Preparation And Properties Of Aerogel Based Shape-stabilized Phase Change Energy Storage Materials

Organic phase change materials(PCMs)play an important role in thermal energy storage because of their excellent properties such as large latent heat,low undercooling and adjustable phase transition temperature.However,they are constrained by the problems of flow and leakage in the process of solid-liquid phase transition.Therefore,it is imperative to prepare a kind of shape stabilized phase change materials(ss PCM).It is one of the most promising methods to prepare ss PCM by injecting PCMs into porous frameworks.In this paper,we have prepared a series of aerogels with different pore structure and surface properties.The PCMs are injected into the porous framework of aerogels through vacuum impregnation.Then,the aerogel based phase change energy storage composites were obtained.We explored the effects of the amount of precursors,the amount of surfactant cetyltrimethyl ammonium bromide(CTAB),the ratio of ethanol to water,and the concentration of different alkaline catalysts on the microstructure of aerogels.It is found that surfactant has the most significant effect on the microstructure of aerogels.With the increase of surfactant,the agglomeration of aerogel particles decreases,the specific surface area increases,and the average pore size is concentrated in the mesoporous range.When the amount of CTAB is 3 g,the specific surface area of aerogel can reach 608 m~2/g,and the pore volume can reach 1.08 cm~3/g.The loading rate of aerogel for PCM is as high as 876%.The enthalpy of ss PCM is 122.9 J/g.At the same time,the ss PCM has good thermal cycle stability.After 50 melting-crystallization cycles,the ss PCM still keeps 97%of its mass,and the phase change enthalpy is 97%of the initial thermal cycle.In order to simplify the experimental process,we explored the preparation of MTMS aerogel by one-pot method.The one-pot preparation method effectively overcomes the problem of phase separation of precursors,and can easily prepare aerogels with ultra-low density,high porosity and transparency.When the volume of acetic acid is 100 m L,the BET area of aerogel is as high as 643 m~2/g,the pore volume is 1.07 cm~3/g,the average pore size is 12.1 nm,and the density is only 0.048 g/cm~3.The aerogel prepared in this chapter has a high loading rate of 1561%for PCM.In order to enhance the interaction between porous scaffold and PCM,we have copolymerized 3-aminopropyltriethoxysilane(APTES)with MTMS and successfully grafted aminopropyl group to the surface of aerogels.The amino modified aerogels can be prepared by this copolymerization method.The aerogels have a large specific surface area of up to 579 m~2/g,the maximum pore volume can reach 1.58 cm~3/g,and the pore size of aerogels is mainly concentrated below 40 nm.The loading rate of ss PCM is as high as 920%.After 50 melting-crystallization cycles,the load rate is still as high as 837%.In terms of the enthalpy of transformation,the enthalpy of ss PCM transition is 109%of pure PCM and 86.5%after 50 melting-crystallization cycles due to the confinement of aerogel pores.In order to enhance the mechanical properties of aerogels,we have copolymerized vinyltrimethoxysilane(VTMS)with MTMS.When the precursor ratio is 1:5,the BET area is 352 m~2/g,the pore volume is 0.47 cm~3/g,and the average pore diameter is 7.2 nm.At the same time,aerogels have good compressibility.After 50 melting-crystallization cycles,the loading rate of ss PCM decreased from 759%to 689%.For example,the melting enthalpy of paraffin is 88.9%of that of pure PCM.It is decreased to 77.8%after50 melting-crystallization cycles.This article explores the application of MTMS aerogel in the field of ss PCM.The research shows that the shape?stabilized phase change composite material prepared by MTMS aerogel as the framework has extremely high loading rate,high phase change enthalpy and good stability.This new type of composite material has potential application value in fields such as thermal energy storage and thermal management.