Diverting phase transition of high-melting-point stearic acid to room temperature by microencapsulation in boehmite

Organic phase change materials (OPCMs) have long been recognized as potentially reversible thermal energy storage candidates due to their ability to reversibly store or release large amounts of latent heat when changing from one physical state to another. For application of which in solar heat storage, reducing their relatively high phase transition temperature (T_C) to room temperature is still challenging. Herein, a microemulsion with metastable interface is adopted for in situ synthesis of sphere-like structure stearic acid (SA)@boehmite (γ-AlOOH) microcapsules. Interestingly, when the high-melting-point SA crystals (T_C = 70.8 °C) were capsulated into boehmite nanoshells, their phase transition could be diverted to room temperature (∼21 °C), which means about 50 °C decrease of their phase change temperature has been achieved. This dramatic change could be due to a confinement effect on the interface between SA cores and the boehmite nanoshells, which leads to a change of geometric factors and enhancement of shell-SA interactions. Furthermore, the heat energy storage density (∼140 kJ kg^-1) of the obtained SAγ-AlOOH microcapsules is higher than that of most common room temperature PCMs, suggesting an efficient heat storage ability. This kind of shape-stabilized microcapsule can be considered as candidate room temperature PCMs for thermal energy storage.