Thermal conductivity of melt-processed nanofibers

Optimized thermal management remains a growing challenge for electronics packaging as increased heat fluxes must be dissipated through multiple material interfaces and as demand for smaller, flexible, and low-cost packages persists. Polymers are light weight and offer mechanical properties that make them favorable for thermal interface applications, but suffer from extremely low thermal conductivity. Here we melt polymer films into nanoporous anodic aluminum oxide (AAO) templates to fabricate large area arrays of vertically aligned polymer nanofibers. Nanoscale confinement and flow induced alignment effects improve polymer chain alignment and thermal conductivity along the fiber's long axis. Conjugated poly(3-hexylthiophene-2,5-diyl) (P3HT) and non-conjugated polyethylene (PE) of various molecular weights are explored to establish a relationship between polymer structure, nanofiber diameter, and the resulting thermal conductivity. In general, thermal conductivity improves with decreasing fiber diameter and increasing polymer molecular weight. Thermal conductivities approaching 10 W/m-K were achieved for both the 200 nm diameter PE fibers and the 100 nm diameter P3HT fibers. These results pave the way for optimization of the processing conditions to produce high thermal conductivity fibers using different polymers, which may be used in a broad range of thermal management applications.