Molecular dynamics study on the interaction between metal-organic frameworks and phase change core materials

Advanced phase change energy storage materials are the core and key to promoting the development of energy storage technology. As the core of phase change energy storage technology, the development of phase change materials (PCMs) has attracted more and more attention. At present, solid‒liquid PCMs are widely used. The main problem in the development of PCMs is that they are prone to liquid leakage in the process of phase change and need to be encapsulated before use. This not only increases the thermal resistance between the PCMs and heat source equipment, reducing the heat transfer efficiency, but also increases the weight of the energy storage device, which greatly limits its practical application. As a result, the development of PCMs with excellent comprehensive performance is of great significance for the field of thermal energy storage and utilization. Due to the regular channel structure and the high porosity, metal-organic frameworks (MOFs) are very suitable to serve as the PCMs carrier to realize effective packaging of phase change core materials. In this work, the structural properties of Cr-MIL-101 loaded with different core materials, namely, the octadecane, octadecanoic acid, octadecylamine, and octadecanol molecules, were investigated by molecular dynamics simulation method, which mainly considers the interaction between the phase change core and the MOFs substrate, the diffusion characteristics, and the spatial distribution characteristics of the core in the MOFs channel. The study indicates that the interaction between octadecanoic acid and MOFs substrate is the strongest, followed by the interaction between the substrate and octadecanol and octadecamine, while the interaction between the substrate and octadecane is the weakest. This result is also reflected in many aspects, such as the interaction energy between the molecules and MOFs, the radius of rotation, the molecular kinetic energy, the self-diffusion coefficient, and the heat capacity. In addition, when the interaction between the core material molecules and the interaction between MOFs and the core material reach an equilibrium, the core material molecules are in a relatively free state in the pore, which is conducive to diffusion, and then to the crystallization of the core materials.