Synthesis and characterization of mixed alkanes microcapsules with phase change temperature below ice point for cryogenic thermal energy storage

Highlights: • MEPCMs with C12-C14 binary alkanes as core materials were successfully synthesized. • Emulsifier concentration and HLB value have significant impact on MEPCMs synthesis. • Enthalpy and encapsulation efficiency are increasing with the increase of core/shell ratio. • Supercooling degree of MEPCMs is increasing by increasing emulsifier concentration. • MEPCMs presented good thermal durability and excellent cycling characteristics. -- Abstract: The purpose of this study was to synthesize microencapsulated phase change materials (MEPCMs) with C₁₂-C₁₄ binary alkanes as phase change materials (PCMs) and melamine-formaldehyde resins (MF resins) as shell materials by in-situ polymerization. SDS, Span80 and Tween80 were used as the compound emulsifiers. The effects of emulsifier concentrations, core/shell ratio and compound emulsifier Hydrophilic Lipophilic Balance (HLB) value on the performance of MEPCMs were investigated. The morphology, chemical structure, thermodynamic properties and thermal stability of MEPCMs were determined by SEM, FT-IR, DSC and TGA. Results show that the emulsifier concentration and HLB value have significant impact on the MEPCMs synthesis. The emulsifier concentration of 8 wt%, HLB value of 12.15 are recommended to obtain the MEPCMs with smoother and more regular morphologies. Generally, the enthalpy and encapsulation efficiency are increasing with the increase of core/shell ratio, and the supercooling degree of MEPCMs increases by increasing the emulsifier concentration. The synthesized MEPCMs present good thermal durability and excellent cycling characteristics during the 100 thermal cycles. Moreover, they also have an appreciable thermal stability and can withstand temperatures no higher than 315 °C.