Studies On Systhesis And Properties Of High Thermal Conductivity Organic Phase Change Materials

Phase change materials (PCMs), which can be utilized in many fields such as solar energy storage, energy efficient buildings and smart textiles, have attracted more and more attention recently.Organic PCMs were extensively investigated for their advantages such as high latent heat, stable physical and chemical properties and nontoxic and non corrosive. However, low thermal conductivity of organic PCMs greatly reduced their energy storage efficient.In this research, the thermal conductivity of organic PCMs have been improved by forming a composite with metallic oxide nanoparticles and graphene, respectively, and fabrication PCMs nanocapsules. Meanwhile, intensive research has been taken on the properties of resulting composite through various testing methods. This thesis includes three main parts:In part one, the preparing process of ZnO/erythritol and Al2O3/erythritol composite PCMs and their properties were studied. The results of FTIR, XRD, TG and DSC testing showed that thermal conductivity of erythritol is obviously enhanced, and the enthalpy of the composite PCMs reached to300J/g, with only10%decrease compared with pure erythritol. It can be proved that there was neither chemical reaction within the composite-process, nor change in crystal structure, as could be proved by FTIR and XRD.In part two, soluble graphene was used to prepare graphene/PEG composite PCMs. Firstly, water-soluble graphene was synthesized from graphene oxide, and then ultrasonic in PEG aqueous solution, under heating and stirring to prepare graphene/PEG composites. TEM images indicated that graphene possess a transparent single-layer and slick surface. The thermal analysis showed that filled with4wt%water-soluble graphene, the thermal conductivity of PEG was increased by330%. SEM images indicated that graphene disperse uniformly in the PEG matrix. FTIR showed that no chemical reaction occurred in the compositing process of graphene.The synthesis process and properties of the hexadecanol nanocapsules were investigated in part three. The thermal conductivity was enhanced by improving heat transfer area. The nanocapsules were prepared by one step polymerization with hexadecanol used as core material, styrene as monomer. And the effect of the amount of chain transfer agent on structure of nanocapsules were studied. Through TEM, SEM, FTIR, XRD, DSC and so on, conclusions were made that the diameter of prepared nanocapsules were80~100nm, with a slick surface, and the latent heat of nanocapsules was reach to189.43J/g, with a core rate of70wt%. The prepared nanocapsules possessed a superior thermal stability to pure hexadecanol. The nanocapsulation process has slight effect on the chemical and crystal structure of hexadecanol.