Core double-shell cobalt/graphene/polystyrene magnetic nanocomposites synthesized by in situ sonochemical polymerization

Core double-shell cobalt/graphene//polystyrene nanocomposites (Co/C//PS) were synthesized by an in situ sonochemical polymerization technique. Commercial Co/C nanoparticles are used and successfully lead to gram-scale production of processable nanocomposite. Synthesized Co/C//PS nanocomposites result in homogeneous and dense dispersion of particles with or without additional polymeric matrix. They showed improved thermal properties such as higher initial degradation temperatures and a significant increase of glass transition temperature (i.e. 10 to 12 degrees C) in contrast to neat PS. These results suggest that covalent bonding occurs between PS and the graphene shell, and may be promoted by two surface reactions: grafting from when the monomer is pre-immobilized on graphene and grows to polymer, and grafting to when pre-synthesized polymer is immobilized on graphene. Both mechanisms are compared and explained. HR-TEM observations revealed polymer shells of 4 to 5 nm covering Co/C nanoparticles or at least small aggregates. However, the number of layers of the graphene shell which consists of 6 to 8 regular layers on raw particles decreases to 3, this layer reduction can be explained by a partial amorphization of graphene occurring during the polymerization. Nevertheless, Co particles are still efficiently protected from oxidation as final Co/C//PS nanocomposites are able to sustain high mass-magnetization (i.e. similar to 49 emu g(-1) for 94% wt Co/C). First indications of satisfying mechanical cohesion are also shown by the formation of two relevant nanocomposite shapes (film and disk). In conclusion, in situ polymerization is a powerful synthesis method to produce processable high-magnetization nanocomposites.