Preparation of reduced graphene oxide modified magnetic phase change microcapsules and their application in direct absorption solar collector

Development of latent functionally thermal fluid (LFTF) with excellent optical absorption and controllable heat transfer properties for direct absorption solar collector (DASC) is crucial in solar thermal utilization. In this study, the microcapsule, with melamine-formaldehyde (MF) resin shell and octadecane core, was prepared via in situ polymerization, as its shell was modified by reduced graphene oxide (rGO) and its core was doped with oleic acid coated Fe3O4 magnetic nanoparticles (OA-MNs). The microstructure, optical, thermal and magnetic properties of rGO modified magnetic phase change microcapsules (rGO-MPCMs) were investigated by means of various characterizations. The experimental results revealed that adding rGO substantially enhanced the thermal conductivity of magnetic phase change microcapsules (MPCMs) and only had tiny impact on the phase change behavior of MPCMs. Meanwhile, the thermal stability of octadecane in rGO-MPCMs was remarkably improved due to MF resin shell served as protective barrier. Furthermore, the rGO-MPCMs slurry exhibited better optical absorption and thermal storage capacities compared with MPCMs slurry and deionized water, thus enhancing photo-thermal conversion performance. Under an external magnetic field, the rGO-MPCMs in slurry presented excellent controllability and recyclability. Our research demonstrated that the rGO-MPCMs slurry, as a desirable working fluid, showed spacious application prospect for DASC.