Atomic insights into melting behaviours of phase change material confined in nanospace

Abstract

In this study, a molecular dynamics simulation was performed to provide atomic insights into the melting behaviours of phase change materials confined in nanospace. NaCl was used as the phase change material while SiC act as the porous matrix. Both static and dynamic behaviours of atoms were analysed. The morphology evolution was illustrated and the local structure was depicted. At the low temperature, nanoconfined NaCl remains the cubic crystal structure although some atoms slightly deviate from the lattice point. After melting, the system becomes disordered and the regular crystal structure disappears. The morphology evolution is consistent with the change in the micro-structure. After melting, the main distance between cations and anions becomes shorter and the coordination number in the short range is larger than that before melting. Atomic motion is characterised using the Lindemann index. At the solid and liquid states, the increase in the Lindemann index is slow while near the phase transition point, the increase is dramatic. Compared to the bulk NaCl, the balance position more approaches the central ion. Finally, the nanoconfinement effect on melting point and latent heat, two critical thermodynamic properties for phase change materials, is discussed. The depressed melting point and latent heat are attributed to the coulombic interaction and the micro-structure difference respectively. This study aims to provide atomic insights into the melting behaviours of nanoconfined phase change materials.