Achieving Theoretical Property Limits in Polymer Nanofibers: Stiffness, Strength and Thermal Conductivity

Carnegie Mellon University, Pittsburgh PA

Investigators

Abstract

The objective of this award is to determine the degree to which the thermal and mechanical properties of nanoscale polymer fiber specimens can attain theoretical limits. Polymer materials are used in millions of consumer products even though their mechanical properties are relatively poor and their thermal conductivity is low. This is because long molecular chains tend to be disordered. However, the intrinsic stiffness, strength and thermal conductivity of polymers are high due to their carbon-carbon backbone. Using an ultra-high draw ratio technique, it now is possible to fabricate polyethylene nanofibers with a high degree of order. The approach in this work will be to employ a micromachined stepper motor to test ultra-drawn polymer mechanical properties. For the thermal conductivity measurements, a recently-developed six wire platform will be used. The benefit of this work is that it will enable assessment of polymer nanofiber for many applications. It is possible that properties near theoretical limits will be attained because the ultra-drawn fibers are highly ordered. Simultaneous high stiffness, strength and thermal conductivity values will in turn stimulate broad research. This will be in manufacturing techniques such as large scale nanofiber production, and in applications such as heat sinks, heat exchangers, body armor and composites. With regard to education, the investigators will expand two courses at Carnegie Mellon University. One will focus on mechanics and test methods of nanoscale specimens. The second will focus on thermal properties and develop metamaterial approaches to control them. Students in the investigators undergraduate course will be introduced to micromachined devices through a lecture and a portable "Class on a Chip" system. Grade 6-9 students will learn to program a micromachined device through an icon-driven interface. A Ph.D. student and two Master's Thesis students will gain expertise in both mechanical and thermal measurement techniques.