Interfaces act as barriers for thermal transport. Thermal interface materials (TIMs) optimize interfacial contact and increase heat conduction through the interface. Fundamentally a TIM must be a thin layer with high through-thickness thermal conductivity. TIMs fill the micro-roughness between adjoining surfaces. Aligned multiwall carbon nanotube (MWCNT) arrays are ideal candidates for a TIM application, with high axial thermal conductivity (650 - 830 W/mK), low array density (0.2 g/cm~3), elastic compressibility (buckling), negligible volatility, and high thermal stability. Here we report a comparison between the thermal performance at elevated temperatures of a "dry", free-standing vertically-aligned MWCNT array TIM and a commercial thermal grease. The arrays contain no polymeric binder, thus permanent bonding and viscous flow or pump-out are not of concern and simultaneously preserve resistance to high vacuum and temperature. Two-layer Al disc sandwiches, compressed at varying pressures, with MWCNT array and thermal grease TIMs were characterized using laser flash for thermal diffusivity and interfacial contact resistance (Netzsch LFA 427). Additional thermal cycling and high vacuum (10~(-5) mbar) measurements were performed.
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