【作者】 李文娟；

【导师】 于中振；

【作者基本信息】 北京化工大学 ， 材料科学与工程， 2012， 硕士

【摘要】 石墨烯（graphene）具有优异的导电性能，石墨烯作为导电纳米复合材料的填料在近些年来成为复合材料的研究热点。然而，石墨烯规模化制备困难和在极性聚合物基体中容易团聚的问题成为制备性能优异的复合材料所面临的主要挑战。在强酸强氧化剂的条件下通过化学氧化法制备的氧化石墨烯（graphene oxide, GO）通常可以视为石墨烯的前躯体，在经过化学还原或者热还原的方法消去除氧化石墨烯表面接枝的含氧官能团成为批量化生产石墨烯的有效方法。而在将氧化石墨烯还原为石墨烯的同时进行表面功能化修饰能促进其在聚合物基体中分散，由于氧化石墨烯表面存在着大量的羟基、羧基和环氧基等含氧官能团，这为氧化石墨烯的表面功能化修饰提供了反应点。本论文中，我们介绍了一种不添加传统的化学还原剂，只加入十八烷基胺（octadecylamine,ODA）就能对氧化石墨烯进行功能化及还原的简单有效的方法。我们利用氧化石墨烯上面的含氧官能团与十八烷基胺之间的亲核取代反应，将长碳链的烷基胺以共价键的方式接枝在氧化石墨烯片上，并将其作为聚苯乙烯(PS)的填料，制得了导电纳米复合材料。研究发现：经过十八烷基胺修饰的氧化石墨烯，材料表面由亲水性转变为亲油性，有利于其在非极性聚合物中的分散；在采用回流的方法制备化学修饰的氧化石墨烯时，十八烷基胺不仅在氧化石墨烯片层间实现了有效的插层，多种表征手段表明氧化石墨得到了有效的还原；同时被十八烷基胺修饰且还原过的石墨烯的电导率提高了3个数量级；为了研究复合材料制备过程中温度对电导率的影响，本实验对氧化石墨烯和修饰产物（氧化石墨烯-十八烷基胺（GO-ODA））分别在聚合物加工温度下进行热处理，测试结果证实它们的电导率得到了进一步的提高；在制备的PS/GO-ODA复合材料中，填料GO-ODA与PS基体表现出良好的相容性，在聚合物中得到有效的剥离，从而形成良好的导电网络；相对于PS/GO复合材料，PS/GO-ODA复合材料的导电率明显提高（渗流阈值为0.45vol.%），特别是在填料GO-ODA的体积分数为0.92vol.%时复合材料的电导率高达0.4638S/m。其次，我们对十八烷基胺及酸碱性对氧化石墨烯的还原及修饰进行了研究，研究发现，在没有十八烷基胺参与反应的条件下，氧化石墨烯在90℃的碱性条件下回流约3小时会被还原，而不调节pH值时，氧化石墨烯在90℃下回流20小时，氧化石墨烯仍不会被还原；在不调节pH值的前提下，十八烷基胺与氧化石墨烯在25oC混合搅拌20小时，GO只会被插层而并无明显的还原，在90℃回流20小时，GO既被插层又被还原,在90℃下，调节pH值至强碱性能加快十八胺对氧化石墨烯的还原速度，而将pH值调节至强酸性时，十八胺对氧化石墨烯没有还原效果。上述研究结果说明温度和碱性环境是影响还原氧化石墨烯的关键因素，也就是说在还原过程中，十八烷基胺为氧化石墨烯的还原提供了碱性环境，氧化石墨烯在碱性环境中高温回流才得到了还原，除此之外，十八烷基胺在此过程中还担当了插层剂的作用，显著增大了原有氧化石墨的层间距。此外，我们研究了不同长碳链的烷基胺对氧化石墨烯的作用。结果发现：不同长碳链的烷基胺均能对氧化石墨烯起到插层及还原的作用；短碳链的烷基胺更容易进入到氧化石墨烯的层间，与其上面的基团反应，接枝率较高，而长碳链的烷基胺因其具有较长的碳链，插层效果显著，就是说随着碳链的增长，插层效果越明显，层间距越大；碳链越短，接枝上的分子链越多。本课题的创新点在于寻找到了一种既能对氧化石墨烯进行插层，改变其极性，又能对其进行还原的表面修饰剂，得到的填料能够在聚苯乙烯基体中形成良好的导电通路，制得了低填料含量高导电率的纳米复合材料。更多还原

【Abstract】 Graphene has excellent electrical property, as the filler for conductivecomposites, has become the hot topic in recent years. However, it’s toodifficult to produce graphene in large-scale, and graphene will aggregateeasily in polar polymer matrix, which become the challengement to preparecomposite with excellent properity. As a precursor of graphene, grapheneoxide (GO) can be easily reduced to graphene by chemical or thermalapproaches, which is the effective method to prepare graphene in large scale.Simultaneously reducing and modifying the surface of GO can improves thedispersion in polymer. The plentiful oxygen-containing groups on GO provideactive sites for chemical modification of GO surface.In this paper, we demonstrate an efficient approach to functionalize and insitu reduce GO with octadecylamine （ODA） without the addition ofconventional chemical reducing agents. The presence of the long octadecylchain made the hydrophilic GO hydrophobic, evidenced by the selectivedispersion of the ODA-functionalized GO (GO-ODA) in chloroform solventrather than in water. Interestingly, different from the insulating GO, GO-ODAbecame electrically conductive due to the reduction in the presence of ODA.The electrical conductivity of GO-ODA was further increased by incidentalthermal reduction during the compression-molding of its polystyrene (PS)composites at210oC, which exhibited a sharp transition from electricallyinsulating to conducting with a low percolation threshold (0.45vol.%). Thehigh conductivity of the PS/GO-ODA composites is attributed to the improveddispersion and the reduction of GO-ODA in comparison with GO.Further, we study the reduction effect of GO with the ODA in different pHvalue, we found that GO can be reduced by refluxing3hours at90oC underalkalinity condition without ODA, but GO can not be reduced without ODAand without changing pH value even by refluxing20hours at90oC. When GOwas stirring with ODA for20hours at25oC on condition that pH value is notchanged, GO was intercalated and with no obvious reduction effect, but whenthe temperature becomes90oC, GO is intercalated and reduced simultaneously, and when we change the pH value into the alkalinity, the speed of reductionwill be accelerated, while under acid condition, GO is just intercalated but hasno obvious reduction. The above results demonstrate that the temperature andenvironment with different pH value are the critical factor of the redution, inother word, ODA provides the alkalinity condition for reducing GO, GO canbe reduced by refluxing at high temperature under alkalinity condition, inaddition, ODA undertake the intercalation agent during the procss, whichincrease the interlamellar spacing remarkably.At last, we study the effect of GO by refluxing with alkylamine ofdifferent long alkyl chains. We find the alkylamine with alkyl chains ofdifferent length have the reduction effect to GO, alkylamine with short alkylchains is more easily to get into the layer space, and the rate of grafting ishigher, alkylamine with long alkyl chains mades better effect of intercalation.That is to say, intercalation effect will be more obvious along with the increaseof alkyl chains length, and the layer space will be wider, while shorter alkylchains, molecular chains grafted to GO will be more.Innovative point of this paper is to find a surface modifier to intercalateGO, change polar of GO and reduce GO, the filler obtained by this methodcan disperse in polystyrene and form the network for electrical conductivity,and finaly, an excellent conductive nanocomposite with low content of fillerwill be obtained.更多还原