Thermodynamics, structure, and dynamics of water confined between hydrophobic plates

Abstract

We perform molecular dynamics simulations of 512 waterlike molecules that interact via the TIP5P potential and are confined between two smooth hydrophobic plates that are separated by 1.10 nm. We find that the anomalous thermodynamic properties of water are shifted to lower temperatures relative to the bulk by approximately 40 K. The dynamics and structure of the confined water resemble bulk water at higher temperatures, consistent with the shift of thermodynamic anomalies to lower temperature. Because of this T shift, our confined water simulations (down to T=220 K) do not reach sufficiently low temperature to observe a liquid-liquid phase transition found for bulk water at T approximately 215 K using the TIP5P potential, but we see inflections in isotherms at lower temperatures presumably due to the presence of a liquid-liquid critical point. We find that the different crystalline structures that can form for two different separations of the plates, 0.7 and 1.10 nm, have no counterparts in the bulk system, and we discuss the relevance to experiments on confined water.