The nano-encapsulated and nanoparticle-enhanced phase change materials (PCM) which can be used for thermal energy storage have attracted much attention in recent years. To understand the heat and mass transfer mechanisms of the nano-encapsulated and nanoparticle-enhanced PCM on the molecular and atomic scale, the molecular dynamics (MD) simulations were performed in the present paper. The nano-encapsulated PCM with different shell thicknesses were fabricated by using n-octadecane as core material and SiO2 as shell material. The nanoparticle-enhanced PCM were formulated by mixing Al nanoparticles into n-nonadecane. The n-nonadecane, n-eicosane, n-heneicosane and n-docosane were used to build the pure PCM models as unencapsulated PCM systems for comparison. The results showed that the torsion and extension of the core material molecule chains could be restricted by excessive thick shell in the nano-encapsulated PCM systems. The mobility of the nanoparticle-enhanced PCM decreased with the increase of the diameter of added nanoparticles. Both excessive thick and thin shells were disadvantageous for encapsulated PCM. And the appropriate size of particle was very important for heat transfer enhancement of the nanoparticle-enhanced PCM. The MD simulations proposed herein can be helpful for the material design and performance optimization of thermal energy storage and transport PCM. (C) 2013 Elsevier Ltd. All rights reserved.