Mechanistic investigation of organic layers in graphene-based gas barriers

Self-assembled organic layers containing various functional groups between graphene layers were examined as gas barrier films. The formation of well-defined self-assembled layers of functionalized alkane molecules on graphene was confirmed by scanning tunneling microscopy (STM). The roles of these organic layers as gas barrier films could be quantitatively deduced by comparing their water vapor transmission rate (WVTR). The formation of self-assembled layers dramatically improved gas barrier properties by primarily blocking defects and gas molecule pathways. For functionalized alkanes containing hydrophilic groups, more enhanced gas barrier properties were observed compared to those with hydrophobic groups. These results clearly indicate that the primary role of the organic layers in gas barrier films is to block defects and the pathways of water molecules, with a secondary role of delaying the movement of water molecules through hydrogen bonding interactions.