Preparation of poly(divinylbenzene) microencapsulated octadecane by microsuspension polymerization: oil droplets generated by phase inversion emulsification

Poly(divinylbenzene) (PDVB) microencapsulated octadecane (OD) (PDVB/OD) for use as a heat storage material was prepared by the microsuspension polymerization of DVB/OD droplets, first generated by phase inversion emulsification (PIE). The influence of the surfactant on the colloidal stability, particle size and particle size distribution (PSD) was investigated. Capsules with a size of approximately 1.5 mu m, a narrow PSD, and good colloidal stability throughout the polymerization were obtained using polyvinyl alcohol and sodium dodecyl sulfate as the surfactant and cosurfactant, respectively, in the process of PIE. The optical and scanning electron micrographs showed that the microcapsules have a spherical shape and display a dented surface. The thermal properties and thermal stability of the PDVB/OD microcapsules were determined using a differential scanning calorimeter (DSC) and thermogravimetric analyzer, respectively. From the DSC analysis, the onset melting temperature (T-m) of the encapsulated OD (22.6 degrees C) was slightly lower than that of the bulk OD (28.7 degrees C), while it was significantly different in the case of the crystallization temperature (T-c, 12.4 degrees C and 26.3 degrees C for encapsulated and bulk OD, respectively). The latent heats of melting (H-m, 192 J g(-1)-OD) and crystallization (H-c, 195 J g(-1)-OD) of the encapsulated OD were close to those of the bulk OD (215 and 220 J g(-1), respectively).