Segregation Structures and Miscellaneous Diffusions for Ethanol/Water Mixtures in Graphene-Based Nanoscale Pores

Molecular dynamics simulation was conducted to study ethanol water mixtures and the corresponding pure species, confined within slit-shaped graphene nanopores. Extensive structural and dynamical properties of the confined fluids, including hydrogen-bonding behavior, were investigated: The effects of pore width and mixture composition on the confined behavior were illustrated. It is observed that a layered structure is formed within the confined spaces and the ethanol water mixtures show segregation at larger pores, with ethanol molecules preferentially adsorbing on graphene surfaces. This microphase demixing behavior stems from the competitive effect of the solid fluid and fluid fluid interactions. Moreover, miscellaneous diffusion mechanisms have been revealed for the hydrogen-bonding mixtures within the graphene pores. In the mixtures, water and ethanol generally display analogous diffusion mechanism due to ethanol water association, converting from short-time subdiffusion to long-time Fickian diffusion in the larger nanopores. In the smaller pore (7 angstrom), both ethanol and water show a suppressed single-file diffusion behavior at the initial time and then display subdiffusion or single-file diffusion behavior. The complex diffusion behavior of ethanol water mixtures can be described by the collaborating effects of pore confinement and enhanced interaction in the hydrogen-bonding mixtures.