【作者】 户华文；

【导师】 陈国华；

【作者基本信息】 华侨大学 ， 材料学， 2011， 硕士

【摘要】 本论文主要基于电化学氧化法制备改性纳米石墨及其聚合物基纳米复合材料,电化学氧化法是一种具有操作简便、产品后处理工序简单、能耗低以及环保性好的新型制备方法。这种电化学氧化作用能够在不同的电解条件下形成多种类型的功能化修饰纳米粒子,包括氧化程度的可控变化,而且各种不同氧化程度的改性微粒都能均匀稳定分散在水性介质中。一方面,高氧化程度的电化学改性纳米石墨粒子（EM-GNPs）能够用化学还原试剂处理,部分修复被破坏的石墨晶体结构,进而恢复部分导电性,导电率从还原前的（1.38±0.05）×10^-6 S/cm提升至还原后的（1.02±0.05）×10^-3 S/cm。而且还原后,石墨晶体002面的XRD特征衍射峰重新呈现出来。另一方面,EM-GNPs极性表面的亲水性还能通过有机阳离子表面活性剂进行改性处理,使其转变成亲油性。轻度电化学氧化改性的纳米石墨微片（EM-GNs）是在电解过程中产生的另一种纳米结构物质,具有极高的径厚比和良好的水分散性。它能够均匀分散在水溶性聚合物如聚乙烯醇（PVA）基体中,形成剥离型纳米复合膜。这种纳米复合膜较纯PVA在电、热和机械性能上都得到了改善。导电率从聚乙烯醇的绝缘体范围转变成复合材料的半导体范围,而导电渗滤阀值仅为6 wt.%左右。5 wt.% EM-GNs填充PVA复合材料的耐高温降解性提高了近45℃,玻璃化转变温度提高了近14℃。此外,机械拉伸强度和韧性也得到了协同增强。适度电化学氧化处理EM-GNPs能保留石墨晶体结构,同时引入含氧极性官能团和微量类氧化石墨晶体结构,从而EM-GNPs兼具了石墨极佳的面内性质和类氧化石墨特殊的表面性质,这将有利于制备出高性能环氧/EM-GNPs纳米复合材料。这种低氧化程度的EM-GNPs能够通过超声波辐射作用剥离分散到环氧基体中,平均粒子相对于分散前增大了1倍左右,这可能是因为组成EM-GNPs的微片层之间发生了移动,而又没有完全分离开。EM-GNPs在环氧基体中的这种特殊结构,决定了它能协同增强和增韧环氧基体。5 wt.% EM-GNPs填充环氧纳米复合材料的拉伸强度和断裂韧性分别提高了17 MPa和6 %。同时,耐高温降解性也有19℃的提升。更多还原

【Abstract】 In this thesis, the electrochemical oxidation method was mainly employed to produce electrochemically modified nano-graphite which was then compounded with polymer matrix to synthesize polymer based nanocomposites. This electrochemical oxidation method is facile, environmentally friendly, together with simple post-treatment of crude products and low energy cost. The electrochemical oxidation reaction will induce the formation of diverse functionalized nanoparticles, e.g., with variable extents of oxidation, under different electrolysis conditions. In addition, all of the electrochemically modified nano-graphite was well-dispersed in water medium. On one hand, the electrochemically modified nanoparticles （EM-GNPs） with high extent of oxidation were treated by a chemical reducer such as hydrazine and then reduced back to a certain amount of the starting graphitic crystalline structure, resulting in the partial restoration of the electrical conductivity, from （1.38±0.05）×10^-6 （before reduction） to （1.02±0.05）×10^-3 S/cm （after reduction）. Moreover, the characteristic X-ray diffraction peak of the 002 plane in graphitic crystal reoccurred after the reduction treatment of EM-GNPs. On the other hand, the hydrophilicity of EM-GNPs with polar surfaces was changed to lipophilicity by organic modification with a cationic surfactant such as dodecylamine.The electrochemically modified graphite nanosheet （EM-GN） with low oxidation extent was another type of nano-structure which possessed high aspect ratio and could be well-dispersed in water medium. EM-GNs were homogeneously and stably dispersed in a water-soluble macromolecule matrix such as poly（vinyl alcohol） （PVA） and formed an exfoliation type nanocomposite film. The properties of EM-GNs filled PVA nanocomposite films such as electrical, thermal, and mechanical properties were improved. The electrical conductivity was changed from an insulator to a semiconductor with a percolation threshold only about 6 wt.%; After compounding 5 wt.% loading of EM-GNs with PVA, the high temperature degradation resistance was improved by 45℃and glass transition temperature enhanced by 14℃, along with the improvement of the mechanical tensile properties including tensile strength and elongation toughness.Properly treating EM-GNPs by using electrochemical oxidation method retained graphitic crystal structure. Meanwhile, a certain amount of oxygen containing functional groups and a graphite oxide-like structure were generated in the EM-GNPs, leading to the excellent graphitic in-plane properties combined with the peculiar graphite oxide-like surface properties. This special structure of EM-GNPs was favorable to be used as a filler to produce high-performance epoxy nanocomposites. The EM-GNPs with low oxidation extent were well-dispersed into epoxy matrix under intense ultrasonic irradiation. The average diameter of the particles dispersed in the matrix doubled compared with the starting EM-GNPs, which was possibly due to the sliding effects between the ultra-thin sheets consisting of EM-GNPs, but without complete separation from each other. Due to the special structure of EM-GNPs dispersed in epoxy matrix, the synergistic reinforcing and toughening effects of GNPs on the epoxy were obtained. The tensile strength and toughness of the 5 wt.% EM-GNPs filled epoxy nanocomposites were improved by about 17 MPa and 6 %, respectively, along with ca. 19℃improvement of the high temperature degradation resistance.更多还原