Study On Thermal Response And Photothermal Conversion Characteristics Of Thermochromic Phase Change Microcapsules

Thermochromic phase change microcapsules are a new type of intelligent material.The core material is mainly composed of a color developer（electron donor）,a color coupler（electron acceptor）and an organic solvent（phase change material）.At present,the research mainly focuses on monitoring the storage and release of internal energy through the expression of core material color,so as to play a certain indicative role,such as temperature sensor,anti-counterfeiting logo,textiles and intelligent pigments.In this study,from the perspective of thermal vibration of conjugated organic materials,the light capture ability of thermochromic phase change microcapsules was explored,and the thermal response performance of microcapsules was optimized,which further expanded the application field of thermochromic phase change microcapsules and provided a new choice for photothermal conversion materials.In this paper,blue and black thermochromic microcapsules were prepared by in-situ polymerization using ternary organic thermochromic materials as core materials and polymer organic polymers as wall materials.Nano-Al₂O₃ was used as hybrid agent to optimize the thermal response performance of microcapsules.The effects of core material ratio of ternary mixtures on the microstructure,particle size distribution,heat storage performance and visible light reflectivity of microcapsules were studied,and the optimum core material ratio was found.The chroma value of the best ratio before and after the phase change was tested,the corresponding color difference was quantitatively calculated,and the discoloration effect of the two types of microcapsules was analyzed and evaluated.The photothermal conversion performance of two types of thermochromic microcapsules was tested by simulated illumination experiment,and the corresponding photothermal conversion efficiency was calculated.The thermal response performance of thermochromic phase change microcapsules was optimized,and the effects of nano-Al₂O₃ content on the microstructure,heat storage performance and thermal response performance of microcapsules were characterized.The photothermal conversion efficiency before and after optimization was calculated and compared.By constructing the action principle diagram of the core material and wall material of thermochromic phase change microcapsules,the thermochromic mechanism,thermal response optimization mechanism and photothermal conversion mechanism were analyzed and revealed.The main work and research results are as follows:（1）Preparation of thermochromic phase change microcapsules.The microcapsules with morphology,phase change latent heat and encapsulation efficiency（>75%）,and core material ratio（1:3:60）have the best comprehensive performance.The color difference values of RTPCMs-C3 and RTPCMs-O3 before and after discoloration were 23.35 and 12.14,respectively.（2）Test and analyze the visible light absorption effect of microcapsules.RTPCMs-C3 has a strong absorption capacity for 550～630 nm yellow orange light in visible light.RTPCMs-O3 has a strong absorption capacity for 380～630 nm multi-color band in visible light.（3）Thermal response optimization of thermochromic phase change microcapsules.Through nano-Al₂O₃ hybrid thermochromic phase change microcapsules,the microcapsules have full particles and complete structure.When the content is 5%,the performance is the best,and the thermal conductivity is 0.2387 W/m·K.Compared with RTPCMs-0%,the thermal conductivity is increased by 61.3%.（4）The photothermal conversion performance of thermochromic microcapsules was investigated.The photothermal conversion efficiencies of RTPCMs-C3 and RTPCMs-O3 were 55.4%and 72.9%,respectively.The thermal response performance of microcapsules was optimized,and the photothermal conversion efficiency of RTPCMs-5%（C3）was increased by 11.5%.（5）As a high thermal conductivity material,nano-Al₂O₃ provides an efficient heat transfer channel for the propagation of phonons,enhances the diffusion strength of phonons,and heat transfer is more efficient.The structural formula in the ternary mixtures is changed,thereby improving the response of the microcapsules to temperature.（6）The conjugated organic core material selectively absorbs the electromagnetic radiation frequency matching its internal electron transition,causing the internal atomic lattice vibration to generate heat,resulting in the dissociation of the conjugated double bond between the color coupler and the color developer.The lactone ring in the color coupler is closed,and the color developer is also recombined with the proton,and the core color disappears.