Shape-Stabilized Phase Change Materials of Stearic Acid Confined in Fumed Silica

Abstract

Stearic acid (C18OOH) as a phase change material (PCM) possesses high potential for thermal energy storage applications. To prevent leakage of C18OOH in liquid state, a porous support is required to form shape-stabilized PCMs (SSPCMs) by impregnating C18OOH into the porous support. The SSPCMs were carefully investigated to demonstrate how the nanoconfinement in the porous support affects their thermal performance. In this work, a series of stearic acid/fumed silica (C18OOH/FS) SSPCMs with various C18OOH contents was fabricated, and their thermal characteristics were extensively examined. The FS provided an adequate inner void to confine up to 70 wt % C18OOH owing to its high porosity (88%). Meanwhile, C18OOH was well confined within the FS pore structure owing to hydrogen-bonding (H-bonding) interactions, surface tension, and capillary force. The SSPCM with an optimal content of 70 wt % C18OOH exhibited the melting and crystallization temperatures of 66.0 and 63.1 °C, respectively, which are slightly lower than those of pure C18OOH owing to the confinement effects. It also possessed good leakage resistance, a high crystallization fraction of 93.1%, and high thermal energy storage (TES) capacity of 146.3 J/g. Additionally, the composite exhibited excellent thermal cycling stability after 1000 melting/crystallization cycles. The thermal conductivity of the 70 wt % C18OOH/FS SSPCM (0.150 W/m·K) was lower than that of pure C18OOH (0.224 W/m·K), indicating that the SSPCM retards heat transfer during the heat charging and discharging processes. Generally, C18OOH/FS SSPCMs exhibit excellent TES capacity, high thermal cycling stability, and heat transfer retardation properties, with a facile preparation process at a low cost. Therefore, they are ready for industrial-scale applications in the fields of thermal insulation and thermal protection.