Surface wettability and capillary flow of water in nanoslits of two-dimensional hexagonal-boron nitride

The wettability and imbibition dynamics of water within 2-dimensional hexagonal boron nitride (h-BN) nanochannels were investigated through nanoscale molecular dynamics simulations. Results from the sessile drop and liquid plug methods indicate that the contact angle on h-BN is notably lower than that on graphene, with single-layer h-BN exhibiting greater hydrophobicity compared to multilayer h-BN. The disjoining pressure in liquid nanoplug was calculated to validate the Young-Laplace equation. During the imbibition process, the penetration length follows l² = S_lt. Simultaneously, the decrease in internal energy (ΔE) follows ΔE = −S_Et^1/2. While the Lucas-Washburn expression (l² ∼ wt) can capture such behavior, it does not account for the dependence on channel width (w), where w = Nb, with N denoting the number of h-BN sheets and b the thickness. In wide nanoslits (N > 4), the penetration velocity decreases as the channel width increases. The final ΔE converge to the same value, and S_E²/S_l remains constant. In narrow nanoslits (N ≤ 4), the penetration velocity does not decrease consistently with channel width. The final ΔE does not converge to a consistent value for N = 1, 1.5, and 2, and S_E exhibits distinct trends with S_l. Comparisons reveal that water in h-BN nanochannels exhibits a notably higher imbibition velocity than in graphene due to differences in the driving force.