Interfacial Dynamics in Ultrathin Polymer Films

非技术摘要：在许多实际应用中，聚合物与固体表面直接接触，因此聚合物与衬底的相互作用和自由界面的存在会导致其体积性质的急剧偏离。我们仍然缺乏对这些偏差起源的基本理解。本研究将采用专门的介电、显微镜和热表征实验来深入了解纳米尺度约束和聚合物/表面相互作用对不同分子结构聚合物体性能的影响。这项工作的一个独特的焦点是开发新的，更准确的实验方法来探测聚合物和固体表面之间的直接界面的动力学。从计划中的研究中获得的基本理解可以为许多技术应用提供深思熟虑和优化聚合物设计的基础，例如电池，燃料电池和超级电容器，其中界面在决定整体功能方面起着重要作用。此外，从该项目中获得的关于与聚合物接触的固体表面的化学影响、聚合物的类型、限制范围和样品制备条件的知识将为聚合物科学和工程界提供基本的理解。这个项目的一个重要组成部分还包括若干综合教育活动。该项目将通过研究生和本科生积极参与这项研究，为聚合物纳米技术和材料科学专家的培训和教育做出贡献。综合研究/教育项目特别强调与代表性不足的群体合作，并为高中生提供研究经验。技术概述：由于界面结构和动力学的变化，聚合物在固体界面附近表现出与其体物理性质的偏差。这些变化导致微观弛豫时间分布的变化，这决定了聚合物材料的许多物理量，这些物理量与粘附、涂层和纳米复合材料等许多技术领域有关。对于聚合物性质的这些变化如何取决于分子结构、聚合物链的柔韧性、聚合物层的厚度、底物的化学性质以及温度的预测性理解仍然缺乏，而且直接探测受限聚合物微观动力学的可靠实验技术也是有限的。为了解决这一问题，计划中的项目将采用原子力显微镜，交流芯片量热法，特别是宽带介电光谱，结合最近开发的纳米结构电极组件，具有二氧化硅纳米结构和气隙，来探测模型超薄聚合物薄膜中的界面动力学。该项目的主要目标是揭示界面相互作用对线性和结构复杂聚合物的结构和链动力学的影响，超出平均松弛时间。主要目标包括：(i)对固体基质对界面处聚合物动力学的影响有一个基本的了解；（ii）阐明分子量、链柔韧性和结构对界面动力学的作用；(3)研究聚合物膜厚度和温度对界面弛豫时间分布的影响。从该项目中获得的对一维约束影响的详细基本理解将为设计具有独特性能的新型功能聚合物提供科学框架，这些聚合物适用于许多技术，包括涂料、聚合物复合材料、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，认为值得支持。

NON-TECHNICAL SUMMARY:In many practical applications, polymers are in direct contact with solid surfaces so that polymer-substrate interactions and the presence of free interfaces induce drastic deviations from their bulk properties. Fundamental understanding of the origins of these deviations is still lacking. This research will employ specialized dielectric, microscopy, and thermal characterization experiments to gain in-depth understanding of the impact of nanoscale confinement and polymer/surface interactions on the bulk properties of polymers of different molecular architectures. A unique focus of this work is the development of new, more accurate experimental methods for probing dynamics at the immediate interface between polymers and solid surfaces. The fundamental understanding obtained from the planned research could provide a basis for deliberate and optimal design of polymers for many technological applications, such as batteries, fuel cells, and supercapacitors, where interfaces play a significant role in determining the overall functionality. In addition, the knowledge gained from this project concerning the impact of the chemistry of solid surfaces in contact with polymers, the type of polymer, extent of confinement and sample preparative conditions will provide fundamental understanding to the polymer science and engineering communities. An important component of this project also involves several integrated educational activities. The project will contribute to training and education of specialists in polymer nanotechnology and materials science through active involvement of graduate and undergraduate students in this research. The integrated research/educational program particularly emphasizes work with underrepresented groups and research experiences for high-school students.TECHNICAL SUMMARY:Polymers exhibit deviations from their bulk physical properties in the vicinity of solid interfaces due to changes in interfacial structure and dynamics. These changes lead to shifts in the distribution of microscopic relaxation times determining many physical quantities of polymeric materials relevant to numerous technological fields as adhesion, coatings, and nanocomposites. Predictive understanding of how these alterations in the polymer properties depend on the molecular structure, flexibility of the polymer chains, thickness of the polymer layers, chemistry of the substrates, as well as temperature, is still lacking, and reliable experimental techniques to directly probe the microscopic dynamics in confined polymers are limited. To address this gap, the planned project will employ atomic force microscopy, AC chip calorimetry, and especially broadband dielectric spectroscopy in combination with recently developed nanostructured electrode assembly featuring silica nanostructures and an air gap, to probe interfacial dynamics in model ultrathin polymer films. The main goal of the project is to unravel the impact of interfacial interactions on structural and chain dynamics in linear and architecturally complex polymers, beyond the mean relaxation times. The major objectives include: (i) to develop a fundamental understanding of the influence of solid substrates on dynamics of polymers at interfaces; (ii) elucidate the role of molecular weight, chain flexibility, and architecture on interfacial dynamics; and (iii) investigate the impact of polymer film thickness and temperature on the distribution of relaxation times at the interphases. The detailed fundamental understanding of the impact of one-dimensional confinement gained from this project will provide a scientific framework for the design of novel functional polymers with unique properties for numerous technologies, including coatings, polymer composites, and polymer electrolytes suitable for use in electrochemical power sources and devices..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.