Quantifying the Polymer Physics of Mechanical Deformation in Ultra-thin Polymer Glasses

非技术概述许多技术依赖于聚合物薄膜的特性和性能。例如，清洁水应用中使用的膜由薄的聚合物层组成，水被推过这些层以分离和去除不需要的污染物。尽管目前有用，但由于聚合物薄膜的机械强度方面的工程限制，这项技术在能量上仍然是不利的。除了薄膜之外，许多其他应用的效率和寿命也受到聚合物薄膜的机械性能的限制；然而，对薄膜中这些性能的直接了解极其有限。当聚合物材料被加工成只有几个分子厚度的薄膜时，它们的变化是众所周知的，但这些变化如何影响机械强度仍不清楚。拟议的项目将通过直接测量超薄聚合物的机械性能来克服当前的挑战，产生新的基础数据和知识，这些数据和知识可以帮助指导设计和合成新材料，以获得更好的膜、替代电源以及许多其他技术。本研究将为研究生和本科生复合型人才的培养奠定坚实的基础。为了将这个项目的影响扩展到K-12教育水平，将开发新的材料科学和工程课程材料，并将其整合到一个名为BioInspire！的研讨会中。本课程的目的是在生物启发的创新背景下教授材料科学、工程和生物学的课程，其中科学、工程和艺术可以被用来吸引广泛的、不同的学生群体。技术总结本项目将发展与聚合物玻璃超薄薄膜的机械性能相关的聚合物物理的基础知识。尽管玻璃聚合物链在表面主导区的迁移率变化已被广泛研究，但对超薄聚合物膜的力学性能的研究还很有限。在这里，一种新的测量设备，称为超薄薄膜拉伸测试仪(UFT)，将被用来测量聚合物薄膜在单轴拉伸条件下的全应力-应变关系。通过在较宽的应变和温度范围内通过单调和循环加载历史来量化弹性和耗散过程，以及在尺寸约束区域中进行受控断裂实验，所提议的测量将提供对超薄聚合物薄膜中的力学响应的完整理解。将研究三种材料体系，包括聚苯乙烯(PS)、聚碳酸酯(PC)和聚苯乙烯/聚(2，6-二甲基-1，4-苯氧基)(PS/PPO)共混物，从而实现对分子结构和力学响应的系统调节。这些发现有望为以下方面提供新的见解：表面附近聚合物迁移率的变化如何改变聚合物的本构响应；尺寸几何约束引起的纠缠密度的变化如何改变断裂机制；以及聚合物分子上的几何约束如何改变耗散或塑性变形的开始。该项目的发现将对基础聚合物物理以及新的表征方法的开发产生重大影响，这些方法可以帮助开发用于薄膜应用的先进材料。

NON-TECHNICAL SUMMARY Numerous technologies rely upon the properties and performance of thin polymer films. For example, membranes used in clean water applications are comprised of thin polymer layers through which water is pushed to separate and remove unwanted contaminants. Although currently useful, this technology remains energetically unfavorable due to engineering limits with regard to the mechanical strength of polymer thin films. Beyond membranes, the efficiency and lifetime of many other applications are also limited by the mechanical properties of polymer thin films; however, direct knowledge of these properties in thin films is extremely limited. Changes in polymer materials when they are processed into films comprised of only a few molecules in thickness are well known, but how these changes impact mechanical strength remains unclear. The proposed project will overcome current challenges with directly measuring mechanical properties in ultra-thin polymers, leading to new fundamental data and knowledge that can help guide the design and synthesis of new materials for better membranes, alternative power sources, as well as many other technologies. The proposed research will provide a strong foundation for the education and training of multiple graduate students and undergraduate researchers. To extend the impact of this project to the K-12 education level, new materials science and engineering curriculum materials will be developed to be integrated into a workshop, called BioInspire!. This program is designed to teach lessons of materials science and engineering and biology in the context of bioinspired innovation, where science, engineering, and art can be used to engage a broad, diverse group of students.TECHNICAL SUMMARYThis project will develop fundamental knowledge of the polymer physics associated with the mechanical properties in ultra-thin films of polymer glasses. Although changes in the mobility of glassy polymer chains in a surface-dominated regime has been studied extensively, the mechanical properties in ultrathin polymer films have only been studied to a limited extent. Here, a new measurement device, called the Ultrathin Film Tensile tester (UFT), will be used to measure the complete stress-strain relationship for polymer thin films under uniaxial extension conditions. The proposed measurements will provide a complete understanding of mechanical responses in ultra-thin polymer films by quantifying elastic and dissipative processes through monotonic and cyclic loading histories across a wide strain and temperature range, as well as controlled fracture experiments in the dimensionally-constrained regime. Three materials systems, including polystyrene (PS), polycarbonate (PC), and blends of polystyrene and poly(2,6-dimethyl-1,4-phenylene oxide) (PS/PPO), will be studied, allowing molecular structure and mechanical responses to be tuned systematically. The findings are expected to provide new insight with regards to how polymer mobility changes near a surface can alter the constitutive response of a polymer, how changes in entanglement density due to dimensional geometric constraints alters fracture mechanisms, and how geometric constraints on polymer molecules may alter the onset of dissipative or plastic deformations. The findings from this project will have a significant impact on fundamental polymer physics, as well as on the development of new characterization methods that can aid the development of advanced materials for thin film applications.