Study On Interface Structure Control And Thermal Properties Of Polyethylene Glycol/graphene Oxide Phase Change Materials

Thermal energy storage technology can be used to deal with the contradiction of the energy supply mismatch both in time and space,and store the excess or intermittent thermal energy and ruse during the specific period or a urgent demand,thus to enhance the utilization rate of energy as well as reduce the impact on the environment.Latent heat storage based on the phase change materials is one of the most effective ways for thermal storage,owing to its high energy storage density,isothermal characteristics and the tiny temperature difference between heat storage and release.So the technology has been widely considered as the perfect candidate materials in many different fields such as computer,motor,solar energy and the protection of electronic equipment.Polyethylene glycol(PEG)possesses many desirable advantages as phase change materials for the utilization in energy storage,such as high phase change enthalpy,good chemical stability,suitable phase transition temperature,non-corrosive,no pollution,and so on.However,the liquid phase leakage and poor thermal conductivity near the melting temperature are the major disadvantages of PEG phase change materials,which deadly limiting the application of PEG materials.In the present paper,graphene oxide(GO)is prepared via the modified Hummers method.The obtained GO has a very high specific surface area and high thermal conductivity,and its surface is rich in many oxygen-containing functional groups.Then PEG/GO composite phase change material is prepared by solution blending and characterized by a series of characterizations.FTIR and XRD results show that PEG and GO are linked based on hydrogen bonds and van der Waals forces,instead of chemical reaction.The SEM results showed that PEG and GO can be homogeneously mixed together,with good compatibility.When the GO content reaches 85%,the PEG/GO composite phase change material can effectively prevent leakage and achieve solid-solid phase transition.The crystallinity of PEG was inhibited and the phase change was reduced when addition of GO increase to a certain extent.However,the crystal morphology of PEG was relatively complete.Furthermore,when the content of GO is 15%,the thermal conductivity of the composite material increased nearly 6 times.Aiming at the decrease of phase change enthalpy of the as-prepared PEG/GO composite,PEG is grafted onto GO in the presence of toluene-2,4-diisocyanate(TDI)to prepared PEG-g-GO.Finally,similar experiment of PEG-g-GO and PEG is conducted to prepare PEG/PEG-g-GO composite phase change material.Take the sample with 85 wt% PEG,the characterization of TG and XRD show that PEG is successfully grafted onto GO during the grafting process and the grafted PEG show poor crystallization ability.XRD and DSC analysis showed that the modified PEG-g-GO had a weaker inhibitory effect on the crystallization and heat storage of the composite PEG,and the phase change enthalpy of the composite phase change material is relatively remained.As a conclusion,the addition of PEG-g-GO improved the thermal conductivity of composites.Then different proportions of GO/PEG-g-GO mixture are prepared and PEG/PEG-g-GO/GO composite phase change material is prepared using PEG-g-GO composite with 85 wt% of PEG.The synergistic effect of GO and PEG-g-GO on PEG materials is investigated.The results show that when the content of PEG-g-GO is 15%(ratio of PEG-g-GO/GO mixture),the phase change enthalpy of PEG/PEG-g-GO/GO composite is consistent with the theoretical phase change enthalpy.Furthermore,the good phase change energy storage capacity can be remained with no leakage problem.PEG/PEG-g-GO/GO with 85 wt% PEG and 15 wt% PEG-g-GO is used as stuffing materials to prepare a series of PVDF/PEGO dielectric composite films.The structural,dielectric and phase transition properties of the films is studied in detail.Results show that the dielectric constant of the film increases with the increase of the content of PEGO,this increase is more pronounced when the temperature is higher than the melting temperature of the PEGO.Near the percolation threshold(16 wt% PEGO)at 100 Hz,When the temperature raise from 20 °C to 70 °C,the dielectric constant of the film increased from 16.6 to 32.6,indicating that the PVDF/PEGO composite has better dielectric switching performance.In conclusion,the PVDF/PEGO composite is able to adjust the temperature owing to the fact that PEGO still remain phase change ability in the composite material.