Encapsulation of octadecane in poly(divinylbenzene-co-methyl methacrylate) using phase inversion emulsification for droplet generation

Octadecane (OD), a heat storage material, was encapsulated into poly(divinylbenzene-co-methyl methacrylate) or P(DVB-co-MMA) matrix via the microsuspension polymerization. The oil droplets were first generated by using the phase inversion emulsification, i.e., adding a sodium dodecyl sulphate (SDS) aqueous solution into an oil phase (monomers:OD = 1:1) containing various concentrations of poly(vinyl alcohol) (PVA). Results showed that 0.1 wt% of SDS in aqueous medium with the additional rate of 2 mL/min and 3 wt% of PVA in oil phase were the optimal conditions for the formation of nonspherical microcapsules. The smallest number- (d_n) and weight- (d_w) average diameters of P(DVB-co-MMA)/OD were, respectively, 3.1 and 3.2 µm with a narrow particle size distribution (d_w/d_n) of 1.02. The latent heats of the encapsulated OD increased with increasing MMA content of microcapsules. The heat of melting (ΔH_m; 223 J/g-OD) and crystallization (ΔH_c; 230 J/g-OD) of the OD encapsulated in microcapsules using DVB:MMA of 30:70 were higher than those using only PDVB (189 and 193 J g-OD for ΔH_m and ΔH_c, respectively) and comparable to those of bulk OD (233 and 234 J/g-OD for ΔH_m and ΔH_c, respectively). The obtained P(DVB-co-MMA)/OD microcapsules would be useful as high performance heat storage material.