Preparation and application of a high thermal conductivity phase change microcapsules with fluorescence characteristics based on ZnWO4 shell

The phase change microcapsules (NePCMs) with high latent heat values, thermal conductivity and stability were synthesized by coating stearic acid (SA) phase change material (PCMs) with Zinc tungstate (ZnWO4) as the shell material. The prepared ZnWO4 and microcapsule samples are characterized through various techniques, and their thermophysical properties under different core-shell ratios and emulsifiers are compared. The highest phase transition enthalpy reaches 83.63 J g-1 when the core-shell ratio is 1:1 and the sodium dodecylbenzenesulfonate (SDBS) is adopted as the emulsifier. Based on SEM and TEM results, the regular spherical shape and complete core-shell structure of the microcapsule can be found, and the particle size ranges between 100-300 nm. The thermal conductivity of the SA has increased by 141.18%~238.43% after by using the ZnWO4 as the shell material. Moreover, thermogravimetric and leak-proof performance tests demonstrated that microcapsule samples possess a high thermal stability. There was no leakage from the six microcapsule samples after heating, proving their potential application for thermal energy storage (TES) under long-term high-temperature conditions. In addition, the cost of ZnWO4 prepared by this method can be reduced about 40%. According to UV absorption and fluorescence spectrum evaluation, ZnWO4 and microcapsule samples have good photoluminescence and UV absorption properties, making the sample can be widely employed in fluorescent construction, coatings and textile industries with a lower cost.