Fig. 12 Molecular distribution and velocity profiles of water
in PH pores of different widths at a water concentration of 71.43%. The
acceleration is 0.002 nm/ps2. Hydrocarbon is not shown
for clarity. The red dots represent adsorbed water and the yellow dots
are those in the water bridge. In a 5 nm PH nanopore, acceleration
causes the adsorbed layer to exchange both mass and velocity with water
at the pore center. Increasing the pore size to 10 nm or 15 nm, as
revealed by the flatter velocity profile, no mass or velocity exchange
occurs between the adsorbed layer and water in the bridge or pore
center.
Effect of Water Concentration
Fig.13 shows the water (Fig.13a) and hydrocarbon (Fig.13b) velocity
profiles at 0.002 nm/ps2 in a 10 nm PH nanopore for
different values of water concentration. The velocity of water decreases
with increasing water concentration (Fig. 13a) because of the increased
thickness of the water bridge. The
thickness of the water bridge at water concentrations of 18.87%,
58.82%, 71.43% and 80.00% is 0.94 nm, 1.24 nm, 1.60 nm and 1.96 nm
respectively. This is shown in Fig. S9 in Supporting Information.
Fig. 13b shows an increased hydrocarbon velocity for an initial increase
in the water concentration which has been attributed to the creation of
smoother surfaces for hydrocarbon flow69. However,
when the water concentration is increased, the width of the water bridge
progressively increases (shown in Fig S10), thereby hampering
hydrocarbon flow.
Fig. 13 also indicates flat velocity profiles exist for both the oil and
water phases. Because of the hydrophilic surface, hydrocarbon molecules
are responding to the acceleration and are not strongly influenced by
the pore surfaces, leading to a flatter velocity profile.