Molecular Dynamics of Oriented Elastomers and Crystalline Polymers Using Dielectric Spectroscopy

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.