Surface Phase Transition in Anomalous Fluid in Nanoconfinement

We explore by molecular dynamic simulations the thermodynamical behavior of an anomalous fluid confined inside rigid and flexible nanopores. The fluid is modeled by a two length scale potential. In the bulk, this system exhibits the density and diffusion anomalous behavior observed in liquid water. We show that the anomalous fluid confined inside rigid and flexible nanopores forms layers. As the volume of the nanopore is decreased the rigid surface exhibits three consecutive first-order phase transitions associated with the change in the number of layers. These phase transitions are not present for flexible confinement. Our results indicate that the nature of confinement is relevant for the properties of the confined liquid, which suggests that confinement in carbon nanotubes should be quite different from confinement in biological channels.