Structural Design And Properties Of Novel High Performance Phase Change Material

Most of the widely studied organic phase change materials belong to the solid-liquid phase change materials,which exist the shortcoming of leakage during the endothermic melting process,which makes it difficult for practical application.In addition,the organic solid-liquid phase change materials also perform in poor thermal conductivity,which leads to the slow thermal response rate and makes it greatly reduce their heat storage efficiency.Therefore,this thesis focuses on preparing three kinds of composite phase change materials via micro-nano encapsulation,3D porous matrix encapsulation and graft polymerization respectively.The details are described as following:(1)The novel microencapsulated phase change materials,which based on n-octadecane core and nano-Zn O/melamine-formaldehyde resin shell,were prepared by in-situ polymerization.The particle size of this microencapsulated phase change materials is about 10?m and their latent enthalpy reaches 123.90 J/g.While the content of nano Zn O in the shell reaches 7 wt%and the coating rate reaches a good value of51.40%due to their excellent micro-spherical micro-encapsulation structure.The above encapsulation properties make it retain the original heat storage performance in 100thermal cycles test.Besides,the microencapsulated phase change materials show excellent light-heat conversion characteristics under light illuminating,their highest photothermal conversion efficiency reaches 75.2%.(2)The 3D manganese oxide foam was prepared by Ka Mn O₄,Na OH and Mn Cl₂·4H₂O and via hydrothermal reaction,self-assembly and freeze-drying.On this basis,manganese oxide nanorod-based foam was used as the supporting material,polyethylene glycol(PEG-6000)with a weight average molecular weight of 6000 was used as the phase change material and the composite phase change material was prepared by vacuum impregnation.The composite phase change materials obtain a heat storage enthalpy of 125.35?164.86 J/g and its optical absorption performance over 90%.Furthermore,the composite phase change materials heated up over 70? after light illuminating due to the electron transition and energy release phenomenon of manganese oxide nanorod,indicating that composite phase change materials possess excellent photothermal conversion properties.(3)The high thermal conductive composite solid-solid phase change materials were prepared by graft polymerization,which consists of PEG-8000 phase change materials and GO/h-BN@MDI matrix.The composite phase change material mainly forms a stable cross-linking structure by the bridge bond,which synthesized by the reaction of the active functional group with the isocyanate root.And the cross-linking structure consists of“soft segment”and“hard segment”,which are the phase change materials and the matrix,respectively.The heat storage enthalpy of composite phase change materials exhibits in a range of 123.42?155.71 J/g,and the maximum heat storage efficiency reaches 98%.Moreover,its thermal conductivity has been greatly improved,and the maximum thermal conductivity reaches 0.574 W/m K.