Improvement of the thermostability of silicone oil/polystyrene microcapsules by embedding TiO2/Si3N4 nanocomposites as outer shell

TiO2 and Si3N4 nanoparticles (nano-TiO2/Si3N4) were applied to enhance the thermostability of silicone oil microcapsules based on polystyrene shell using a Pickering emulsion method. The emulsion droplets consisting of silicone oil, monomers and initiator were first stabilized in an aqueous medium containing TiO2 and Si3N4 nanoparticles as surfactants. The obtained emulsion was subsequently heated and polymerized to form the silicone oil composite microcapsules embedded with nano-TiO2/Si3N4 in the polystyrene shell. Various techniques were used to characterize the as-prepared composites so as to investigate the effect of nanoparticles loading and silicone oil content on their chemical composition, morphology and thermal performance. Results showed that the composite silicone oil microcapsules present a well-defined spherical structure with a mean size of 10-20 mu m. Compared with pure silicone oil, the thermostability of the microencapsulated silicone oil is significantly enhanced at a low content of nano-TiO2/Si3N4. In particular, these microcapsules showed a considerable increase for initial decomposition temperature and maximum decomposition temperature. Such a notable increment is attributed to the existence of compact PS/TiO2/Si3N4 hybrid shell on the silicone oil droplets surface giving silicone oil core a protective effect.