Fig. 3.

Instantaneous interfaces encompassing dewetted regions (shown in purple) between the hydrophobic surfaces (shown in cyan) separated by $d=20$ Å highlight the presence of (A) a vapor tube for $N=N_{\text{kink}}-12$, and (B) an isolated cavity for $N=N_{\text{kink}}+3$. Water molecules not shown for clarity. (C) Average of the binary vapor tube indicator function, $h_{\text{tube}}$, conditioned on the number of waters in confinement being N, displays a sharp transition from 1 to 0 as N is increased. The color scheme is the same as that in Fig. 2. The value of N corresponding to ${\langle h_{\text{tube}}\rangle }_N=0.5$ (dashed line) is defined as $N_{\text{tube}}$. (D) $N_{\text{tube}}$ is identical to the location of the kink in the free energy profiles, $N_{\text{kink}}$, as shown by the agreement between the simulation data and a straight line (dashed). This agreement confirms that the kink demarcates conformations with and without vapor tubes. (E) Conditional average of the isolated cavity indicator function, ${\langle h_{\text{cav}}\rangle }_N$, shows a sharp increase in the vicinity of $N_{\text{kink}}$ (the square symbols correspond to $N_{\text{tube}}$), followed by a gradual decrease at larger N values, and eventually vanishes around $N=N_{\text{liq}}$. (F) For the larger d values, ${\langle h_{\text{tube}}\rangle }_{N_{\text{tube}}}={\langle h_{\text{cav}}\rangle }_{N_{\text{tube}}}=0.5$. However, for the smaller d values, ${\langle h_{\text{cav}}\rangle }_{N_{\text{tube}}}<0.5$, suggesting the possibility of direct vapor tube nucleation without isolated cavities as intermediates.