High temperature behavior of water inside flat graphite nanochannels

By means of molecular dynamics calculations performed at high temperatures, we were able to calculate the phase diagram of liquid water confined inside narrow graphite channels. We found stable liquid phases all the way to $398\mathrm{K}$, failing to reach the critical temperature for all of the systems under consideration. We also analyzed how the temperature variations in the range of 298 to $398\mathrm{K}$ affected the hydrogen bond network and found that the main variation in the infrared spectra of confined water at high temperatures was the forward shifting of the bending peak.

Figure 1

Phase diagram for the system with $9\mathrm{\AA }$ of interplate separation. Dotted lines are guides to the eye, the crosses with the error bars being the results of our simulations.

Figure 2

Same as in Fig. 1 but for a separation $12\mathrm{\AA }$.

Figure 3

Same as in previous figures for a slab width of $15\mathrm{\AA }$.

Figure 4

Oxygen density in $\mathrm{g}∕{\mathrm{cm}}^3$ versus the $z$ coordinate for separations 15 (full line), 12 (dashed line) and $9\mathrm{\AA }$ (dotted line). All the data are given at $398\mathrm{K}$.

Figure 5

Average number of hydrogen bonds for the three systems considered: 15 (full circles), 12 (open squares), $9\mathrm{\AA }$ (full squares). Dotted lines are guides to the eye. The destruction rate is shown to depend on the graphite separation.

Figure 6

Spectral densities obtained from our simulations at $T=398\mathrm{K}$. The curves have been displaced vertically for the sake of clarity. From bottom to top, we have bulk water density of $1\mathrm{g}∕{\mathrm{cm}}^3$, and confined water between two graphite layers separated by 9, 12, and $15\mathrm{\AA }$. One observes that the bending peaks are moved forward while the stretching bands are basically unchanged with respect to bulk values.