Charged clay surfaces can impact the storage and mobility of hydrocarbon and water mixtures. Here, we use equilibrium molecular dynamics (MD) and nonequilibrium MD simulations to investigate hydrocarbon-water mixtures and their transport in slit-shaped illite nanopores. We construct two illite pore models with different surface chemistries: potassium-hydroxyl (PH) and hydroxyl-hydroxyl (HH) structures. In HH nanopore, we observe water adsorption on the clay surfaces. In PH nanopores, however, we observe the formation of water bridges because of the existence of a local, long-range electric field. Our NEMD simulations demonstrate that the velocity profiles across the pore depends strongly on water concentration, pore width and the presence or absence of the water bridge. This fundamental study provides a theoretical basis for understanding nanofluidics with charged surfaces and can be applied in such as biological processes, chemical and physical fields, and the oil and gas extraction in clay-rich formations.

Charged clay surfaces can impact storage and mobility of hydrocarbon and water mixtures. Here, we use equilibrium molecular dynamics (MD) and nonequilibrium MD simulations to investigate hydrocarbon-water mixtures and their transport in slit-shaped illite nanopores. We construct two illite pore models with different surface chemistries: potassium-hydroxyl (P-H) and hydroxyl-hydroxyl (H-H) structures. In H-H nanopore, we observe water adsorption on the clay surfaces. In P-H nanopores, however, we observe the formation of water bridges or columns between the top and bottom pore surfaces. This is because of the existence of a local, long-range electric field within the P-H pore causing water molecules to align in a specific direction promoting the formation of a water bridge. Our NEMD simulations demonstrate that the velocity profiles across the pore depends strongly on the presence or absence of the water bridge. This study provides a theoretical basis for understanding of nanofluidics with charged surfaces.