Increasing Phase Change Latent Heat of Stearic Acid via Nanocapsule Interface Confinement

Latent heat of phase change materials (PCMs) has long been regarded as constant. In this work, it is found that this parameter can be altered when they are in nanoscale. We designed and assembled a nanocapsule-confinement system with stearic acid (SA) sealed in silica nanoshells to investigate the thermodynamics and kinetics of their phase transition in nanoscale. It is interesting that heat storage capacity of the obtained SA@SiO₂ nanocapsules (NCs) could be increased up to 374.2 kJ/kg, about 36.9% more than that of the unconfined SA (273.3 kJ/kg). This is because the high superimposed stress from the curvature effect inside SiO₂ nanoshells would significantly shorten the intermolecular spacing of SA as compared to their unconfined state, which will especially strengthen hydrogen bonds of SA, forming multiple stable hydrogen bond networks. Therefore, breaking and reforming of these hydrogen bonds will no doubt contribute to latent heat of SA when they change from solid to liquid. Our results not only are helpful for understanding phase transition behaviors of phase change materials in nanocapsule interface confinement conditions but also provide a good example to develop new types of heat energy storage composite materials.