Study On Polyethylene Glycol Composites As Phase Change Materials For Energy Storage

Since the 1970s,the energy and environmental problems have gradually aroused people's wide attention.Therefore,people began to investigate how to save energy and improve energy efficiency.At present,the use of phase change materials?PCMs?is an effective way for energy storage efficiency.Among them,polyethylene glycol?PEG?has the characteristics of greenness,non-toxicity,high phase change,and freedom of regulation.At present,the synthesis of PEG composites as PCMs for energy storage is complicated and the value of phase change enthalpy is generally not high.In this dissertation,sol-gel method was used to synthesize energy storage composites with high phase transition enthalpy and suitable phase transition temperature by using PEG as PCM.The leakage of PEG of the composites during the phase transition and the phase transition of the composite phase change energy storage material is limited by the pore structure of the mesopores.Following contents are included:?1?The preparation of PEG@TiO₂ as PCM for energy storagePEG was used as PCM to store and release thermal energy and TiO₂acted as the supporting matrix.PEG@TiO₂ composites with a series of differentmolecularweightofPEGwassynthesized.The micromophology,crystal structure and thermal properties were characterized by various techniques.The results indicate that core-shell structured PEG@TiO₂ composite was successfully synthesized.PEG was encapsulated in TiO₂ shell with physical interactions and crystallized without obvious restriction of TiO₂ on regular arrangement for crystallization.the highest phase change enthalpy of PEG6000@TiO₂ is137.4 J/g in the melting process and 133.3 J/g in the solidifying process with the mass fraction of 85wt%.And PEG6000@TiO₂ exhibited excellent thermal reliability based on the results of undergoing the heating-cooling cycle 50 times.Also,PEG@TiO₂ composite maintained good thermal stability within its working temperature range.?2?The preparation of PEG@SiO₂ as PCM for energy stotagePEG was used as PCM to PEG@SiO₂ store and release thermal energy and SiO₂ acted as the supporting matrix.PEG@SiO₂ composites with a series of different molecular weight of PEG was synthesized.The micromophology,crystal structure and thermal properties were characterized by various techniques.The results indicate that core-shell structured PEG@SiO₂ composite was successfully synthesized.PEG was encapsulated in SiO₂ shell with physical interactions and crystallized in SiO₂ shell without obvious restriction of SiO₂ on regular arrangement for crystallization.The highest phase change enthalpy of PEG6000@SiO₂ is150.9 J/g in the melting process and 145.7 J/g in the solidifying process with the mass fraction of 93wt%.It is a considerably exciting result as the value is so close to pristine PEG's?162.5J/g?.And PEG6000@SiO₂exhibited excellent thermal reliability based on the results of undergoing the heating-cooling cycle 100 times.PEG@SiO₂ maintained good thermal stability within its working temperature range.