Hydrogen-bond dynamics of water in a quasi-two-dimensional hydrophobic nanopore slit.

We perform molecular dynamics simulations to investigate hydrogen-bond dynamics of the TIP5P (transferable intermolecular potential with five points) model of water confined in a quasi-two-dimensional hydrophobic nanopore slit. We find that even if the average number and the lifetime of hydrogen bonds are affected by nanoconfinement, the characteristics of hydrogen-bond dynamics in hydrophobic confined water are the same as in bulk water-such as an Arrhenius temperature dependence of average hydrogen-bond lifetime and a nonexponential behavior of lifetime distributions at short time scales. The different physical properties of water in hydrophobic confinement compared to bulk water-such as approximately 40 K temperature shift-may be primarily due to the reduction of the lifetime of hydrogen bonds in confined environments. We also find that the hydrogen-bond autocorrelation function exhibits a power-law tail following a stretched exponential behavior. The relaxation time of hydrogen bonds in confined water is smaller than in bulk water. Further, we find that the temperature dependence of the relaxation time follows a power-law behavior, and the exponents for bulk and confined water are similar to each other.