Preparation And Properties Of Nanoencapsulated N-octadecane Phase Change Material With Organosilica Shell

Phase change materials (PCMs) have attracted much attention in the last decades because they can provide high energy storage density and near isothermal heat storage. Therefore, PCMs can be applied in fields of thermal energy storage, building energy conservation, industrial refrigeration system and so on. Micro/nano encapsulation of PCMs with protective shell materials is a good way to prevent the PCMs from leaking during the process of solid-liquid phase change, including increasing the heat transfer area, controlling the volume changes during the period of phase change and reducing the PCM reactivity towards the outside environment.In this paper, a series of organosilica nanoencapsulated n-octadecane phase change materials were prepared through interfacial co-hydrolysis and co-polycondensation of functional silane precursors in miniemulsion, including tetraethyl orthosilicate (TEOS), γ-methacryloxypropyltrimethyl silicate (MPS), and methyltrimethoxy silane (MTMS).The morphology, phase change property and hydrophilic/hydrophobic property were studied by changing the volume ratios of MPS/TEOS or MTMS/TEOS. The results show that the prepared organosilica nanocapsules (200-693 nm) with well-defined core-shell structure and high phase change enthalpies (100J/g). With increasing the volume ratios of MPS/TEOS or MTMS/TEOS, the contents of organic groups in the shells become increasing, the morphologies of the nanocapsulated phase change materials transition from spherical to bowl like shape and also the hydrophobicity of shell can be improved. When the organosilica shell material is prepared by using MTMS as silane precursor solely, its surface becomes super-hydrophobic and the water contact angle up to 155°.The morphologies and thermal property of organosilica nanoencapsulated n-octadecane were studied by adjusting various synthetic conditions, including water-to-ethanol ratio, emulsifier, and NH3·H2O concentration, the mechanism was analyzed. SEM and TEM results indicated that decreasing water-to-ethanol ratio, increasing cetyltrimethylammonium bromide (CTAB) or NH3·H2O concentration, the shells of NanoPCMs get thicker, and the core-shell structures turn to solid nanoparticles. Due to the structural flexibility of organosilica shell materials, the thin-shelled nanocapsules are capable of deformaion, which produces bowl like, hemispherical, or non-spherical geometries of morphology. Founding that 2-3 phase transitions may exist during the solidifying process of these NanoPCMs with different morphologies and farily high phase change enthalpies(-100 J/g), which induced by the nanocapsule shell materials.On the basis of methacryloxypopyl modified silica shelled NePCMs prepared in chapter 2 and 3, preparation of polymethacrylate/silica hybrid shelled NePCMs were attempted by conducting further free radical polymerization. The influences of different reaction approaches and reaction times on the morphologies and properties of the hybrid shelled NePCMs were investigated. The results indicated that it is viable to achieve organic-inorganic hybrid shelled NePCMs by combining interfacial hydrolysis-condensation reaction and free radical polymerization in mimiemulsion.