Microscopic Mechanism Of Latent Heat Enhancement Of Modified Mineral-based Composite Phase Change Material

Porous mineral with high specific surface area and rich pore structure can effectively adsorb phase change materials into the pore structure through capillary action and surface tension,which is an excellent encapsulation medium for phase change materials.In this paper,to deal with the problems of latent heat limitation of mineral-based composite phase change materials,three kinds of composite phase change materials were prepared with expanded vermiculite(EVM),diatomite(DE)and palygorskite(PAL)as encapsulation media and polyethylene glycol(PEG)as thermal storage material by amination modification.Based on the systematic study of the phase change behavior and thermal storage performance of the composite phase change materials,and the microscopic mechanism of latent heat enhancement was revealed.A series of amination-modified EVM-based form-stable composite phase change materials(PEX fs-CPCM)were prepared by physical impregnation,and the optimal concentration of amination modification was explored,and the high encapsulation capacity(56.3～66.4 wt.%)and high latent heat(～144.0 J/g)were achieved.Moreover,new and weaker combination modes(O-H…N and N-H…O)were constructed for EVM and PEG to avoid the formation of strong hydrogen bonds(O-H…O),which reduced the surface limitation and tentatively explained the micro mechanism of latent heat enhancement.DE was chosen as another encapsulation medium,and the optimal concentration was followed to prepare the modified DE/PEG(MDP)composite phase change materials.It was found the amination modification also enhanced the thermal storage performance of MDP composite phase change materials,with an increase of ～25.42%in latent heat after modification.Especially,the latent heat of MDP fs-CPCM showed a significant increase from 0 to ～37.24 J/g,because amination modification weakened the interaction force between DE and PEG to reduce surface limitation,which was further demonstrated the universality of amination modification to enhance the thermal storage performance.The micro mechanism of latent heat enhancement of the amination-modified PAL/PEG(MPP)composite phase change material was quantitatively analyzed by combining experiments and simulations using PAL as the third encapsulation medium.The latent heat of MPP composite phase change material achieved significant enhancement from 0 to >37.63 J/g.The micro mechanism based on DFT calculations of latent heat enhancement could be described as: before and after modification,the surface interaction changed from weak Si-O chemical bonds to no combination approaches and the interaction energy sharply dropped from 195.25 e V to 0.40 e V,which provided direct evidence to explain why the surface interaction was greatly weakened and the latent heat was substantially enhanced.This article systematically conducted research on the amination modification of mineral-based composite phase change materials and the mechanism of latent heat enhancement.This provides a strategy for solving the problem of latent heat limitation in mineral-based composite phase change materials,and provides a reference for flexible regulation of the thermal storage performance of composite phase change materials.