Study Of Myristic Acid/Silica Phase Change Nanocapsules And Their Heat Storage Fluids

Phase change nanocapsules,containing myristic acid?MA?as core and silica?SiO₂?as shell,were synthesized for the first time via the sol-gel method.The influences of the dosages of two surfactants?PVP and PVA?,pH value,the mass ratio of myristic acid to tetraethoxysilane?TEOS?on the structure and thermal property of the prepared samples were studied.The characterizations revealed that all the synthesized samples have uniform and spherical core-shell structure,and the micro-morphology of the synthesized nanocapsules was satisfactory when the mixed surfactants were used and the pH value was at 11.The mean thickness of the shell of the samples increased with the decrease of the mass ratio of the MA/TEOS.The melting/solidifying enthalpy and encapsulation ratio of the nanocapsules can reach 164.8 J/g,168.9 J/g and 81.38%,respectively.The nanocapsules have good thermal properties.Carbon coated Cu nanoparticles?Cu@C?was prepared with a two-step synthetic method.The effects of the parameters of the types of surfactants,Cu²⁺concentration and reaction temperature on the morphology of the prepared Cu nanoparticles,and the effects of glucose dosage and heat treatment temperature on the structure of Cu@C nanoparticles were investigated,respectively.It was found that the Cu hexagonal nano-flakes with narrow size distribution and good dispersibility can be obtained with the use of Arabia gum as the surfactant.The increase of the reaction temperature and Cu²⁺concentration could lead to the decrease of the size of Cu nanoparticles.When the mass ratio of Cu particles to glucose was 1:8,the synthesized Cu@C nanoparticles can have perfect core-shell structure.Finally,MA@SiO₂ nanocapsule suspensions and water based MA@SiO₂/Cu@C composite fluids were prepared,respectively.The effects of the mass fraction Arabia gum and Cu@C nanoparticles on the suspension stability,viscosity and thermal performance of the fluid were studied.It was found that the water based MA@SiO₂/Cu@C composite fluid has good suspension stability,viscosity,thermal conductivity and heat storage performance.