改性TiO_(2)纳米颗粒对相变微胶囊凝固特性的影响

Effect of surface-modified TiO_(2) nanoparticles on solidification of microencapsulated phase-change materials

使用十八烷基三甲氧基硅烷对二氧化钛(TiO_(2))纳米颗粒进行亲油改性处理;利用超声手段将改性TiO_(2)纳米颗粒加入十八烷(C18)中制备TiO_(2)-C18纳米悬浮液;采用微流控方法进一步获得结构规整、粒径均匀、成份可控的TiO_(2)-C18相变微胶囊。在此基础上,采用差示扫描量热仪、高低温交变湿热装置对TiO_(2)-C18相变微胶囊的凝固相变过程进行测试,重点研究了不同改性程度TiO_(2)纳米颗粒对相变微胶囊凝固过冷和冷/热循环稳定性的影响。结果证实通过控制硅烷偶联剂用量,能够实现对TiO_(2)纳米颗粒的亲油改性,使其能均匀分散于C18相变材料中,进而能够为晶核形成提供足够表面,达到消除相变微胶囊凝固过冷的目的,并同时保证TiO_(2)-C18相变微胶囊具有良好的循环稳定性。

Octadecyl trimethoxylsilane was used as silane coupling agent to improve the hydrophobicity of the titanium dioxide(TiO_(2))nanoparticles,and the resultant surface-modified TiO_(2) nanoparticles were dispersed into the n-octadecane(C18)by ultrasonic vibration.The obtained TiO_(2)-C18 nanofluids were then used to prepare the TiO_(2)-C18 microcapsules with regular spherical shape and uniform particle size distribution by a microfluidic method.The solidification behavior of the TiO_(2)-C18 microcapsules was measured by the differential scanning calorimeter and High and low temperature test apparatus,and the effect of surface-modified TiO_(2) nanoparticles on the supercooling degree and thermal cycling stability of the microencapules were studied.The results showed that hydrophobic TiO_(2) nanoparticles could be achieved by regulating the amount of silane coupling agent used.The modified TiO_(2) nanoparticles could be dispersed uniformly in the bulk of C18 and provided available surfaces to promote the heterogeneous nucleation.Consequently,the supercooling of TiO_(2)-C18 microcapsules could be eliminated completely,which also exhibited good thermal cycling stability.