Spatial gradients in dynamics of near-interface polymers: Experiments and theory

非技术概述近界面聚合物或界面聚合物是指在两相或两种组分之间的边界的纳米附近的聚合物。近界面聚合物的动力学和力学对各种纳米结构聚合物材料、聚合物纳米复合材料、聚合物薄膜和功能界面的设计和性能具有重要意义，这些材料在能源、环境、医疗保健、基础设施和可持续性等领域具有众多应用。例如，聚合物薄膜设计在数十亿美元的半导体工业中起着至关重要的作用。在许多情况下，在纳米界面附近的聚合物可以表现出弹性模量，粘度和扩散系数的大的空间变化（有时是数量级）。这个项目将解决的一个基本问题是负责这些大的变化和近界面聚合物动力学的空间依赖性的分子机制。通过提高我们对这些微观效应的理解，该项目将允许在界面处合理设计聚合物。该项目还将为研究生提供多种表征工具的培训，包括光谱学、流变学和小角度散射，并将为他们提供使用国家用户设施和建立专业联系网络的机会。此外，该项目通过吸引本科生来扩大研究参与，重点是通过兰辛学区（74%的人口是非洲裔美国人）和兰辛社区学院/密歇根州立大学2+2+2工程项目招募代表性不足的群体的学生。还将在研究生阶段实施关于界面聚合物的教育计划。一个K-12拓展活动模块将创建并通过密歇根州立大学K-12高中夏令营提供，以提高公众对聚合物和聚合物在interfaces.Technical SUMMARYThis项目的理解，旨在阐明近界面聚合物的动力学梯度及其对聚合物化学和纳米限制的依赖。与本体相比，界面处的聚合物可以表现出动力学和机械性能的深刻变化。这些变化可能涉及玻璃化转变的大位移（50 K），对应于结构弛豫时间的六到八十年的变化。然而，在量化的梯度界面动力学的缺陷提出了巨大的挑战和混淆的理解界面动力学及其与体玻璃化转变。一个全面的实验计划将量化的动态梯度在界面上，通过介电光谱，流变学和小角度散射的组合。将开发一种新的电介质标记系统，其精确放置在界面处，以在约1 nm的空间分辨率下量化近界面聚合物的动态。随着这一新的发展，PI的小组将进一步量化界面动力学梯度的确切函数形式以及聚合物化学和纳米限制对界面动力学梯度的影响。这些实验结果将提供现有的理论模型的关键测试，并有助于制定近界面聚合物dynamic.This奖项反映了NSF的法定使命的界面效应和纳米约束效应的定性描述，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

NON-TECHNICAL SUMMARYNear-interface polymers or interfacial polymers refer to polymers at the nanometer vicinity of a boundary between two phases or two components. The dynamics and mechanics of near-interface polymers can have strong implications for the design and performance of various nanostructured polymeric materials, polymer nanocomposites, thin polymer films, and functional interfaces which have numerous applications in areas such as energy, environmental, healthcare, infrastructure, and sustainability. For instance, thin polymer film design plays an essential role in the multi-billion dollar semiconductor industry. In many instances, the polymers at the nanometer vicinity of interfaces can exhibit large spatial variations (sometimes orders of magnitude) in elastic moduli, viscosity, and diffusion coefficient. A fundamental issue that this project will address is the molecular mechanisms responsible for these large variations and the spatial dependence of the near-interface polymer dynamics. By improving our understanding of these microscopic effects, this project will allow for the rational design of polymers at the interface. This project will also offer training for graduate students with multiple characterization tools, including spectroscopy, rheology, and small-angle scattering, and will provide opportunities for them to use national user facilities and build a network of professional contacts. Furthermore, the project expands research participation by engaging undergraduate students, with recruiting emphasis on students from underrepresented groups through the Lansing School District (74% population are African American) and the Lansing Community College/Michigan State University 2+2+2 Engineering Program. An educational program on polymers at the interfaces will also be implemented at the graduate level. A K-12 outreach-activities module will be created and delivered through MSU K-12 high-school summer camp to improve public understanding of polymers and polymers at the interface.TECHNICAL SUMMARYThis project aims to elucidate the dynamics gradients of near-interface polymers and their dependence on polymer chemistry and nanoconfinement. Polymers at the interface can exhibit profound alterations in dynamics and mechanical properties compared with the bulk. These changes can involve large shifts ( 50 K) in glass transition that correspond to six to eight decades of change in structural relaxation time. However, deficiencies in the quantification of gradients of interfacial dynamics impose grand challenges and obfuscate the understanding of interfacial dynamics and their connection with the bulk glass transition. A comprehensive experimental program will quantify the dynamics gradients at the interface through a combination of dielectric spectroscopy, rheology, and small-angle scattering. A new dielectric marker system will be developed with their precise placement at the interface to quantify the dynamics of the near-interface polymer at ~ 1 nm spatial resolution. With this new development, the PI’s group will further quantify the exact function forms of the interfacial dynamics gradient and the effects of polymer chemistry and nanoconfinement on the interfacial dynamics gradients. These experimental results will provide critical tests of existing theoretical models, and help to formulate a qualitative description of the interfacial effect and nanoconfinement effect for near-interface polymer dynamics.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.