Understanding the Impact of Confinement on the Dynamics of Entangled Chains

非技术总结：塑料材料（聚合物）的多样性和灵活性改变了我们的生活。尺寸小至十亿分之一米的颗粒（纳米颗粒）的出现可以提供具有上级性能的甚至更柔韧和更坚固的材料，因为数十亿个这些颗粒可以被掺入聚合物中以产生纳米复合材料。 现代化学可以在分子水平上对这些纳米粒子进行修饰，从而对其材料行为产生重大影响，通常具有未知和新颖的特性。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实现这一任务。然后将使用先进的实验技术研究在这些条件下的纳米粒子约束的影响。 该项目包括理解纳米复合材料的机械性能与纳米颗粒的空间分布之间的关系，以及在分子长度尺度上的理论描述。 本研究还结合了学生的教育，使他们接触到各种先进的实验technology.Technical摘要：在本研究中，将研究纳米限制对聚合物熔体的影响。 重点将放在纳米粒子的分散，表面和链接枝到表面的影响链动力学的操纵。目前的理解是有限的知识差距，其中包括缺乏理论上的理解链动力学和如何区分颗粒分散和聚合物链的影响。一个整体的方法，涉及小角X射线散射（SAXS），介电谱（DS）和流变学，将被用来开发一个理论的基础上，最近的进展，同时描述聚合物熔体的介电性能和流变学。将研究分散在聚合物基质中的NTPs（纳米颗粒上的拴系链）的复合材料。NTPs的分散性可以通过接枝密度、自由链的分子量和NTPs的相应特性来控制。通过SAXS的静态结构因子可以用于获得具有团聚和非团聚颗粒的系统的相图，并提供关于约束的长度尺度的信息。将探讨纳米粒子对链动力学施加的额外限制的影响，以及由表面引起的聚合物管径的变化。该奖项反映了NSF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.