Design And Synthesis Of Magnetic Microencapsulated Phase Change Materials And Magnetic Polyimide Hybrid Films

PCMs are able to absorb and release heat from the environment during the phase change process, which can act as thermal energy storage and management materials. Microencapsultion as an efficient packaging technology is required to prevent the leakage of PCMs during their solid-liquid phase transition process.We designed a kind of magnetic microcapsules based on w-eicosane cores and Fe3O4/SiO2 hybrid shells for dual-functional PCMs in chapter two. The magnetic microcapsules were synthesized in a two-step way. At first, we prepared solid-stabilized emulsions in which Fe3O4 nanoparticles (Fe3O4 NPs) were self-assembled onto the surface of n-eicosane. Then we initiated hydrolysis and polycondensation of tetraethyl orthosilicate (TEOS) at the O/W interface to protect n-eicosane droplets coated with Fe3O4 NPs. The obtained magetic microcapsules presented perfect spherical shape and core-shell structure. The chemical compositions of magnetic microcapsules from the surface to the center were SiO2, Fe3O4 NPs and n-eicosane. Fe3O4 domains presented inverse spinel structure and SiO2 matrix was amorphous. In addition, these Fe3O4 domains were superparamagnetic. These magnetic microcapsules achieved excellent heat storage capacity, good thermal reliability and high thermal stability because of the compact Fe3O4/SiO2 hybrid shells. Due to the dual-functional feature, the magnetic capsules can be used in the fields of intelligent fibers or textiles with temperature regulation and anti radiation functions, the stealth products with electromagnetic-infrared double shielding capability, the anti-jamming coatings of integrated circuit chips, etc.In chapter three, we designed a kind of magnetic polyimide (PI) hybrid films that can function as thermal energy management and electromagnetic shielding materials. Firstly, magnetic microcapsules based on PEG/Fe3O4 hybrid cores and organosilica shells were prepared. During the synthesis of the magnetic microcapsules, W/O emulsions were fabricated in advance and then the organosilica shells were coated onto the the surface of the PEG/Fe3O4 hybrid cores through interfacial polycondensation. Then poly(amic acid) (PAA) was mixed with the magnetic microcapsules and was casted on a glass plate to obtain composite films. The composite films were heated to gain the magnetic PI hybrid films. The magnetic microcapsules exhibited a cup-shaped morphology with core-shell structure and Fe3O4NPs were dispersed in PEG cores. The magnetic microcapsules and the PI hybrid films have good thermal energy management and thermal stability capacity. Last but not the least, the novel magnetic PI hybrid films presented both good dielectric loss properties and shielding performance and can be used to fabricate electronic equipments and components.