Direct and reverse desymmetrization process in O/W Pickering emulsions to produce hollow graphene oxide Janus micro/nano-particles

Abstract

In this study, hollow graphene oxide Janus (HGOJ) micro/nano-particles were synthesized using direct and reverse desymmetrization processes. Different size hollow graphene oxide particles, as the base, were produced using the method proposed by Cao et al. Both direct and reverse desymmetrization processes were performed in O/W Pickering emulsions using melted paraffin as the oil phase. This provided a significantly high oil/water interface at which the Janus characteristic was tailored onto the surface of micro/nano stabilizing particles, via the surface modification process. In the direct desymmetrization process, the hydrophilic nanoparticle spontaneously migrated from the water phase toward the oil/water interface while it was the migration of hydrophobic microparticles from the oil phase toward the oil/water interface which was responsible for the stabilization of oil droplets. Accordingly, the type of the desymmetrization process directly affected the value of the three-phase contact angle (β) as the main determinative parameter in the formation of hollow graphene Janus micro/nano-particles. The amphiphilic property of the synthesized HGOJ micro/nano-particles was evaluated in water/chloroform and PS/PMMA mixtures where acceptable results were obtained. It was proved that the hydrophobic stabilizing particles can be also turned into Janus particles via reverse desymmetrization process, in O/W Pickering emulsions, since regardless of the parameter β, the size of stabilizing particles and their hydrophilicity/hydrophobicity both obtained Janus micro and nanoparticles were capable of controlling the interface. FE-SEM, light-microscopy, FTIR, EDX, TGA and contact angle tests were used to evaluate the performance of the different stages of the synthesis process.