Synthesis and Optimization of GO/PMMA/n-Octadecane Phase Change Nanocapsules Using Response Surface Methodology

Nano Encapsulated Phase Change Materials (NEPCMs) are a crucial part of solar energy systems due to their high thermal storage density. The particle size of the NEPCMs is especially of great importance due to its effect on heat transfer and long-term use during applications. In this study, nanocapsules containing Phase Change Material (PCM) n-dodecanol as core and polymethyl methacrylate (PMMA) as shell were synthesized by miniemulsion polymerization with Graphene Oxide (GO) nanosheets as an extra protective screen situated at the interface between the core and the shell. The experiments were designed with the Central Composite Design (CCD) of Response Surface Methodology (RSM). The nanocapsules synthesis experiments were conducted as per the statistical design to determine the optimum process conditions. The effect of initiator/Methyl methacrylate(MMA) mass ratio (BPO/MMA wt.%), n-octadecane/MMA mass ratio (PCM/MMA), stabilizer/MMA mass ratio (triton X-100/MMA wt.%), water/MMA mass ratio (H2O/MMA) and GO/MMA ratio on the nanocapsule properties were investigated. The correlation between nanocapsule properties (melting latent heat and average particle size of nanocapsules) and affecting factors were evaluated and verified. The numerical optimization showed that the optimum nanoparticle size (110 nm) and latent heat (148.5 J/kg) can be obtained at H2O/MMA of 11.3 wt%, PCM/MMA mass ratio of 1.88wt%, X-100/MMA of 10.81wt.%, and BPO/MMA of 2.96 wt.% and GO/MMAof 3.79wt%.  The optimized nanocapsules were characterized by Fourier Transform InfraRed (FT-IR) spectroscopy, Transmission Electron Microscope (TEM), Differential Scanning Calorimetry (DSC), ThermoGravimetric Analysis (TGA), and laser particle diameter analyzer. The thermal cycling tests indicate the high thermal resistance of the prepared core-shell system, even after 100 heating/cooling cycles, and have an excellent potential for energy storage and release performance of the system.