Water confined in hydrophobic environments

This thesis applies statistical physics approaches and computer simulation methods to investigate the dynamical properties and phase transitions of water confined in hydrophobic environments.;A diffusion anomaly, an increase of diffusion upon compression, is one of many unexpected behaviors observed in water. To calculate the diffusion coefficient of confined water in the confining direction, we use the concept of the continuous random walk. We find that a diffusion anomaly of water is absent in the direction perpendicular to the confining walls down to 220 K, whereas there is a diffusion anomaly, similar to that in bulk water, in the direction parallel to the walls.;Anomalous behaviors of water compared to simple liquids are generally ascribed to a hydrogen bond. From investigations of confinement effects on a hydrogen bond, 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. The different physical properties of water in hydrophobic confinement compared to bulk water---such as ∼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 characterized by an exponent which depends on the system dimensionality.;Vapor and liquid may transform into each other either discontinuously by crossing a first-order transition line or continuously without crossing a transition line, indicating an existence of the vapor-liquid critical point. In contrast to the phase transition line between vapor and liquid, the first-order transition line between solid and liquid is believed to persist indefinitely without terminating at a critical point. We show that either a first-order transition or a continuous transition between solid and liquid can occur for water confined in a quasi-two-dimensional hydrophobic nanopore slit. This finding indicates that the connection point between first-order and continuous transition lines might be a solid-liquid critical point with a tricritical nature.