Enhancing Thermal Transport Properties of Nanocomposites

Composite materials have long been considered a panacea for improved performance and reliability of aerospace structures because of their presumed high strength and light weight. Therefore, it is not a surprise that many divisions across NASA have been exploring various types of composite materials for different applications. In the past two decades, nanocomposite materials, i.e., composites with nanofillers, have attracted significant attention because of the unique and tunable properties of these materials. In particular, nanocomposites with carbon nanotubes (CNTs) as fillers have attracted a great deal of attention due to the superior properties of CNTs. One particular issue for CNT-based composite materials is the challenge to achieve desirable thermal conductivity enhancement. Tremendous efforts following the traditional "mix and measure" approach have all failed to achieve the expected high thermal conductivity predicted based on the particle mixing theory. These results point to a lack of fundamental understanding of thermal and mechanical coupling at the junctions between CNTs and at the interfaces between CNTs and host materials, which cannot be obtained from the traditional "mix and measure" approach. Driven by my inherent curiosity of pursuing deep understanding of the underlying physics of things and based on a unique technology that can examine thermal coupling at individual nanoscale contacts, here I propose to explore the contact thermal resistance between CNTs of different morphologies and between CNTs and different host materials. The proposed study is totally different from the traditional "mix and measure" approach and will yield solid experimental data to disclose how energy carriers transport at the nanoscale contacts, which will provide the urgently-needed insights for improving the thermal conductivity of CNT-based composites. Based on the knowledge acquired from studying thermal transport through contacts between CNTs and interfaces between CNTs and host materials, we will design and fabricate CNT-polymer composite materials with desirable contact morphology between CNTs. We will prepare these CNT-polymer composites as nanofibers through electrospinning, which should allow us to vary the embedded CNT concentration and CNT alignment by tuning the fabrication parameters. Both thermal and mechanical properties of resulting fibers will be examined to correlate with the fundamental understanding we obtained from measuring the contact thermal resistance between individual CNTs. We expect that through these systematic studies, we will be able to provide new design rules that can lead to CNT- polymer composites with superior thermal and mechanical properties. Ultimately, the proposed project will lead to new high performance composite materials with a broad range of applications important to NASA. Managing thermal load is a common issue in various components of NASA space vehicles, such as the structural materials of rockets or the engine combustion chambers. NASA has spent more than a decade of intense efforts on using CNTs to enhance the thermal conductivity of various composites with limited success. The proposed research directly tackles the problem from a totally different angle and will pave a new route to achieve the goals of NASA researchers in terms of creating CNT-based nanocomposites with tunable thermal and mechanical properties.

The proposed research will pave a new route to achieve the goals of NASA researchers in terms of creating CNT-based nanocomposites with tunable thermal and mechanical properties. Composite materials have long been considered a panacea for improved performance and reliability of aerospace structures because of their presumed high strength and light weight.

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