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

Abstract

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