Sodium acetate trihydrate (SAT) is a promising phase change material for thermal energy storage through phase transition, yet its microscopic mechanisms of phase transition, especially melting and intrinsic supercooling, remain unclear. In this study, all-atom molecular-dynamics simulations were performed to elucidate the melting pathway, supercooling mechanism, and facet-dependent stability of SAT. The analysis of melting dynamics reveals a three-stage transition comprising interfacial relaxation, melting-front propagation, and liquid stabilization. Melting is driven by the breakdown of long-range ionic order and the reorganization of water molecules into a bulk hydrogen-bonded network, where ${\mathrm{H}}_2\mathrm{O}\text{−}{\mathrm{H}}_2\mathrm{O}$ interactions transform from repulsive to attractive. Under isothermal conditions, liquid SAT remains metastable down to 220 K without crystallization during 1000 ns. The energetic decomposition reveals a dual stabilization mechanism: (i) electrostatic trapping arising from strengthened $\mathrm{N}{\mathrm{a}}^{+}\text{−}\mathrm{C}{\mathrm{H}}_3\mathrm{CO}{\mathrm{O}}^{-}$ pairing and enhanced short-range charge correlations, and (ii) ion-water cooperative stabilization that locks hydration shells and slows the reorientation of water molecules. These effects produce a polarized yet dynamically constrained liquid network, in which the number of hydrogen bonds increases while their collective electrostatic coherence weakens. Comparative simulations of the (402), (–402), and (062) crystal planes further reveal distinct interfacial energetics and hydrogen-bond organizations, with the (402) facet exhibiting the strongest interfacial stability and the (062) facet showing diffuse hydration and weak lattice cohesion.

Close

PrevNext

View figure in article

• Classical statistical mechanics
• Phase transitions
• Crystal structures
• Inorganic compounds
• Liquid-solid interfaces
• Supercooled liquid
• Molecular dynamics