Interlink between Abnormal Water Imbibition in Hydrophilic and Rapid Flow in Hydrophobic Nanochannels

Nanoscale extension and refinement of the Lucas-Washburn model is presented with a detailed analysis of recent experimental data and extensive molecular dynamics simulations to investigate rapid water flow and water imbibition within nanocapillaries. Through a comparative analysis of capillary rise in hydrophilic nanochannels, an unexpected reversal of the anticipated trend, with an abnormal peak, of imbibition length below the size of 3 nm was discovered in hydrophilic nanochannels, surprisingly sharing the same physical origin as the well-known peak observed in flow rate within hydrophobic nanochannels. The extended imbibition model is applicable across diverse spatiotemporal scales and validated against simulation results and existing experimental data for both hydrophilic and hydrophobic nanochannels.

Figure 1

Deviations in the ratio between the traditional LW equation (black dashed horizontal line) at various channel heights for both experimental and MD data of HPI NCs. The green dashed line represents the descending behavior and deviation from the classical limit (i.e., black dashed line), becoming particularly evident starting from 300 nm and extending down to around and below 10 nm. The red dashed arrow serves as a guide to the eye, emphasizing the deviation from the classical prediction below 3 nm. The arrows indicate distinct regimes. Inset: side view of the water imbibition meniscus in the MD simulation setup, represented by the black curve.

Figure 2

(a) Temporal evolution of the square of the imbibition length $x^2$. (b) Different type of driving pressures as a function of height. (c) Influence of the disjoining pressure parameter (${\pi }_{\mathrm{d}}$) on the imbibition length of water in HPI silica nanochannels.

Figure 3

The imbibition lengths for silica (a) and $h$-BN (b), determined by $x_{\mathrm{MLW}}$, vary with equilibrium contact angles within the range of 0–60 degrees for silica and 86.5–89.5 degrees for $h$-BN (indicated by color bars), respectively. Panel (c) shows the imbibition length variations for graphene with different slip lengths within the range of 10–60 nm. Experimental data obtained from various literature sources, as explained in the main text, is represented by dots. The dashed gray lines represent the results of the original LW equation. (d) The variation of enhancement factor ($\epsilon =(x_{\mathrm{MLW}}/x_{\mathrm{LW}})$) with the channel height.