Design of MtNS/SA microencapsulated phase change materials for enhancement of thermal energy storage performances: Effect of shell thickness

Abstract

Clay minerals are excellent supporting materials to synthesize shape-stabilized phase change materials (ssPCMs) because of outstanding pore structure, excellent thermal stability, perfect organic compatibility and eco-friendly features. However, previous clay-based ssPCMs show very low thermal energy storage capacity due to little loading of working PCMs (<65 wt%). In this work, stearic acid (SA) encapsulated by two-dimensional montmorillonite nanosheets (MtNS) has been designed in order to form core-shell structural MtNS/SA composite PCMs with ultra-high core mass fraction and dramatic latent heat capacity. This study mainly investigates the effect of MtNS shell thickness on thermal energy storage performances, including latent heat, thermal transfer ability, shape stability and cycling performances. Self-assembly mechanism of MtNS/SA was attributed to that the positively charged MtNS strongly attached on the surface of negatively charged SA latex particles and formed a core-shell structure mainly through electrostatic interaction. The MtNS/SA composite showed very large latent heat capacity (184.88 J/g) due to encapsulation of massive SA (>85 wt%). Besides, the composite PCMs also displayed improved thermal transfer ability due to the combination of MtNS, which leads to outstanding thermal charging/discharging rate and excellent photo-thermal conversion efficiency. It was also found that the thinner the MtNS, the better the thermal conductivity and latent heat storage capacity. In addition, the MtNS/SA composites show thermal and structural stability, no leakage occurred even under the encapsulation of the thinnest MtNS shell. Also, the cycling performances of this composite PCMs are very outstanding owing to the effective protection of MtNS shell. Hence, this non-leaking and green MtNS/SA composite PCMs with high-performance heat storage properties can be applied in sustainable energy field.