) to nucleation (hours at low under-cooling). Our project will involve extensive multiscale modelling, supported at each level by experiments specifically designed to address key modelling issues. Our experiments will involve controlled flow geometries, the systematic variation of molecular weight and the probes of both nucleation and overall crystallisation. Close integration of experiments and all levels of modelling is a key feature.We will develop an interrelated hierarchical family of multiscale models, spanning all relevant lengthscales and delivering results where piecewise approaches have been ineffective. Each technique will be tightly integrated with its neighbours, retaining the molecular basis of the models while progressively addressing increasingly challenging systems. This will cumulate with the low-undercooling and high-molecular weights that are characteristic of polymer processing. Each simulation will use a rare event algorithm to dramatically increase the nucleation rate, the cause of the very long timescales. Insight from the most detailed models will guide the development of faster modelling. At the highest coarse-graining, the program will derive models suitable for computational modelling of polymer processing. Using these models in cutting-edge finite element code, we will compute FIC behaviour in polymer processing geometries.