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 mu m. 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 similar to 9 degrees C is observed in the cooling process for the MicroC18 with single PMMA shell (MicroC18(0)). MicroC18 with comb-like copolymer shells have lower onset and peak melting temperature than that of MicroC18(0). Supercooling of MicroC18 is not effectively suppressed until the molar ratio of ODMA reaches 0.3. A hypothesis to explain this behavior is presented.