Polymethyl methacrylate based phase change microencapsulation for solar energy storage with silicon nitride

Silicon nitride was applied to enhance the thermal performance and mechanical properties of phase change microencapsulation (PCM) based on polymethyl methacrylate (PMMA) shell and n-octadecane core. 'A molecular bridge' was constructed to modify the surface of silicon nitride and to eliminate boundary layer between inorganic silicon nitride particle and organic PMMA shell. Thus, an innovative modified silicon nitride phase change microencapsulation (MPCM) with which silicon nitride uniformly disperses in PMMA as shell and n-octadecane as core was successfully prepared. The microencapsulation was characterized using Fourier transformed infrared spectrophotometer (FTIR), field emission scanning electron microscope (FESEM), differential scanning calorimeter (DSC) and thermal gravimetric analyzer (TGA). A micro/nano-hardness tester was also employed, in order to investigate mechanical performance of shell. The result shows that the MPCM containing 66.4% n-octadecane has 121.11 J/g latent heats of melting and 122.01 J/g latent heats of crystallization with the modified silicon nitride percentage up to 10 wt.%. The modified silicon nitride could not only enhance thermal performance, but also improve mechanical strength up to 16.24 mN which is 4 times higher than that of PCM. Additionally, wrinkles on the surface of MPCM improved special surface area as well as adaptation of volume changes during phase change process. The prepared MPCM is expected to exhibit better performance in solar energy storage technology.