Fabricating high thermal conductivity rGO/polyimide nanocomposite films via a freeze-drying approach

The preparation of polymeric composite materials with low filler content as well as high thermal conductivity has been an important subject for the field of polymer material research. During our recent investigation on polyimide (PI), it was found that poly(amic acid) (PAA) solution (in dimethylacetamide, DMAc) could crystallize at low temperature. When adding reduced graphene oxide (rGO) as the thermal conductive fillers in the PAA solution, it was also found that the crystallization process of PAA would impel the rGO to rearrange in order and form an aligned thermal conductive network. To retain the rGO network structure, the freeze-drying technique was used to remove the solvent. Subsequently, through a thermal imidization process the final rGO/PI films containing a 3D rGO network could be obtained. The PI composite films retain good flexibility, excellent thermal stability, and exhibit excellent thermal conductivity. When the content of rGO added is 8 wt%, the thermal conductivity of the rGO/PI film can reach a high value of 2.78 W m^-1 K^-1, which is about 15.4 times that of neat PI and 5.5 times that of the rGO/PI composite film prepared by the conventional two-step routine with the same content of rGO.