Preparation And Properties Of Porous Framework/phase Change Materials Based On Colloidal Agglomeration

With the rapid development of global economy,the rate of energy consumption has exceeded expectations.In addition to developing new energy alternatives,strategies developed to increase the utilization efficiency of existing energy sources also aroused considerable attention,such as recovering industrial waste heat and storing idle electrical energy.Heat energy is closely related to human life and social production,as most of the energy was consumed by people in the form of heat energy.As the most promising thermal energy storage(TES)medium,phase change materials(PCM)are widely used in TES systems to achieve the purpose of improved utilization efficiency.At present,organic phase change materials(OPCM)have many advantages in the field of thermal energy storage due to their excellent performance,such as no undercooling or low undercooling,stable freeze-thaw cycles,and no phase separation.However,low thermal conductivity,leakage and flammability issues restrict their application as TES materials.Therefore,how to enhance thermal conductivity,control leakage and reduce flammability is very important for OPCM.To prevent the OPCM from leaking during the phase change process,shape stable technology has been widely adopted currently for its effectiveness.The supporting material limits the OPCM in the porous skeleton to prevent the leakage during the melting process from interacting with the surrounding environment.The capillary force and surface tension further ensure the structural stability of the composite material,thereby improving the efficiency and safety of the material.More importantly,the porous skeleton serves as a shape-stable substrate and provides heat transfer path,while solving the problem of low thermal conductivity and leakage.There are two main ways to improve the flame retardancy of PCM.The first method is physically mixing flame retardants,but it brings the issue of imcompatibility and large consumption of flame retardants.The second method is chemical modification,that is,the flame-retardant element is attached onto the supporting framework or OPCM chain via chemical grafting.Compared with the modified skeleton,the chemical structure of OPCM was more stable after modification,as well as no self-heating vaporization.Therefore,chemical modification of OPCM is considered as a better solution.Based on the above viewpoints,the specific work in our research is as follows:(1)The reduced-graphene oxide aerogel(rGO aerogel)was prepared by the colloidal aggregation method,and then the rGO aerogel/eicosane composite phase change material was obtained by self-diffusion.The energy storage potential and photothermal conversion efficiency of composites have been explored.Differential scanning calorimeter(DSC)test results showed that the phase change enthalpy of the composites is proportional to the mass fraction of eicosane.it's the enthalpy value of PCM4 with 97%eicosane is 214.8 J/g.After 50 phase change cycles,the DSC curves basically overlap,which proves that the composites have excellent cycle performance.The highest thermal conductivity of the composite material is 0.4221 W/m·K.The composite material was irradiated with a solar simulator,and its photothermal conversion efficiency was tested and calculated to be about 55%.(2)Stearyl alcohol(SAL)was chemically grafted with POCl₃to obtain modified SAL,and the porous SWCNT skeleton was prepared by colloidal agglomeration method.Finally,a series of composite materials were prepared by the self-diffusion method.The appearance of the P-O-C bond from chemical structure characterization proved that SAL was successfully modified with P element.Compared with SAL,the thermal stability of modified SAL was increased by 7.14 wt%,and the phase change enthalpy was 156.5 J/g.The thermal stability and energy storage potential of the composite material are proportional to the content of modified SAL.The flame retandance testing showed that the peak release rate(PHRR)value decreased from1157.0 to 772.6 W/g,and the total heat release(THR)also decreased from 30.1 to12.3k J/g.Through flame-retardant mechanism analysis,the synergistic effect of SWCNT skeleton and modified SAL in the flame-retardant process was confirmed.