Layer-by-layer assembly of graphene on polyimide films via thermal imidization and synchronous reduction of graphene oxide

To investigate the effects of holding time after deposition of polyethylenimine (PEI) solution and molecular weight of PEI on the surface morphology of multi-layer films prepared by layer-by-layer (LbL) method, polyamic acid (PAA)/PEI/graphene oxide (GO) films were prepared using different holding times and different molecular weights of PEI. To convert PAA into polyimide (PI), the films were thermally imidized after film deposition. In this process, GO was also converted into partially reduced GO (rGO). The effects of holding time and molecular weight of PEI on the surface morphology and the sheet resistance of PI/PEI/rGO films were investigated. Also, to investigate the effect of rGO on the barrier properties of PI based multilayer films, (PI/PEI/rGO/PEI)(6) films were prepared by LbL method. Longer holding time (10 min) and smaller molecular weight (25,000) of PEI lead to relatively flat surfaces, but shorter holding time (5 min) and larger molecular weight (75,000) result in wrinkled and overlapped surfaces. The sheet resistance of PI/PEI25K/rGO films prepared with holding time 10 and 5 min is 502.1 k Omega/sq and out of range (> 2000 k Omega/sq), respectively. The sheet resistance of PI/PEI75K/rGO films prepared with holding time 10 min is out of range (> 2000 k Omega/sq). Gas transmission rate (GTR) and permeability coefficient of (PI/PEI25K/rGO/PEI25K)(6) are lower than those of (PI/PEI75K/rGO/PEI75K)(6), respectively.