Density-dependent phase transition in nano-confinement water using molecular dynamics simulation

Water molecules with different densities confined between two parallel surfaces of graphene, graphite, boron nitride (BN) and silicon carbide (SiC) have been simulated at 300 K. Different thermodynamics, structural, and dynamical properties have been investigated using the SPC/E model for the confined water molecules. Our results showed that the water molecules confined between the graphite surfaces have lower energies and thus, they are more stable than the other systems. The confined water molecules tend to form square and rhombus structures at higher densities and they tend to form pentagonal and hexagonal structures at lower densities. The most stable state (the case of graphite at ρ = 0.4 (g/cm3)) consists of a mixture of all structures with more square and rhombus structures. The confined water molecules also tend to lie at the center of the surface hexagonal rings by increasing the density. The different results indicated that a phase transition has been happened in the confined systems by increasing the density. In order to investigate this phenomenon, we have calculated the water-water energies, average number of the hydrogen bonds (HBs), and translational order parameter for the different systems.