Collaborative Research: Understanding and Controlling the Mechanical and Thermal Properties of Polymer Nanofibers

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Polymers find ubiquitous applications in modern civilization. However, polymers are generally regarded as poor heat conductors, while many applications would benefit from polymer materials that are able to function as good heat conductors. Recent studies have suggested polymer materials that have been significantly stretched could have substantially enhanced mechanical strength and heat conduction. We therefore aim to study the mechanical and thermal properties of nanoscale fibers formed in a jet that induces significant stretching. We expect that heat transport in these nanofibers may be profoundly enhanced compared to larger, unstretched versions of the same polymer. We will study how the jet stretches the polymer molecules, and how the resulting molecular orientation in turn results in enhanced mechanical strength and heat conduction, which may eventually lead to exciting new polymer materials that are extremely strong, flexible, and good conductors of heat. Such materials would enable a variety of applications, such as flexible electronics and displays, solar cells, and advanced structural materials integrated with high-power electronics, leading to significant future technological advancements. The project has integrated research and educational components to train graduate students in an interdisciplinary environment, and to extend the impact to underrepresented minorities through collaboration between Vanderbilt and Fisk universities.This project aims to correlate the manufacturing process conditions, structure, as well as mechanical and thermal properties of electrospun polymer nanofibers. The approach is to integrate informed control of the electrospinning process, mechanical and thermal transport property measurement, thorough microstructural characterization, and theoretical analysis to achieve an in-depth understanding of how electrospinning parameters affect nanofiber microstructure, mechanical and thermal properties. The structure and property characterization will be performed at an individual nanofiber level, thereby avoiding averaging over potential fiber heterogeneity. Microstructure will be characterized using micro-Raman spectroscopy, a technique which is able to provide detailed information about molecular composition and orientation from a small sample volume. Mechanical properties of individual nanofibers will be characterized using an atomic force microscope to perform a 3-point bend test. Thermal properties of individual nanofibers will be measured using custom-built microdevices. With an understanding of how electrospinning parameters affect microstructure, and the interplay between microstructure and mechanical/thermal properties, we will be able to optimize deposition parameters to achieve polymeric materials with tunable mechanical and thermal properties.