Enhanced thermal diffusion in the vertical direction of flexible polyimide composite films with magnetically alignable h-BN platelets via ferrofluids hybridization

A facile approach is proposed to improve the anisotropic heat conduction of polyimide composite films containing hexagonal boron nitride (h-BN), thermally conductive filler with high anisotropy, via surface hybridization with ferrofluids as magnetic carrier source. The surfaces of the h-BNs were decorated with Fe3O4 particles to control their alignment using magnetic field. The h-BNs with hydroxyl groups (f-BN) were mixed with ferrofluids and heated to 130 °C with stirring. A considerable amount of Fe3O4 nanoparticles was attached to the surface of f-BNs, named mf-BNs. Flexible polyimide (PI) composite films were prepared by adding mf-BNs at 1-30 wt.% to investigate the anisotropic alignment of mf-BNs under magnetic field. The thru-plane thermal conductivity of the PI composite film with vertically aligned mf-BN of 30 wt.% is 6 times higher than that of the neat PI film, as increased from 0.212 to 1.246 W/m•K. This result is attributed to the anisotropic h-BN particles coated with the magnetic fluid arranged within the PI matrix in the vertical direction by using a neodymium magnet with less than 150 mT. This can solve the thermal issues of next-generation electronics by speeding the vertical heat transfer, which can greatly contribute to the improvement of the device reliability.