Understanding the Impact of Confinement on the Dynamics of Entangled Chains

非技术概要：塑料材料（聚合物）的多样性和柔韧性改变了我们的生活。十亿分之一米大小的颗粒（纳米颗粒）的出现可以提供更灵活、更坚固的材料，具有优越的性能，因为数十亿个这样的颗粒可以结合到聚合物中，从而产生纳米复合材料。现代化学可以在分子水平上修饰这些纳米粒子，从而对其材料行为产生重大影响，通常具有未知的新特性。挑战在于发展分子操作和宏观性质之间的关系。该项目通过控制和改变纳米颗粒的空间分布以及修改附着在这些颗粒表面的聚合物分子来完成这项任务。在这些条件下，纳米粒子约束的影响将使用先进的实验技术进行研究。该项目包括了解纳米复合材料的力学性能与纳米颗粒空间分布之间的关系，以及在分子长度尺度上的理论描述。本研究亦与学生教育相结合，让学生接触各种先进的实验技术。技术概述：本研究将研究纳米约束对聚合物熔体的影响。重点将放在纳米颗粒分散、表面和链接枝到表面的影响对链动力学的操纵上。目前的理解受到知识空白的限制，其中包括缺乏对链动力学的理论理解，以及如何区分颗粒分散和聚合物链的影响。一个整体的方法，包括小角度x射线散射（SAXS），介电光谱（DS）和流变性，将被用来发展一个理论，基于最近的进展，同时描述聚合物熔体的介电性质和流变性。将研究分散在聚合物基质中的纳米颗粒链的复合材料。通过接枝密度、自由链分子量和相应的NTPs特性可以控制NTPs的分散。SAXS的静态结构因子可用于获得凝聚和非凝聚粒子体系的相图，并提供有关约束长度尺度的信息。将探讨纳米颗粒施加的额外约束对链动力学的影响，以及表面引起的聚合物管径的变化。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL SUMMARY:The variety and flexible properties of plastic materials (polymers) has changed our lives. The emergence of particles with a size as tiny as a billionth of a meter (nanoparticles) can provide even more flexible and stronger materials with superior properties as billions of these particles can be incorporated into polymers to yield nanocomposite materials. Modern chemistry can modify these nanoparticles at the molecular level, which leads to a substantial impact on their material behavior, often with unknown and novel properties. The challenge is to develop a relationship between molecular manipulations and macroscopic properties. This project approaches this task by controlling and varying the spatial distribution of the nanoparticles and by modifying the polymer molecules attached to the surfaces of these particles. The effects of nanoparticle confinement under these conditions will then be studied using advanced experimental techniques. The project includes the understanding of the relationship between mechanical properties of the nanocomposite materials and the spatial distribution of the nanoparticles, as well as the theoretical description at the molecular length-scale. This research is also integrated with education of students and exposing them to a variety of advanced experimental techniques.TECHNICAL SUMMARY:The effects imposed by nanoconfinement on polymer melts will be studied in this research. Emphasis will be on the manipulation of the chain dynamics by nanoparticle dispersion, surfaces, and the influence of chains grafted to surfaces. The current understanding is limited by knowledge gaps, which include a missing theoretical understanding of chain dynamics and how to distinguish effects of the particle dispersion and polymer chains. A holistic approach involving small-angle X-ray scattering (SAXS), dielectric spectroscopy (DS), and rheology, will be used to develop a theory based on recent progress to simultaneously describe the dielectric properties and rheology of polymer melts. Composites of NTPs (tethered chains on nanoparticles) dispersed in polymer matrices will be studied. The dispersion of the NTPs can be controlled by the grafting density, the molecular weight of free chains, and the corresponding characteristics of the NTPs. The static structure factor by SAXS can be used to obtain a phase map of systems with agglomerated and non-agglomerated particles, and to provide information on the length-scale of the confinement. The influence of the additional confinement imposed by nanoparticles on the chain dynamics will be explored, together with a change of the tube diameter of the polymer caused by surfaces.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.