Fig. 4 Distribution of water (in blue) and hydrocarbon (in black) in hydroxyl-hydroxyl (HH) and potassium-hydroxyl (PH) in 5nm. Illite is not shown for clearance. The figure shows that water-bridges are prevalent in PH pore systems, while adsorption is dominant in HH.
The distribution of water in PH pores is in marked contrast to the HH nanopores. Fig. 4c shows the water-bridge phenomenon (corresponding to the peak in the number density of water shown in a blue line) at Cw of 18.87%. Increasing the Cw to 58.82% as shown in Fig.4d leads to the two water bridges demonstrated by the existence of two peaks in the water density profile. This effect has been attributed to ‘capillary condensation’76–78, but we present another argument in this paper for the existence of water bridges. If this were purely capillary condensation, the water bridge should vanish as pore width increases. However, even at 10nm and 15nm pore widths, the water bridges remain intact (See Fig.S-3 in Supporting Information).
It is important to note that the water-bridge phenomenon can also exist in an HH clay-hosted pore under specific conditions, typically at higher water concentrations and for smaller pore widths. Table 1 shows the conditions under which a water bridge occurs.
Table 1 . The matrix below shows conditions under which a water bridge will form for the models considered in this study.