Preparation Of Reversible Photochromic Energy Storage Polyurea/polyurethane Microcapsules By In Situ Polymerization

Reversible photochromic energy storage polyurea/polyurethane microcapsules with latent heat storage and release,photochromic and other performances have attracted extensive attention,which can improve the leakage,overcooling and so on of phase change materials in actual use,and prevent the photochromic dye from being affected by external environments such as oxygen,p H and temperature.At the same time,it has important commercial value in the fields of outdoor wear,light decoration materials,anti-counterfeiting technology and so on.In this reaserch,polyurea microcapsules were prepared by one-step method(named as in-situ polymerization)with butyl stearate as the core material and the polyurea as the shell material which was synthesized by the isophorone diisocyanate(IPDI)and F2850,a new polyaspartic acid ester lipophilic amine.Firstly,the shell material was dissolved in the core material to form a homogeneous oil phase,and dissolving the oil phase in the water phase which was composed of the emulsifier aqueous solution,then they were subjected to shear and emulsification to form O/W emulsion,finally stirring and gradually heating up to obtain the microcapsules.And through the field emission scanning electron microscope(FE-SEM)analysis,the microcapsules were spherical with smooth and compact surface,uniform particle size distribution and the average particle size was 2.15 μm.What’s more,fourier transform infrared spectroscopy(FTIR)analysis showed that butyl stearate was successfully encapsulated by the polyurea shell.In addition,differential scanning calorimeter(DSC)results showed that the microcapsules could store and release a large amount of latent heat.They were excellent energy storage materials with the energy storage efficiency(E%)of 50.7%.According to the thermogravimetric analysis(TG),polyurea microcapsules exhibited good thermal stability.In order to optimize the synthesis process and improve the product quality,this reaserch also studied the main influencing factors in the encapsulation process,including different types of amines,the mass ratio of IPDI to F2850,emulsification speed and time.The results showed that when the amine was F2850,the microcapsules with smooth,dense surface and uniform particle size distribution could be obtained.And when the mass ratio of IPDI to F2850 was 1:2,the microcapsules presented the best shape and highest mechanical strength.In addition,the best emulsification speed was 10000 rpm and the emulsification time was 3 min.And the microcapsule samples exhibited excellent thermal stability and thermal cycling durability.What’s more,the photochromic microcapsules presented prominent light-to-thermal conversion properties,and the temperature of the reversible photochromic microcapsules was nearly 4.9°C higher than that of microcapsules at the same irradiation time.Due to the strong mechanical strength of polyurea and the strong rigidity of polyurea microcapsules,we introduced lipophilic polypropylene glycol(PPG)as the shell material to prepare polyurethane microcapsules.And the influence of the molar ratio of amine to alcohol,the ratio of core to shell and the alcohol of different molecular weight on the microcapsules was explored.The results showed that when the molar ratio of amine to alcohol was 3:1,the ratio of core to shell was 1:1 and the molecular weight of polypropylene glycol was 2000,the microcapsules presented good appearance,uniform particle size distribution and amazing latent heat storage and release performance,excellent thermal stability,prominent thermal cycling durability and excellent reversible photochromic performance.