Enhancing freeze–thaw stability of phase change emulsions

Abstract

Phase change emulsions, which integrate the properties of heat transfer fluids with those of phase change materials (PCMs), offer promising applications in thermal energy storage systems. However, the widespread use of such emulsions, particularly those based on fatty acids, is hindered by their poor freeze–thaw cycle stability, which arises from interfacial destabilization and phase separation during repeated solidification–melting processes. This study addresses the challenge by developing a highly stable phase change emulsion using a stearic acid/stearic alcohol eutectic mixture as the PCM. By optimizing formulation parameters, including surfactant composition, co-surfactant ratios, and low-energy emulsification conditions, we achieved nanoemulsions with dispersed phase contents of 5%–20% and average particle sizes below 100 nm. Experimental analyses revealed that the emulsions exhibit exceptional physical and thermal stability, retaining consistent droplet size distribution and phase integrity after 600 h of static storage and 300 freeze–thaw cycles, a performance attributed to the suppression of Ostwald ripening and controlled crystallization. Moreover, the heat storage capacity of the emulsion reached 151.5% of that of water. These findings not only advance the practical applicability of phase change emulsions but also provide insights into the principles governing stability and phase behaviour in metastable emulsion systems.