Preparation And Thermal Properties Of Flexible Phase Change Materials With Ionic Liquid

In order to solve the increasingly serious energy and environmental problems,it is urgent to develop renewable energy and improve energy efficiency.Using phase change materials to storage thermal energy can solve the imbalance of energy supply and demand in time and space and promote the development and popularization of renewable energy.As a new kind of phase change material,ionic liquid provides more choices and possibilities for the development of heat storage technology.To solve the disadvantage of ionic liquid,such as leakage,supercooling and low thermal conductivity,two different kinds of flexible composite phase change materials were prepared by post-filling of hollow fiber and electrospinning technique,respectively.The structure and properties of flexible phase change materials were tested.The effects of components on the structure and properties of flexible phase change materials were studied.The relationship between interfacial interaction and phase change behavior in composite systems was also analyzed.Flexible phase change filament with core-sheath structure was successfully prepared by post-filling of a polypropylene(PP)hollow fiber.The ionic liquid 1-butyl-4-methylpyridinium hexafluorophosphate was chosen as core component,while copper decorated muscovite(CuMVT)was synthesized via in situ reduction and used as the refining additive for the IL.Results from Differential Scanning Calorimetry demonstrated that the encapsulation ratio of the flexible phase change filament reached 93% with a fusion latent heat of 52.7 J/g at 48.3 °C.Supercooling of the ionic liquid was suppressed effectively as shown by the crystallization in the cooling step due to the addition of Cu-MVT.The flexible phase change material with core?sheath structure also showed good thermal stability,durability,and mechanical property under the protection of the sheath polymer material.Flexible phase change membrane based on ionic liquid/aluminum nitride/copolyamide composite were fabricated from electrospinning approach.The ionic liquid 1-hexadecyl-3-methylimidazolium bromide was chosen as phase change materials while nano-aluminum nitride(Al N)and copolyamide 6/12(Co PA)were chosen as additive and supporting matrix,respectively.The surface morphology and heat storage property had been systematically investigated by Scanning Electronic Microscopy(SEM)and Differential Scanning Calorimetry(DSC),respectively.Results showed that the diameter of the phase change fibers are 0.92～1.07 μm and was influenced by the IL and Al N content.With 57 wt.% of IL and 5 wt.% of Al N,the composite fiber achieved a fusion enthalpy of 86.4 J/g and the thermal conductivity was increased by 165.2% compared to that of IL/Co PA.Thermogravimetric Analysis(TGA)and thermal cycle test also indicated a good thermal stability and reusability of the composite fiber.Furthermore,Fourier Transform Infrared Spectroscopy(FTIR)and X-Ray Diffraction(XRD)analyses indicated that new hydrogen bonds between IL and Co PA were formed in the composite and showed a significant effect on the thermal performance of the composite fibers.The formation of hydrogen bond can prevent the leakage of IL,promote the crystallization process of IL and reduce its supercooling,increase its heat storage efficiency,but reduce the thermal storage capacity.