Synthesis Of Shape-stabilized Phase Change Materials With Carbonaceous Materials And Their Thermal Properties

PEG with different molecular weight from 100 to 20000 was treated as excellent polymeric PCMs due to its relatively high latent heat storage capacity,suitable phase change temperature from 3.2 to 68.7 ℃,non-corrosiveness,non-toxicity and chemical stability.However,PEG is the same as other organic PCMs,and has very low thermal conductivity,leakage during phase transition,and dramatic decrease of the heat transfer rates in large-scale energy saving applications.In the view of those defects of the PEQ shape-stabilized phase change materials were designed to improve or solve these problems.In our work,graphene oxide and graphene aerogel were utilized as supporting or packaging material to improve the thermal properties of the PCMs and keep them shape stabilized during the phase change process.The main works are as follows:(1)Polyethylene glycol(PEG)based shape-stabilized phase change materials(PCMs)were successfully synthesized by a facile and effective physical blending method with the assistance of microwave.Graphene oxide(GO),as a supporting material,was added in PEG matrix to improve the thermal properties of PCMs and keep their stabilized shape during the phase change process.With the assistance of microwave,the interlayer spacing of GO sheets was expanded and the entire blending process was time saving.A small content(about 4 wt%)of GO could make the composite absorb energy efficiently without leakage during their phase change because of the hydrogen bonding and capillary force between the GO layers and PEG molecular chain.The DSC results showed that the composites had a heat storage capacity of 174.5 J/g,which was 95.6%of the phase change enthalpy of pure PEG.The photo-thermal energy conversion of the composites was explored.(2)A facile one step hydrothermal was used to prepare the three-dimensional graphene aerogel confined PEG based phase change materials.During the hydrothermal process,the oxygen-containing functional groups of the GO sheets would be decomposed and the nanoplates were assembled around the PEG molecular chains to form a 3D network.In the traditional two step synthesis,synthesis of three-dimensional graphene aerogels was prepared before;then,the PCMs were blend with the graphene aerogel by physical adsorption.Compare with the traditional process,the composite phase change material prepared by our one step method mixed more evenly.It can be proved by FT-IR that no chemical reactions took place but inter-molecule hydrogen bond existed between graphene sheets and PEG molecule chain.The composites PCMs could stay form-stabilized during the whole leakage test without obviously leakage when the GA content increased to a certain degree.The homogeneous interconnected 3D and hollow porous networks of the self-assembly graphene aerogel would confine the movement of molten PEG molecule chains.The homogeneous interconnected 3D and hollow porous networks of the self-assembly graphene aerogel would promote the thermal conductivity greatly yet decrease its crystallization slightly.The leakage test results show that only PEG 1 and PEG2 would slightly leak out during the progress.The composites could stay shape-stabilized when the graphene aerogel content more than 9.8 wt%.The composites had a heat storage capacity of 164.9 J/g in melting process and 158.1 J/g in crystallization kinetics,respectively.These composites are still hold good thermal energy storage performance.