SUBJECT: Ph.D. Proposal Presentation
BY: Thomas Bougher
TIME: Friday, December 19, 2014, 1:00 p.m.
PLACE: Love Building, 109
TITLE: Thermal Transport in Nanostructured Organic Materials
COMMITTEE: Dr. Baratunde Cola, Chair (ME)
Dr. Samuel Graham (ME)
Dr. Satish Kumar (ME)
Dr. Mark Losego (MSE)
Dr. Chun (Chuck) Zhang (IYSE)


As the size of electronics continues to decease, the role of thermal management for electronics becomes increasingly important. To this end a variety of organic materials are employed with various synthesis and processing techniques aimed at improving the thermal conductivity of these materials. The three main classes of materials used in this work are: vertical arrays of carbon nanotubes (CNTs), vertical arrays of polymer nanotubes, and polymer thin films and composites with CNTs. Individual carbon nanotubes possess high thermal conductivity although when grown in a vertical array their thermal conductivity is drastically reduced. A method for the direct measurement of the effective thermal conductivity of CNT arrays is developed and demonstrated on arrays with different growth conditions. The thermal and electrical transport between CNTs and conjugated polymers is investigated using polymer bonding of CNT arrays and CNT-polymer composites.
In addition, vertically aligned arrays of polymer nanotubes are synthesized through a variety of techniques including electrochemical polymerization, solution processing, and melt processing. In all cases the vertically aligned arrays are created using a nanoporous template with pore sizes ranging from 50 to 200 nm. It is found that in many cases the nanopores create alignment of polymer chains in the direction of the pore axis, which creates large enhancements in thermal and electrical conductivity. The smaller diameter tubes also have the highest thermal conductivity as measured by the suspended microbridge technique. 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 TIMs created with optimal processing conditions are found to compare favorably with a range of commercial materials and are also shown to be thermally stable at elevated temperatures.
Lastly a number of polymer thin films are measured using Time Domain Thermoreflectance (TDTR) and the photoacoustic technique and the difference in thermal conductivity for thin (~100 nm) films in TDTR and thick (~10 μm) is examined as a function of processing and structure. The relationship between thermal and electrical transport in these films is investigated, and a new technique of TDTR data analysis is presented allowing greater confidence in extracting material properties.