【作者】 万晶晶；

【导师】 郭宝春；

【作者基本信息】 华南理工大学 ， 材料学， 2010， 硕士

【摘要】 复合型导电高分子材料由于保留了高分子的优良加工特性、质量轻、电阻率范围可调及成本低廉等特点,在光电子器件、信息、传感器、电磁屏蔽等领域有着广泛诱人的应用前景,从而具有重要的研究意义和实际价值。石墨烯具有独特的导电性和导热性,其与聚合物组成的复合材料具有优良的导电性质、导热性能和力学性能,具有重要的研究意义。但是,为了获得具有优异性能的复合型导电高分子,必须将石墨剥离成石墨烯并在聚合物中获得良好的分散。本研究为了获得具有优异导电性能的复合型导电高分子,在如下两方面进行了研究:(1)离子液体与石墨烯存在潜在的相互作用,同时离子液体本身具有导电性质且化学性质稳定,因此,可望与石墨复合改性高分子材料以获得高性能的复合材料。本部分研究选择环氧树脂为聚合物基体,研究了离子液体及石墨对环氧树脂固化行为的影响,从而为这类材料的性能优化提供技术基础。主要得到的结论如下:在低含量膨胀石墨(EG)体系中,活化能(Eα)在凝胶点前比纯环氧树脂体系要低;但EG含量相对较高时,其Eα反而比纯环氧树脂体系的Eα高。在含有[BMIm]PF6的体系中,[BMIm]PF6和Jeffamine之间易形成氢键,从而降低Jeffamine胺基的反应活性,使Eα随着转化率的增加而增大。研究还发现,[BMIm]PF6咪唑阳离子和EG之间存在特殊相互作用,有助于石墨微片在环氧树脂中的分散。同时,分散良好的石墨微片对[BMIm]PF6形成屏蔽作用,从而抑制[BMIm]PF6和Jeffamine之间氢键的形成,导致Eα比只含有[BMIm]PF6的体系低。(2)通过化学氧化法可制备聚合物/石墨烯导电复合材料,但是在制备过程中由于石墨烯的π-π相互作用很容易聚集,从而出现还原石墨的二次团聚,为了克服这一问题,本部分研究采用羟丙基纤维素(HPC)为基体,利用其最低临界溶解温度行为(LCST)有效阻止了氧化石墨烯在还原过程中的团聚。同时,基于第一部分研究证实的石墨烯-离子液体相互作用,在HPC/石墨烯导电复合材料体系中引入离子液体进一步改善复合材料的导电性能,获得了性能优异的HPC/石墨烯/离子液体复合材料。主要得到的结论如下:超声处理可以将氧化石墨烯剥离为仅1~2层厚度的石墨烯片层,从而在HPC溶液中形成稳定均一的分散体系。离子液体[BMIm]Cl可以显著提高复合材料的电导率:在相同RGO含量下,20phr [BMIm]Cl可以将材料电导率提高2~3个数量级。当石墨烯体积分数为0.57%时,其电导率可达5.66×10-4 S/m;当RGO含量增加到10.45 vol%时,其电导率高达10.5 S/m。同时,研究表明石墨烯可以有效地抑制HPC的结晶,而且随着RGO含量的增加,HPC结晶相(2θ=8.2o)对应的衍射强度会逐渐减弱。此外,在添加20phr [BMIm]PF6的样品中,HPC的结晶相被破坏程度最高。更多还原

【Abstract】 Owing to retaining excellent processing characteristics of polymer, light weight, adjustable resistance and low cost, conductive polymer based composites have attractive prospects in such applications as optoelectronic devices, information, sensors, electromagnetic shielding and so on. Consequently, the research of conductive polymer based composites has important practical value. Graphene has a unique electrical conductivity and thermal conductivity. Composites filled with graphene have extraordinary conductivity and mechanical properties, so the study on graphene-polymer composites is of scientific importance. Both delaminating graphite into single graphene and dispersing uniformly the graphene into polymer matrix are crucial to the realization the potential performance of the conductive composites. In this study, in order to obtain composites with excellent conductive properties, the following two aspects were researched.(1) Due to the presence of potential interaction between ionic liquids and graphene and the attractive characteristics of the ionic liquids such as conductity and stable chemical properties, it is expected that the combination of graphene and ionic liquid will render better conductive performance to the polymer composites. In this part, we chose epoxy resin as the matrix of the composite, the effects of the ionic liquids and graphite on the curing behavior of epoxy resin were discolosed. These results provided technical basis for optimizing the performance of such materials. Mainly conclusions were illustrated as follows.At lower concertration of eapanded graphite (EG), compared with the curing activation energy (Eα) of the neat epoxy resin, the composite with EG has a lower Eαbefore the gelation, but a higher Eαafter the gelation. However, at higher concertrations of EG, in the whole conversion range, the composite with EG shows a higher Eαcompared with the neat epoxy resin. Besides, as the curing proceeded, a peculiar increase of Eαis found in systems containing [BMIm]PF6. Due to the formation of hydrogen bonding between [BMIm]PF6 and the harder (Jeffamine),the reactivity of Jeffamine is considerably decreased, leading to a much higher Eαin [BMIm]PF6-containing systems, especially at higher conversion. In systems containing a combination of [BMIm]PF6 and EG, due to the unique interactions between EG and [BMIm]PF6, the shielding effect provided by the well-dispersed EG sheets constrains the formation of hydeogen bonding between [BMIm]PF6 and Jeffamine, leading to lowered Eαcompared with that for the system containing [BMIm]PF6 only.(2) Conductive polymer/graphene composites could be prepared by chemical oxidation and reduction process. However, during the reduction process, graphene is easy to stack together because ofπ-πinteraction. In order to overcome this problem, we chose hydropropyl cellouse (HPC) as the matrix for its low critical solution temperature (LCST) behavior. The reduction of oxidized graphene above LCST could effectively prevent the reuniting of the graphene into stacked structure. Meanwhile, based on the confirmed interaction between graphene and ionic liquids in the first part, incorporation of ionic liquids into the HPC/graphene systems further improved the conductivity of composites. The main results were concluded as follows.Oxidized graphene can be delaminated into only 1~2 layers via ultrasound treatment, which can form a stable and uniform dispersion in the HPC. [BMIm]Cl can significantly improve the electrical conductivity of composites. Under the same content of reduced graphite oxide (RGO), the conductivity of composite can be increased by 2~3 orders of magnitude with the help of 20 phr [BMIm]Cl. When the volume fraction of graphene was only 0.57%, the conductivity of composite reached 5.66×10-4 S/ m, while the content of RGO increased to 10.45 vol%, its electrical conductivity reached up to as high as 10.5 S/m. Besides, it was showed that graphene can effectively restrain the crystallization of HPC, and the corresponding diffraction intensity of crystalline phase (2θ= 8.2o) gradually decreased along with the increasing of the content of RGO. The crystallization of HPC was further suppressed when 20 phr of [BMIm] PF6 was included.更多还原