Ultrathin Super-Barrier Film Via 100 % Surface Coating Coverage of Self-Assembled Graphene Oxide Sheets

Although graphene-based materials have been projected to be impervious even to Nature's smallest molecule, He, so far graphene-based barriers have exhibited a rather high water vapor transmission rate (WVTR) of 10 -1 – 10 -2 g/m 2 ·day. This disparity stems from the abundant nano- and micron-scale defects in graphene basal planes, which typically function as shortcuts or highways for water diffusion through the tortuous layers of graphene-based sheets. Here WVTR of 4.1 × 10 -5 g/m 2 ·day and lag time of 1 month (730 hours) are demonstrated in a tortuously nanostructured thin film solely consisting of reduced graphene oxide (rGO) sheets, approaching the WVTR toward the theoretical impermeability. Effective design principles proven for this ultrathin super-barriers are (i) tortuous nanostructure, (ii) 100 % surface coverage, (iii) > 35 μm lateral size of the building block graphene oxide (GO), (iv) suppressed defect density during production of GO, (v) surface hydrophobization, and (vi) interlayer distance narrowing down to 0.367 nm. These design principles consistently follow one simple rule: blockage of all possible water diffusion pathway. Also, it is proven here that such impermeability can be actualized by scalable layer-by-layer assembly process, which can shed a light for mass-produced super-barriers for flexible electronics in the near future