复合碳纳米管流体的合成及其稳定性和导热强化机理研究

发布时间：2018-01-30 23:37

本文关键词： 复合碳纳米管纳米流体悬浮稳定性导热率　出处：《武汉理工大学》2015年硕士论文　论文类型：学位论文

【摘要】：碳纳米管具有质轻、导热性高等优点,由其制备的纳米流体是一类新型强化传热流体,在材料、机械、电子等等领域具有巨大的应用前景。目前,阻碍碳纳米管纳米流体工程应用的重大瓶颈之一是碳纳米管与基液相容性差、难以分散成均匀悬浮液,产生团聚、沉淀,堵塞流通管道。因此,研究提高碳纳米管流体的稳定性和导热率的工艺和机理,具有重要理论意义和应用价值。本文针对碳纳米管与基液乙二醇(EG)相容性差,悬浮稳定性差的问题,探索了一种通过在碳纳米管的表面接枝聚乙二醇支链,合成复合碳纳米管的新方法。首先,通过配制浓硫酸与浓硝酸混合溶液处理碳纳米管,制备表面功能化碳纳米管;然后,通过在表面功能化碳纳米管表面接枝聚乙二醇,得到复合碳纳米管。并采用红外光谱,扫描电镜,热重分析,XRD,比表面积和元素分析等等手段对复合碳纳米管表面结构,表面性质,表面接枝有机物含量,晶型,比表面积及元素种类等进行表征。实验结果表明:碳纳米管表面成功接枝了聚乙二醇分子,其接枝量大于20%,粒径增大约5-10nm。并且,通过表面接枝没有改变碳纳米管的晶体结构。以合成的聚乙二醇原位接枝改性的复合碳纳米管和乙二醇为原料,制备了乙二醇基复合碳纳米管流体。采用荧光显微镜,观察到复合碳纳米管能够较好地分散在基液乙二醇中;采用旋转流变仪分析其流变特性;采用导热率测试仪测试其导热率和稳定性。实验结果表明:复合碳纳米管纳米流体的稳定性和导热率得到显著增强。其导热率增强率随体积分数的增加而升高,并且随温度升高而显著提高,粘度随温度升高而明显降低。分析复合碳纳米管纳米流体的稳定性和导热率增强的机理,其中最重要的机制是碳纳米管表面接枝聚乙二醇后,赋予碳纳米管表面与基液乙二醇相同的分子结构,碳纳米管表面接枝的聚乙二醇支链可以与基液乙二醇相容,并伸展到基液乙二醇中,从而提高了碳纳米管和基液的分散稳定性,并且减少了团聚和缠绕,因此,碳纳米管在基液乙二醇中的布朗运动就更快,导致导热率升高。
[Abstract]:Carbon nanotubes (CNTs) have the advantages of light weight and high thermal conductivity. The nanofluids prepared by CNTs are a new type of enhanced heat transfer fluids, which have great application prospects in the fields of materials, machinery, electronics and so on. One of the major bottlenecks hindering the engineering application of CNTs is the poor compatibility between CNTs and the base solution, which makes it difficult to disperse into uniform suspensions, to produce agglomeration, to precipitate, and to block the flow pipes. It is of great theoretical significance and practical value to study the process and mechanism of improving the stability and thermal conductivity of carbon nanotubes. In this paper, the compatibility of carbon nanotubes with ethylene glycol (EGG) is poor. A new method of synthesizing composite carbon nanotubes by grafting polyethylene glycol branched chain onto the surface of carbon nanotubes was explored. Surface functionalized carbon nanotubes were prepared by preparing concentrated sulfuric acid and concentrated nitric acid mixed solution to treat carbon nanotubes. Then, the composite carbon nanotubes were prepared by grafting polyethylene glycol onto the surface of the functionalized carbon nanotubes, and were characterized by infrared spectroscopy, scanning electron microscope and thermogravimetric analysis (TGA). Specific surface area and elemental analysis were used to analyze the surface structure, surface properties, surface grafted organic content and crystal form of composite carbon nanotubes (CNTs). The experimental results showed that the surface of carbon nanotubes was grafted with polyethylene glycol, the grafting amount was more than 20 and the particle size increased about 5-10 nm. The crystal structure of carbon nanotubes was not changed by surface grafting. The composite carbon nanotubes and ethylene glycol modified by in situ grafting of polyethylene glycol were used as raw materials. The ethylene glycol based composite carbon nanotube fluid was prepared and the fluorescence microscope was used to observe that the composite carbon nanotube could be dispersed in the base liquid ethylene glycol. The rheological characteristics were analyzed by rotating rheometer. The thermal conductivity and stability of composite carbon nanotube nanofluids were measured by thermal conductivity tester. The results showed that the stability and thermal conductivity of composite carbon nanotube nanofluids were significantly enhanced, and the enhancement rate of thermal conductivity increased with the increase of volume fraction. The stability and thermal conductivity of composite carbon nanotube nanofluids were analyzed. The most important mechanism is that the surface of carbon nanotubes is grafted with polyethylene glycol and the surface of carbon nanotubes is endowed with the same molecular structure as the base liquid ethylene glycol. The branched polyethylene glycol chains grafted on the surface of carbon nanotubes can be compatible with the base liquid ethylene glycol and extend to the base liquid ethylene glycol, thus improving the dispersion stability of carbon nanotubes and the base solution, and reducing the agglomeration and winding. The Brownian motion of carbon nanotubes in the base liquid ethylene glycol is faster, resulting in higher thermal conductivity.
【学位授予单位】：武汉理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ127.11;TB383.1

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