Morphological control and thermal properties of nanoencapsulated n-octadecane phase change material with organosilica shell materials

Highlights: • Morphological control on NanoPCMs were realized by tuning various synthetic conditions. • Morphologies from thin-shelled nanocapsules to mesoporous particles were obtained. • NanoPCMs with thicker organosilica shells crystallize without supercooling. • Plausible mechanisms for the formation of various morphologies were proposed. - Abstract: Morphological control was attempted on organosilica nanoencapsulated n-octadecane phase change material by adjusting various synthetic conditions, and the relationship between morphology and phase change property was investigated. The chemical structure and thermal stability of the nanocapsules were characterized by FT-IR spectroscopy and thermogravimetric analysis, respectively. The morphology and microstructure of the nanocapsules were observed by SEM and TEM, and the phase change property was determined by DSC and temperature-dependent XRD methods. With decreasing water-to-ethanol ratio, increasing cetyltrimethylammonium bromide (CTAB) concentration, or increasing NH₃·H₂O concentration, the morphologies of the NanoPCMs can be regulated from thin-shelled nanocapsules with bowl like, hemispherical, or spherical geometries to thick-shelled spherical nanocapsules or mesoporous particles. Meanwhile, the average diameter of the nanocapsules also increases obviously. It was demonstrated that the phase change properties of these nanocapsules are intimately related to their morphologies: thicker organosilica shells induce heterogeneous nucleation better and result in less supercooling, compared with the thinner ones. The methods and mechanisms proposed herein might be helpful to prepare various micro/nano encapsulated phase change materials through interfacial hydrolysis–condensation method, and optimize their morphologies and thermal properties.