Viscosity and Structure of Water and Ethanol within GO Nanochannels: A Molecular Simulation Study

The behavior of liquids in two-dimensional (2-D) graphene oxide (GO) nanopores is important for developing GO-based nanoscience and nanofluidics. Herein, molecular dynamics simulation was carried out to study the equilibrium structures and shear viscosity for water and ethanol confined within 2-D GO nanochannels. It was observed that both species obviously exhibit structured features near GO surfaces. The confined viscosities are anisotropic with axial shear viscosity larger than vertical viscosity. The axial shear viscosities of water and ethanol are greatly enhanced for the 2-D GO nanochannels, wherein the viscosity features a decreased pattern with the pore width. Compared with water molecules, the confinement of GO channels has more effect on the viscosity of ethanol molecules. The confined shear viscosity can be described by combining contributions of the interfacial layer viscosity and the bulk-like viscosity. The influences of oxidation degrees and pore widths on the structure and transport properties have been systematically investigated, in which the interlayer viscosity is the critical determining factor. The confined structures and surface interaction were applied to interpret the transport properties of confined liquids. The enhanced interfacial layer viscosity can be attributed to the surface hydrogen-bonding interaction arising from the oxygen-containing functional groups.