Preparation Of Polyethylene Glycol Form-Stable Phase Change Materials And Its Application In Light-Driven Thermoelectric System

Due to its high enthalpy and low supercooling,organic solid-liquid phase change materials(PCMs)have been widely concerned in the fields of solar energy utilization of medium and low temperature heat.Polyethylene glycol(PEG)is one of the most widely used organic PCMs.However the essential solid-liquid phase change flow and the lack of energy conversion function are the key problems to be solved in solar thermal utilization.It is an effective way to solve the leakage problem by introducing supporting materials into organic solid-liquid PCMs,however,the introduction of the supporting materials is often accompanied by a significant decrease in phase change enthalpy.The introduction of porous carbon support skeletons can realize the photo capture and photothermal conversion in the field of solar thermal utilization while giving the material shape-stability,but its high emissivity leads to low photothermal conversion and storage efficiency.In this thesis,aimed to solve above problems,PEG form-stable PCMs with high phase change enthalpy and efficient photothermal conversion were designed and prepared through giving the supporting materials phase change property and increasing selective absorption of carbon materials,and the photothermal conversion mechanisms were revealed.Moreover,the PCMs prepared in this thesis were applied to solar thermoelectric system,providing theoretical basis and new approaches for the practical application of PCMs in the field of solar thermal utilization and thermal management.Aimming at the phase change enthalpy reduced greatly after the introduction of supporting materials,according to the polycondensation reaction of diisocyanate and triisocyanates,linear phase change polyurethane(LPU)and 3D network phase change polyurethane(PC3D)were prepared,high phase change enthalpy PCMs based LPU(PEG/LPU)and high phase change enthalpy PCMs based PC3D(PEG/PC3D)were obtained by further loading PEG.Due to the supporting and phase change characteristics of the supporting materials itself,PEG/LPU and PEG/PC3D both have good shape-stability and high phase change enthalpy(119.8～147.5 J/g and 169.7～194.5 J/g).To solve the problem of low photothermal conversion efficiency of carbon-based PCMs,three kinds of photothermal conversion form-stable PCMs were designed based on solar energy spectral energy distribution:Dye-PCM,Fe2O3-RGO/PCM and Ag-RGO/PEG.The enthalpies of the three PCMs are 112.9 J/g,167.6 J/g and 166.1 J/g,respectively.All the three materials exhibit selective absorption in the region with the strongest visible light energy,realizing efficient photothermal conversion and thermal storage,with the efficiencies of photothermal conversion and thermal storage reaching 72.0%,96.4%and 92.0%,respectively.The photothermal conversion mechanisms of the three materials were also explored.It provides theoretical basis for the preparation of high efficiency photothermal conversion PCMs.Two kinds of form-stable phase change cold storage materials were designed and synthesized,and based on the cooling insulation characteristics of phase change cold storage materials,temperature control and photothermal conversion of photothermal PCMs,the phase change cold storage materials and the photothermal PCMs designed and synthesized in this thesis were used as the hot-and cold-side materials of thermoelectric modules,respectively,to construct the solar thermoelectric system.The hot-side materials can realize the efficient absorption and photothermal conversion of sunlight,and cooperate with the cold-side to realize the temperature control,so as to obtain a stable temperature difference and current output within a certain period of time.Further optimization of the constructed solar thermoelectric system,based on the phase change optical control characteristics of vanadium dioxide(VO2)film,to achieve further regulation of sunlight,and build an intelligent solar thermoelectric system.