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

近界面聚合物或界面聚合物是指在两相或两组分之间的纳米边界附近的聚合物。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、基础设施和可持续发展等领域有着广泛的应用。例如，聚合物薄膜的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在弹性模量、粘度和扩散系数方面表现出很大的空间变化（有时是数量级）。该项目将解决的一个基本问题是导致这些大变化的分子机制以及近界面聚合物动力学的空间依赖性。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，通过兰辛学区（74%的人口是非裔美国人）和兰辛社区学院/密歇根州立大学2+2+2工程项目，重点招收来自代表性不足群体的学生。一个关于聚合物界面的教育项目也将在研究生阶段实施。通过密歇根州立大学K-12高中夏令营，将创建一个K-12外展活动模块，以提高公众对聚合物和聚合物界面的理解。本项目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约束的依赖。与本体相比，界面处的聚合物在动力学和力学性能上表现出深刻的变化。这些变化可能涉及玻璃化转变的大位移（50 K），对应于60到80年的结构弛豫时间变化。然而，界面动力学梯度量化的不足给界面动力学及其与体玻璃化转变的关系的理解带来了巨大的挑战和模糊。一个全面的实验程序将通过介电光谱、流变学和小角度散射的组合来量化界面上的动力学梯度。将开发一种新的介电标记系统，将其精确放置在界面上，以量化近界面聚合物在~ 1nm空间分辨率下的动力学。有了这一新的发展，PI的团队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。这些实验结果将为现有理论模型提供关键测试，并有助于对近界面聚合物动力学的界面效应和纳米约束效应进行定性描述。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 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.