| Currently,energy consumption and renewable energy utilization become the major issues,and thermal energy storage is considered as the promising technology to meet the future energy needs.Due to advantages of low cost,large storage capacity under isothermal conditions,phase change materials(PCMs)are used as thermal energy storage materials to solve the energy crisis.Organic thermochromic materials are composed of three substances including colorant(thermochromic dye),developer and co-solvent,which can not only realize latent heat storage-release,but also provide real-time evidence of energy saturation and consumption,attracting widespread attention of researchers.The microencapsulation technology can realize the storage and transportation of organic thermochromic materials,prevent contamination and corrosion,and realize the energy exchange with external environment in terms of time and space.In view of the current preparation methods of thermochromic microencapsulated phase change materials,the relevant research including the synthesis process of in-situ polymerization method,the color development mechanism,temperature-induced crystallization and color change,performance optimization and applied research of temperature adjustment is carried out:(1)The reversible thermochromic microencapsulated phase change materials are synthesized via in-situ polymerization.The relation between encapsulation conditions such as molecular weight,the type of molten salt and additive amount of styrene maleic anhydride copolymer,the p H value of the system,the stirring rate,the core/shell ratio and performance of products is discussed in detail.RT-MPCMs present smooth spherical surface and clear core-shell structure(average shell thickness:50?60 nm),the average particle size around 440 nm,excellent latent heat storage capacity(?H_m=165.9 J/g,?H_c=165.3 J/g)and outstanding thermal stability.RT-MPCMs show good cycle durability and thermal reliability via 100 thermal cycle tests.The thermal protective clothing containing reversible thermochromic microencapsulated phase change materials is designed and prepared to realize providing adequate thermal protection in the fire environment.(2)Methylated melamine formaldehyde resin prepolymer(MMF)and melamine formaldehyde prepolymer(MF)are selected as shell materials,the influence of shell materials on the thermochromic properties of microcapsules is discussed in detail.Ag NPs is obtained via oxidation-reduction method to be employed as modifier of microcapsule,the Abs values of staphylococcus aureus bacteria liquid and escherichia coli bacteria liquid with RT-MPCMs(B)modified by Ag NPs(Ag-RT-MPCMs,Ag NPs:0.25 wt%)were 1.049 and 0.740 via ultraviolet-visible spectrophotometry.Ag NPs can be used as heterogeneous nucleating agents and have effect on heat transfer mode of RT-MPCMs and the sensitivity of thermochromic phenomena.The results show that the melting enthalpy and crystallization enthalpy of Ag-RT-MPCMs increase to 170.2 J/g and 168.9 J/g,the discoloration temperature reduced from 38?to 33?.(3)The microstructure and shell composition of the reversible thermochromic microencapsulated phase change materials are critical to its performance.The high reactivity between the isocyanate of toluene diisocyanate and the active hydrogen of the methylolamino resin is used to obtain the hydrophobic amino resin shell.Using thermochromic microcapsules as template,new type thermochromic microcapsules with of hydrophobic amino resin shell is prepared via surface modification of isocyanate groups,the water contact angle of product increases from 0°to 148.5°.(4)The shell layer is modified to improve the mechanical properties and anti-permeability properties of the thermochromic microcapsules,so that they can maintain the complete structure during the application process.The water-soluble polymer polyvinyl alcohol(PVA)was selected as the modifier,and the influence of PVA/MF feed ratio,PVA modification method and PVA type on the performance of thermochromic microcapsules was investigated in detail.PVA can react with the methylol in the system to improve the crosslinking degree of resin.When the feed ratio of PVA-2699/MF is in the range of 0.04?0.25,the mechanical properties and permeability resistance of RT-MPCMs are effectively improved.(5)ODB-2 as the thermochromic dye,bisphenol A as the developer and methyl stearate(Me S)as co-solvent are selected to prepare reversible thermochromic materials,which is employed as core materials.Reversible thermochromic microencapsulated phase change materials obtained via in-situ polymerization present stable light-to-heat conversion capability(?=86.9%),excellent latent heat storage-release performance(?H_m=171.9 J/g,?H_c=171.4 J/g)and heat storage capability(C%=99.6%),can monitor status of latent heat storage-release through color change.The temperature inducibility of thermochromic microcapsules is investigated through microscope,small-angle/wide-angle diffractometer and in-situ X-ray diffractometer in detail.The narrow-dispersion composite macrocapsules are prepared via piercing-solidifying incuber method and wearable smart sleeves are obtained by employing non-woven fabrics as base to explore its practical application value in the fields of intelligent temperature regulation and thermal management. |
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