Molecular Dynamics of Oriented Elastomers and Crystalline Polymers Using Dielectric Spectroscopy

技术综述：本项目的重点是单轴机械应变下聚合物材料分子动力学的基础研究。宽带介电光谱学是一种强大但出人意料的未得到充分利用的技术，将被用作在广泛的温度和频率范围内动态变化的实验探头。了解聚合物材料在变形状态下的分子迁移率对于它们在薄膜、取向带和纤维中的成功应用至关重要。然而，以往关于机械变形对聚合物动力学的研究很少，使用宽带介电光谱的研究也很少。本研究的总体目标是深入了解单轴变形对选定的交联型和热塑性弹性体以及选定的半结晶聚合物的动力学的影响。为了以一种全面的方式做到这一点，关键是要彻底表征伴随变形而来的分子取向和结构变化。对于弹性体，将根据实验测量的取向函数和任何应变诱导结晶来开发分子水平的解释。为了详细了解所观察到的变形半结晶聚合物的松弛行为，必须表征伴随变形而发生的重大微观结构变化。我们将使用各种方法，包括广角和小角X射线散射技术，通过实验来跟踪微观结构的变化和分子取向。非技术概述：这个项目涉及聚合物体系变形时分子迁移率变化的基础研究，这对聚合物薄膜、涂层和纤维的生产和成功的工业应用至关重要。宽带介电光谱学是一种强大但出人意料的未得到充分利用的技术，它将被用来测量分子在不同程度拉伸时的运动变化。与其他实验方法的结果一起，将开发分子水平的解释，促进这些材料的高级应用。该研究计划将为研究生和本科生以及博士后创造新的学习机会。本科生将通过高级顶石项目以及宾夕法尼亚州立大学由NSF支持的REU项目参与。所有参与者将继续参与外联活动，特别是与宾夕法尼亚州立大学S在科学和工程学院6-12年级的教育经验有关的活动。

TECHNICAL SUMMARY:The focus of this project is the fundamental investigation of the molecular dynamics of polymeric materials under uniaxial mechanical strain. Broadband dielectric spectroscopy, a powerful but surprisingly underutilized technique, will be used as the experimental probe of the dynamics over a broad range of temperatures and frequencies. An understanding of molecular mobility of polymeric materials in the deformed state is critical to their successful application in films, oriented tapes, and fibers. Nevertheless, there have been only a modest number of previous investigations of mechanical deformation on polymer dynamics, and very few using broadband dielectric spectroscopy.The overall objective of this study is to develop basic insight into the role of uniaxial deformation on the dynamics of selected crosslinked and thermoplastic elastomers, as well as selected semi-crystalline polymers. In order to do so in a comprehensive fashion, it is critical that molecular orientation and structural changes accompanying deformation be thoroughly characterized. For elastomers, molecular level interpretations will be developed, in light of the experimentally measured orientation function and any strain-induced crystallization. To develop a detailed understanding of the observed relaxation behavior of deformed semi-crystalline polymers, the significant microstructural changes accompanying deformation must be characterized. Microstructural changes and molecular orientation will be followed experimentally using a variety of methods, including wide- and small-angle X-ray scattering techniques.NON-TECHNICAL SUMMARY:This project concerns the fundamental investigation of changes in molecular mobility as polymer systems are deformed, of critical importance to the production and successful industrial application of polymer films, coatings and fibers. A powerful but surprisingly underutilized technique, broadband dielectric spectroscopy, will be used to measure changes in molecular motions at various degrees of stretching. Together with findings from other experimental methods, molecular-level interpretations will be developed, facilitating the tailoring of these materials for advanced applications.The research program will create new learning opportunities for graduate and undergraduate students, as well as a post-doctoral fellow. Undergraduate students will participate through a senior capstone project, as well as through an NSF supported REU program at Penn State. All participants will continue to engage in outreach activities, particularly those connected with Penn State?s Women In Science and Engineering Institute grade 6 ? 12 educational experiences.