Preparation And Properties Of Phase Change Material Nanoparticles Based On Phase Inversion Emulsification

Phase change materials are widely used because of their good thermal control and heat storage performance, but phase transition will limit their application during the process of utilization. Encapsulated phase change materials (EPCMs) can prevent PCM from leaking in the process of liquid-solid transition, which has been more widely applied in architectural materials, thermo-regulated textiles, aerospace field and others. The preparation of emulsion is very important during the preparation of EPCMs. The emulsion inversion point (EIP) method is a kind of low-energy emulsification method. EIP was used as a preparation method to synthesize EPCMs. It overcomes the shortcomings of the traditional high energy emulsification method, which has the advantages of low energy utilization, high cost and poor environmental protection.Nanoencapsulated phase change materials (Nano-PCMs) containing n-octadecane were synthesized with polymethyl methacrylate as shell, Sorbitan oleate (Span 80) and polyoxyethylene sorbitan monolaurate (Tween80) as emulsifiers, azodiisobutyronitrile (AIBN) as initiator, using a phase inversion emulsification method and free radical polymerization. The effect of the ratio of wall material monomer and its prepolymer on the properties of the nanocapsule was studied by using dodecyl mercaptan (DDM) as a chain transfer agent. Furthermore, the surface morphologies, crystallization properties, and thermal stabilities of NanoPCMs were investigated using scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TG) and fourier transform infrared spectrometer (FTIR), respectively. Based on the theory of Toraz and Mason, we discussed the spreading coefficient of oil, water and polymer in different emulsifier content. From the viewpoint of thermodynamics, a comparative study of the predicted morphology and the actual morphology of the capsule was carried out. In the process, the surface tension and interfacial tension were calculated by young’s equation, Fowke equation and harmonic equation.The results showed that optimal content of initiator, emulsifier and the polymerization temperature are 0.4 g,7 g and 73 ℃, respectively. The particle size of Nano-PCMs is 200-500 nm. The surface of Nano-PCMs is relatively smooth and compact without holes and sinks; part of prepolymer in monomer were favorable for the formation of the nanocapsules. The reaction time of the prepolymer and core/cellratio to prepare nanocapsules have little impact on the particle size and morphologiesof the nanocapsules. But it had a significant effect on the heat enthalpy. When the reaction time of preparing prepolymer is 20 min and the core/cell ratio is 9:10, the encapsulation rate is the highest. And the particle size distribution of prepared nanocapsules is uniform and have about 150 ～ 300 nm in the average diameter. Also, nanocapsules have smooth surface and good heat stability. With Span80 and Tween80 (HLB=9.8) as emulsifier, the system has good stability. The predicted morphology of the capsule was not entirely consistent with the actual shape of the capsule, which showed that the morphology of the capsule was not only affected by the thermodynamic factors but also by the kinetic factors.