Transition of water transport mechanism in laminar graphene membrane with increasing thickness: Influence of strong cohesive interaction among water molecules

Stacked-graphene nanosheets have attracted significant attention as a new type of separation membrane due to their outstanding separation performance with unique physicochemical characteristics. Many studies have suggested that size exclusion dominates mass transport in stacked-graphene membranes, but the unique transport behavior of water has, up to now, not been adequately explained. In this study, we demonstrate that size-dependent diffusion (i.e. hindered diffusion) is the mechanism underlying transport evidenced by thermodynamic and molecular interaction analysis. Importantly, analysis based on solubility parameters (Hansen solubility parameters and Flory-Huggins parameters) in correlation with permeance revealed that molecular interactions play a key role to account for the distinct water transport behavior. Based on the interaction analysis, it was also discovered that the strong cohesive interaction leads to not only quasi-phase transition of water molecules in confined-nanochannel, but also transition of dominant mechanism from size-dependent to interaction-dependent with increasing thickness.