The Preparation Of Polymeric Nanocapsules Of Phase Change Materials

Miniemulsion polymerization was investigated in terms of a novel niuioencapsulation technique. The investigation shows that miniemulsion polymerization is very promising to prepare nanocapsules. Nanocapsules containing phase change materials (paraffin and alkanes) were successfully prepared by one-step miniemulsion polymerization. The size of the capsule is around 100nm. The morphology of the latex particles was greatly influenced by thermodynamic factors (the level and type of surfactant, the level of hydrophilic monomer, and monomer/paraffin ratio), kinetic factors (the level of crosslmker and chain transfer agent) and nucleation modes.A small amount of hydrophilic co-monomer (lwt%) was found to facilitate the formation of core-shell structure, however a larger amount of the co-monomer was detrimental. The amount of surfactant was found to have an optimal value: less of it cannot stabilize the system of emulsion, but more of it favors the form of half-moon structure. The composite surfactant of SLS/OP-10 benefits the form of capsule structure. At lower St/paraffin ratio, it is increasingly more difficult to attain the perfect encapsulation. The addition of the crosslinking agent was found to hinder the good phase-separation of polymer and paraffin while the chain transfer agent played a promoting role in the phase-separation. Homogeneous nucleation is detrimental to the encapsulation and must be suppressed.In the case of MMA as a main monomer, the optimal conditions for a good encapsulation are: SDS(1.0wt%), hydrophilic comonomer (1.0wt% MAA).In the case of St, the optimal conditions are: SDS (1.0 wt%), hydrophilic comonomer (1.0wt% MAA), chain transfer agent (0.2wt% DDT).Under the optimal conditions, little difference of the structure of capsules were observed when an oil-soluble initiator (AIBN) replaced KPS. As the solid content of the latex was increased from 20% to 40%, the morphology of latex particles was littlechanged.In addition, it was found that as phase change material is encapsulated in nanocapsules, crystallization and melting behaviors of PCM show pronounced nano-size-dependent effects. The heating/cooling cycle experiments indicated that the prepared nanocapsules are strong enough to resist stress caused by the change of volume causing by the phase change.