Studies On The Preparation Of Silica Microspheres And Their Application In Micro-Encapsulated Phase Change Materials

Since the surface of silica microsphere owns a large number of hydroxyl groups, as well as its small particle size, larger surface area and good dispersion, it can exhibit excellent chemical stability, reinforcing, thickening and thixotropy and has been widely used in industries including catalysts, ceramics, pigments, pharmacy, etc. However, the particle size of silica microsphere is a critical factor for its performance and application, therefore, it is necessary to control its particle size.Micro-encapsulated phase change materials use phase change materials to regulate the surrounding temperature, they are promising materials applied into the field of aerospace, building energy conservation, clothing textiles, medicine field and so on. Becouse the wall material usually adopts polymers that limits the performance, in order to improve their property, other particle ought to be filled in to come up to the application requirement.In this paper, silica microsphere was prepared by a sol-gel method, and the control on the particle size of the prepared silica was emphatically studied through adjusting the reaction temperature and the concentration of the raw materials (ethanol, ammonia and TEOS). The result of XRD measurement showed that the product was amorphous. Based on silica microspheres morphology studies, the average size of the product increased from0.66μm to0.90μm when ethanol concentration increased from7.14M to9.55M and the reason might be the increasing concentration of ethanol promoted the hydrolysis of TEOS system. With the concentration of ammonia increased from1.88M to2.36M, the size of silica microspheres increased from0.50μm to0.90μm. The reason is that taking ammonia as the catalyst can enhance the polymerization formed by reaction short chain between the crosslinking, resulting in the formation a larger size of silica microspheres. When the concentration of TEOS increased from0.08M to0.11M, silica particle size increased from0.47μm to0.90μm. The reason is increasing concentration of TEOS accelerated the reaction, it may lead to the increasing of silica particle diameter. Further research shows that silica microsphere particle diameter increased from0.71μm to0.83μm when the reaction temperature increased from26℃to28℃and then as the reaction temperature continued to increase to32℃, particle diameter of product reduced to0.66um. Through the above integrated regulation of reaction temperature and concentration of the material, it’s achievable to get the particle size of silica microsphere controlled between the0.47～0.90μm.On the surface of core material butyl stearate polymerizated urea-fomaldehyde resin to prepare micro-encapsulated phase change materials and filled microsphere into wall material, through designing orthogonal design table, the influence of micro-encapsule’s phase change thermal storage and sealing performance can be analyzed by studying he size filling volume and the molar ratio of formaldehyde and urea. DSC results showed that the phase transition enthalpy of microcapsules is significantly influenced by the molar ratio of formaldehyde to urea, and adding appropriate amount of silica microspheres can increase the enthalpy of microcapsules. Analysis of breakage rate of microcapsules suggested that filling volume of silica microspheres is a significant factor to affect the rate and filling in proper amount of silica microspheres can decrease the breakage rate of microcapsules. The reason is that when the microcapsules suffered the shear stress, the craze and crack appeared, the stress concentration effect happened because of the interaction between microcapsules which own small size and Urea-formaldehyde resin to make the atrix yield and appear plastic deformation, what’s more, they absorbed impact energy to transform the crack to craze, preventing the leak of liquid core material butyl stearate and making the wall possesses the shear performance. Analysis of factors influencing denseness showed that it is significant when filling volume of silica microcapsules is in the significance level of0.05and particle size of silica microcapsules is in the significance level of0.10and filled proper amount of silica microcapsules can hence the compactness of microcapsules. Because part of silica sphere would embedded into the micro porous of wall material when filled silica sphere into wall material of microcapsule that made the size of the micro porous of wall material of the microcapsule small or the quantity little and slowed down the release rate of the microcapsule and improved the denseness. We identified the best formula of silica microspheres filled micro-encapsulated phase change materials by comprehensively analyzing results of range and variance of the three main performance of enthalpy, breakage rate and denseness:when particle size of silica microspheres is660nm, content is2%, the molar ratio of formaldehyde and urea is1.7and in this time the enthalpy is41.56J/g, breakage rate is16.1%, weight-loss ratio is0.4%.