Controlling thermal conductivities and electrical insulation properties of carbon nanofiber/polyimide composites using surface coating techniques

Abstract In the present work, sandwich‐structured composite sheets consisting of a core layer of carbon nanofiber (CNF)/polyimide (PI) and an outer layer of either pristine PI or hexagonal boron nitride (hBN)/PI were proposed and characterized for the possibility that they could enhance the effective thermal conductivity (TC) of PI composite sheets while also retaining their electrical insulation properties. The sandwiched structures were prepared using a dip coating method. The electrical insulation properties were evaluated via the breakdown voltage (BDV) of direct current. By using hBN with an average size of 0.5 μm as filler for the outer layer, a composite sheet with a highly effective level of TC was prepared. The BDV achieved more than 2 kV, when the outer layer had a total thickness of approximately more than 60 μm even at 30 vol% of hBN_0.5 content. The tensile strengths of the sandwich‐structured sheets indicated the values between each single layer of the 10 vol%‐CNF/PI and hBN_0.5/PI composites.