Preparation and characterization of PMMA/TiO2 hybrid shell microencapsulated PCMs for thermal energy storage

Abstract

A novel n-octadecane@PMMA/TiO2 hybrid shell PCM was prepared through a facile emulsion method, then characterized and estimated for thermal energy storage. During the synthetic process, the emulsion was enhanced by modified TiO2 particles to improve the stability and thermal conduction. The aggregation process can be performed by an eco-friendly and efficient way, which was carried out under ultraviolet radiation for 10 min at 35 °C. The prepared microencapsulated PCMs have excellent nuclear shell structure, and the surface of the shell covered with TiO2 particles uniformly. The TGA and DSC analysis showed that the microencapsulated PCMs have excellent thermal stability, high enthalpy and small degree of supercooling, which were suitable for thermal energy release and retrieval. The encapsulation efficiency of the microcapsules reached 67.2% when the appropriate proportion of MMA/n-octadecane was 1:1, and the melting enthalpy was 179.9 J/g. We also studied the crystallization behavior by in situ XRD method, the results showed that the crystallization behavior was different comparing with the bulk n-octadecane and hybrid shell PCMs. During the crystallization process, surface crystallization phenomenon occurred on the interface, which existed between inner surface of the microcapsules and melted n-octadecane. Subsequently, two sequential exothermic peaks were formed, which was different with bulk n-octadecane (only one exothermic peaks). The work was not only to develop a method to prepare the organic-inorganic hybrid shell Micro-PCMs, but also to study the discipline of crystallization behavior between the bulk n-octadecane and hybrid shell PCMs.