Hydrophobic-Hydrophilic Double-Layered Shells for Paraffin-Based Heat Storage Microcapsules.

Hydrophobic-hydrophilic double-layer polymer capsules containing hexadecane (HD) were prepared by a one-pot suspension polymerization strategy for thermal energy storage. HD encapsulated with hydrophobic polymer shells often exhibits reduced latent heat and significant supercooling because the crystallization of confined paraffin (HD) is restricted by hydrophobic interaction with the inner shell interface. In the present approach, the difference in monomer reactivity ratios between conjugated and nonconjugated monomers was utilized to spontaneously form a poly(divinylbenzene) (PDVB) -rich outer shell and a vinyl acetate (VAc)- or vinyl butyrate (VBu)-rich inner layer. Subsequent hydrolysis converted the inner layer to hydrophilic poly(vinyl alcohol) (PVA). Thermal analysis revealed that HD encapsulated in PDVB capsules showed reduced latent heat and significant supercooling. In contrast, the double-layer capsules exhibited markedly improved thermal properties. The enthalpy of fusion increased to 229 J g-1-HD, which was nearly identical to that of pure HD, and the supercooling decreased to 2.2 °C. These results indicate that the hydrophilic inner layer effectively restores bulk-like phase-change behavior of confined HD. The present strategy provides a useful interfacial design approach for polymer-encapsulated phase change materials with minimal latent heat loss.