Vertically oriented carbon nanotube (CNT) arrays can increase real contact in thermal interfaces and efficiently transfer heat between the mating solids. In this study, a paraffin wax that changes phase at approximately 50°C was applied to interfaces with CNT arrays directly synthesized on one side of the interface, and to foil/CNT interfaces with CNT arrays directly synthesized on one side and both sides of the foil. The bulk thermal resistances of single-sided CNT array/wax interfaces were measured using a transient photoacoustic (PA) technique to range from approximately 2 to 3 mm~2-K/W under moderate pressures. The bulk thermal resistances of foil/CNT/wax interfaces were measured with the PA technique to range from approximately 10 to 20 mm~2-K/W under moderate pressures. For each sample structure, the addition of paraffin wax to the CNT arrays produced significant reductions in thermal resistance. We surmise that this improved thermal performance could be a function of the wettability of paraffin wax to CNTs. A hydrophilic wetting angle of approximately 47° was observed at the interface of liquid wax and the free tips of a CNT array at 60°C, and field-emission scanning electron microscope images taken after PA testing revealed individual CNTs that were blanketed with a wax coating.
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