Interfacial Dynamics in Ultrathin Polymer Films

非技术总结：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-基材相互作用和自由界面的存在会导致其整体性质发生剧烈变化。对这些偏差的起源仍然缺乏基本的了解。这项研究将采用专门的介电，显微镜和热表征实验，以深入了解纳米级限制和聚合物/表面相互作用对不同分子结构聚合物的整体性能的影响。这项工作的一个独特的重点是开发新的，更准确的实验方法，用于探测聚合物和固体表面之间的直接界面的动力学。从计划的研究中获得的基本理解可以为许多技术应用（如电池，燃料电池和超级电容器）的聚合物的精心和优化设计提供基础，其中界面在确定整体功能方面发挥着重要作用。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，聚合物类型，限制程度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。该项目的一个重要组成部分还涉及若干综合教育活动。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/教育计划特别强调与代表性不足的群体和高中生的研究经验的工作。技术概要：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本体物理性质的偏差。这些变化导致微观弛豫时间分布的变化，这些变化决定了与粘合、涂层和纳米复合材料等众多技术领域相关的聚合物材料的许多物理量。预测了解这些变化的聚合物的性质如何取决于分子结构，聚合物链的灵活性，聚合物层的厚度，基板的化学性质，以及温度，仍然缺乏，可靠的实验技术，直接探测在受限的聚合物的微观动力学是有限的。为了解决这一差距，计划中的项目将采用原子力显微镜，AC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空气间隙，以探测模型聚合物薄膜的界面动力学。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，超越平均弛豫时间。主要目标包括：（i）发展一个基本的理解的影响，固体基板上的动态聚合物在接口;（ii）阐明分子量的作用，链的灵活性，和结构上的界面动力学;和（iii）调查的影响聚合物膜的厚度和温度上的弛豫时间的分布在界面。从该项目中获得的对一维限制影响的详细基本了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，用于多种技术，包括适用于电化学电源的涂层、聚合物复合材料和聚合物电解质和设备。该奖项反映了NSF的法定使命，并被认为是值得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的支持。

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.