Regulation of thermal conductivity of microencapsulated phase change materials via atomic layer deposition

Abstract

Microencapsulated phase change materials (MEPCMs) have different thermal conductivity requirements under various application conditions. Organic-shell MEPCMs currently dominate the microcapsule due to their easy availability. The aim of this paper is to regulate the thermal properties, especially the thermal conductivity, of organic-shell microcapsules. Herein, with the precision and uniformity of atomic layer deposition (ALD) coating, the thickness of ZnO coating is controlled on the surface of paraffin @ polymethyl methacrylate (PMMA) to realize the regulation of thermal properties of MEPCMs. The experimental results illustrate that the introduction of ALD ZnO shell abates the phase transition enthalpy of MEPCM, but it realizes the optimization of thermal stability and phase transition reversibility for MEPCMs, which is confirmed by the mechanical test results of microcapsules. Furthermore, it is particularly worth mentioning that the thermal conductivity of MEPCM can be adjusted from 0.16 to 1.99 W m−1 K−1 within the ALD cycle range given in this research. The equivalent thermal conductivity of MEPCM was verified by calculation, and the relationship between ALD treatment and thermal conductivity was obtained. This research provides a strategy for accurately regulating the thermal conductivity of phase change microcapsules, breaking through the bottleneck in the application of microcapsules.