Fig. 11 Water and hydrocarbon velocity profiles at the acceleration and water concentration of 0.002 nm/ps2and 71.43% respectively in different PH nanopore sizes. The result indicates that pore size impacts the velocity patterns. At 5nm, we observe a parabolic shape for the flow profiles which get progressively flatter as the pore size increases.
In Fig. 12, we take a closer look at the water bridges present in the PH pores at a water concentration of 71.43. Hydrocarbon molecules are not shown for clarity. The red-colored water molecules are those adjacent to the pore surface and the yellow-colored water molecules are those present in the water bridge. Fig. 12a shows the distribution of water in a 5nm PH pore obtained from our equilibrium MD (EMD simulations) on top and under 0.002 nm/ps2 on the bottom. The water bridge in Fig. 12a is a sheet extending across the entire x-direction in the 5nm PH nanopore.
Figs. 12b-c show the corresponding information for 10nm and 15nm pore widths. Water molecules move freely between the water bridge and adsorbed layer resulting in the velocity profile in Fig. 12a (shown in a blue line). However, when pore sizes increase to 10 nm or 15 nm, there is limited or no exchange of water molecules between the film and the bridge. The combination of a constant acceleration and no exchange contributes to the flat velocity profiles observed in Figs. 12b-c.