WFU Department of Physics Wake Forest University

 

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WFU Physics Ph. D. Thesis Defense

TITLE: Carbon Nanotube Based Organic Thermoelectric Composites: Synthesis, Characterization, Performance

SPEAKER: Corey Hewitt,

Department of Physics
Wake Forest University

TIME:Tuesday December 3, 2013 at 9 AM

PLACE:Room 103 Olin Physical Laboratory

All interested persons are cordially invited to attend.


ABSTRACT

The performance of thermoelectrics has seen little improvement over that of the most commonly used material bismuth telluride since its discovery sixty years ago. In recent years, slight improvements through the use of complex crystalline structures have renewed interest in thermoelectrics, however, their performance is still orders of magnitude below that required to replace current heat engine power sources. One potential solution is to consider using thermoelectrics in low powered applications where their efficiencies are comparable to those of standard heat engines.

Carbon nanotube based polymer composites possess several properties that make them ideal for use in low powered waste heat recovery applications. The favorable thermoelectric properties of the carbon nanotubes with moderate Seebeck coefficients and potentially large electrical conductivities result in modest power factors, while the low thermal conductivity of the polymer host aids in maintaining a temperature gradient across the composite thus improving the figure of merit. Although the thermoelectric performance of these composites is lower than that of standard crystalline thermoelectrics, their light weight and flexible physical structure makes them more ideal for use in personal and portable electronics that utilize waste heat to maintain a temperature gradient.

In order to effectively utilize a thermoelectric material in a practical application, they must be combined in a device structure consisting of alternating p-type and n-type elements that are connected electrically in series and thermally in parallel. Here, we introduce a novel device architecture suited to using the thin film carbon nanotube based polymer composites. The device performance is then dictated by the intrinsic thermoelectric properties of the individual layers composing the device. Therefore, the majority of the work presented here focuses on understanding the effects of carbon nanotube synthesis and processing parameters, and extrinsic factors on the thermoelectric properties of the composites. By quantifying these effects, the thermoelectric performance of the individual layers can be optimized in order to increase the total power output of the device. Ultimately however, the total power output is limited by the specific application; therefore, power output measurements versus several application parameters are performed.



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100 Olin Physical Laboratory
Wake Forest University
Winston-Salem, NC 27109-7507
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