SUBJECT: Ph.D. Dissertation Defense
BY: Thomas Bougher
TIME: Friday, October 23, 2015, 1:00 p.m.
PLACE: MRDC Building, 4211
TITLE: Photothermal Characterization of Thermal Transport in Carbon Nanotubes and Nanostructured Polymers
COMMITTEE: Dr. Baratunde Cola, Chair (ME)
Dr. Samuel Graham (ME)
Dr. Satish Kumar (ME)
Dr. Mark Losego (MSE)
Dr. Chuck Zhang (IYSE)


As the size of electronics continue to decease and the power density continues to increase, the role of thermal management for electronics becomes increasingly important. To this end a variety of organic materials are employed with the aim of achieving higher thermal conductivity. The three main classes of materials used in this work are: vertical arrays of polymer nanotubes, polymer thin films, and vertical arrays of carbon nanotubes (CNTs). Vertically aligned arrays of polymer nanotubes are synthesized through electrochemical polymerization and melt processing. In both cases the vertically aligned arrays are created using a nanoporous template with pore sizes ranging from 50 to 200 nm. It is found that the nanopores induce alignment of polymer chains in the direction of the pore axis, which increases the thermal conductivity to more than 20 times that of bulk. The vertical arrays of polymer nanotubes are joined to opposing surfaces to create thermal interface materials (TIMs) and the total thermal resistance is measured using the photoacoustic technique. The total resistance of polymer TIMs was as low as 10 mm²-K/W and demonstrated to be thermally stable at elevated temperatures. In addition, the thermal conductivity of conjugated polymer thin films is measured for thin (~100 nm) films and thick (~10 μm) films under various processing and doping conditions. It is found that highly anisotropic electrical conductivity leads to erroneous predictions of through-plane thermal conductivity based upon the Wiedemann-Franz law. Modifications of the photoacoustic technique and TDTR are demonstrated for measurement of CNT thermal conductivity and contact resistance. These techniques are used to characterize vertically aligned CNT forests infiltrated with a conducting polymer. This composite was found to reduce the total thermal resistance of CNT TIMs to as low as 2 mm²-K/W.