Preparation And Properties Of Thermally Conductive PEG/PAM Composite Shaped Phase Change Materials

Phase change energy storage technology is currently an important way to improve energy efficiency and protect environment.Among the phase change materials,the most studied organic solid-liquid phase change materials have the advantages of large storage density,no supercooling and phase separation,low corrosivity and stable chemical properties.However,it is prone to leakage during use,and has a low thermal conductivity,which is greatly limited in practical applications.In this paper,organic solid-liquid phase change material polyethylene glycol(PEG)as phase change energy storage material,acrylamide(AM)monomer by free radical polymerization to form polyacrylamide(PAM)three-dimensional network as support material,introducing of Laponite clay(Clay)and reduced graphene oxide(rGO)as cross-linking agent and thermal conductivity enhancer to prepare shape-stabilized composite phase change material(ss-CPCM).Combined with the molecular dynamics simulation method,the thermal conductivity of the sample was simulated.Clay was introduced as physical crosslinks to prepare a series of PEG/PAM-Clay ss-CPCMs with different PEG content.Among them,the sample with 70 wt%PEG and 10 wt%Clay shows the best comprehensive properties,including high enthalpy of phase transition(110 J/g),good thermal stability and setting effect(leak rate of 8.72 wt%);thermal conductivity increased by 7.54%than PEG.Then introducing of partial reduction of rGO as a chemical crosslinkings to prepare enhanced thermal property of shape-stabilized PEG/PAM-rGO.Among them,rGO with different reduction degree were obtained by using sodium borohydride(NaBH4)reduction(SrGO)and low temperature reduction(LrGO)respectively.The results show that the enthalpy of the prepared all sample is higher than 145 J/g.The sample with 10%LrGO(PEG+LrGO10)has a excellent shape-stabilized properties with a leakage rate of only 0.26%.Moreover,PEG+LrGO10 exhibits good thermal performances:high thermal conductivity of 0.5234 W m-1·K-1(more than 63%increase over pure PEG),the heating time and cooling time were respectively 52.3%and 62.3%,shorter than that of PEG.At the same time,LrGO with higher reduction degree is better than SrGO in improving the thermal conductivity of ss-CPCMs.The thermal conductivity of PEG/PAM-rGO system with different rGO additions was calculated by the size effect method under the periodic boundary conditions with the method of molecular dynamics simulation.The results show that the thermal conductivity of the composite system increased greatly with the increase of rGO content.The simulated values of thermal conductivity,Maxwell-Eucken equation and experimental data fitted the same tendency.The rGO orientation in the composite system resulted in the thermal conductivity of the system anisotropy.Therefore,the method of molecular dynamics simulation can be used to guide the design of experimentally designed high thermal conductivity composite phase change materials,thereby reducing the number of sample preparation and saving manpower and material resources.