Porous boron nitride/polyimide composite films with high thermal diffusivity and low dielectric properties via high internal phase Pickering emulsion method

[Display omitted] •Porous boron-nitride/polyimide (BN/PI) composites are fabricated via high internal phase Pickering emulsion (HIPPE).•BN nanoparticles were uniformly dispersed on the surface of porous PI skeleton.•3D-connected BN nanoparticles on the surface of PI skeleton act as an efficient heat transfer path.•Internal porous structure of BN/PI composite films enable to exhibit the extremely low dielectric properties. This work offers a simple fabrication of porous boron-nitride-(BN)/polyimide-(PI) composite films with high thermal diffusivities and low dielectric constants by combining high-internal-phase Pickering emulsification (HIPPE) and subsequent hot-pressing. BN nanoparticles in composite foams were well dispersed and three-dimensionally connected following the surface of the PI skeleton used as the polymer matrix. The BN contents in the BN/PI composite foams were adjusted in the range of 20–80wt%. The porosities of the composite films were controlled according to the hot-pressing conditions such as the temperature. The porous BN/PI composite films exhibited high thermal diffusivities of 0.059–1.033mm2/s and low dielectric constants of 2.08–3.48 at 1GHz for BN contents of 20–80wt%. In particular, the BN/PI composite films had extremely low dielectric loss values, close to zero (