Fabrication, Characterization and Suppression of Supercooling in Microencapsulated n-Octadecane with Methyl Methacrylate-Octadecyl Methacrylate Copolymer as Shell

Supercooling remains a key issue for the potential application of microencapsulated phase change materials (MicroPCMs). The aim of this study is to investigate the effects of the composition of a shell on the suppression of supercooling for MicroPCMs. Microcapsules containing n-octadecane (MicroC18) with various compositions of methyl methacrylate (MMA)-octadecyl methacrylate (ODMA) copolymer as shells were fabricated through suspension-like polymerization. Field-emission scanning electron microscopy (FE-SEM) micrographs show that a series of microcapsules with spherical shapes were formed. The average diameter of MicroC18 was in the range of 1.30–1.36 μm. Differential scanning calorimetry (DSC) results indicated that all the MicroC18 crystallizes into a stable triclinic phase via a metastable rotator phase (R _I) from the liquid phase. The occurrence of R _I phase is attributed to the lower nucleation barrier decreased by the surface freezing, which is detected by X-ray Diffraction. Supercooling of ∼9 °C is observed in the cooling process for the MicroC18 with single PMMA shell (MicroC18₀). MicroC18 with comb-like copolymer shells have lower onset and peak melting temperature than that of MicroC18₀. Supercooling of MicroC18 is not effectively suppressed until the molar ratio of ODMA reaches 0.3. A hypothesis to explain this behavior is presented.