【作者】 方明；

【导师】 杨玉良； 卢红斌；

【作者基本信息】 复旦大学 ， 高分子化学与物理， 2011， 博士

【摘要】 自2004年首次报道独立存在的石墨烯以来,它在力学、热学、电学、光学等方面的优异性能,使之迅速成为目前材料科学和凝聚态物理研究的一个热点,这归因于石墨烯的独特的二维晶体结构。本论文主要研究了石墨烯的制备、共价/非共价修饰及其初步应用。主要内容如下：1报道了通过重氮盐反应和原子转移自由基聚合(ATRP)相结合的方法实现了石墨烯的共价接枝。拉曼光谱(Raman)和红外光谱(FTIR)等手段证明了石墨烯和聚苯乙烯之间的共价键合。热失重分析(TGA)结果表明共价接枝在石墨烯表面的聚苯乙烯含量达到了82 wt%。由于石墨烯片层对聚苯乙烯链强烈的限制效应,DSC测试发现共价接枝在石墨烯表面的聚苯乙烯的玻璃化转变温度相对于自由的聚苯乙烯提高了15℃左右,这从侧面证明了石墨烯和聚苯乙烯之间的共价键合。而原子力显微镜(AFM)和透射电镜(TEM)为共价接枝提供了直观的证据：接枝在石墨烯片层表面的聚苯乙烯链的厚度大约为1 nm,并且片层中间区域的厚度比边缘区域更高。复合材料的杨氏模量和断裂强度随着接枝石墨烯含量的增加而提高,当添加量达到0.9 wt%的时候,其复合膜的杨氏模量和断裂强度分别增加了57.2%和69.5%。2.我们系统地调控了接枝在单层石墨烯表面的聚合物的接枝密度和聚合物的链长：通过控制重氮盐反应物的浓度,我们控制了聚合物在石墨烯表面的接枝密度；通过控制原子转移自由基聚合(ATRP)过程中的单体浓度,我们有效地调控了接枝在石墨烯表面的聚合物链长(Mn=21300～78900 g/mol)。TEM结果直观地显示了这些样品的不同表面形貌：低接枝密度的石墨烯表面聚苯乙烯的分布非常不均匀,而高接枝密度石墨烯表面聚苯乙烯分布非常均匀,并且随着分子量的增加,聚苯乙烯的分布变得越来越连续,直至在石墨烯表面形成了一层聚合物膜。DSC结果表明不同的接枝样品中,石墨烯对接枝聚苯乙烯链的限制情况也是不同的。同样,不同的接枝样品对复合材料热导率的影响也是有差异的：低接枝密度的石墨烯样品的增强效果优于高接枝密度的石墨烯样品,并且都比未经修饰的原料石墨和碳纳米管的增强效果要显著,这说明有效的界面结构控制对于提高复合材料的热性能是可行的。3.利用异氰酸酯和胺基的反应将环氧树脂的固化剂(芳香二胺,MDA)接枝到石墨烯的表面,制备了有机改性的石墨烯,然后通过固化反应将其交联到环氧树脂基体中。利用石墨烯表面的富胺基环境和位阻效应在环氧树脂中原位构筑了层次结构的中间相,它不仅有效地增强了在石墨烯和基体树脂间的载荷转移,而且增强了应力耗散能力。得到的复合材料具有很好的力学增强效果：含0.6 wt%石墨烯的复合材料,其抗弯曲强度增加了91.5%,而韧性增加了93.8%。这种方法有可能应用于发展轻质的、强韧聚合物纳米复合材料。4.通过简单的自主装方法制备了多功能的超疏水石墨烯/聚己基噻吩(P3HT)复合膜。扫描电子显微镜(SEM)和原子力显微镜(AFM)的结果显示了石墨烯/P3HT复合膜多尺度上的粗糙度：非溶剂(甲醇)的加入促进了聚己基噻吩链自发地沉积在石墨烯表面,形成了纳米尺度的粗糙度,同时不规则堆砌的石墨烯片层构成了微米尺度的粗糙度。得到的复合膜是多孔、轻质、环境稳定和良好的油水分离效率。其电导率达到了6500 Sm-1,这个值要比已报道的碳纳米管-聚合物超疏水膜的电导率高出很多,并且其比电磁屏蔽效率是固体铜的4倍。同时,我们也将这种协同自组装的方法使用到了超亲水蒙脱土(MMT)中,并成功地制备了具有超疏水功能的蒙脱土(MMT)/P3HT复合膜。5.通过简单的洗涤-抽滤相结合的方法制备了具有层状结构的氧化石墨(GO)/聚乙烯醇(PVA)复合膜。GO/PVA复合膜表现出了优异的力学性能：厚度为46μm的复合膜的断裂强度为276 MPa,断裂伸长率达到了9.2%,当用交联剂交联后,其力学性能得到了进一步的提高。并且GO/PVA复合膜具有pH响应特性,这在层状复合膜中属于首次报道。利用这个特性,我们成功地将Ag纳米颗粒负载在GO/PVA复合膜中,并发现我们制备的Ag-GO/PVA层状膜具有拉曼增强的功能。6.通过改变共价接枝在石墨烯表面的聚合物链长的方法来调控纳米颗粒在石墨烯表面的负载量和分布。接枝聚合物(PAA)对金属离子的锚固作用使纳米颗粒在石墨烯表面的生长动力学得到很好地控制,从而得到纳米颗粒尺寸分布较窄的样品。更多还原

【Abstract】 Graphene has attracted considerable attention from materials science and condensed matter physics due to its excellent mechanical, electric, thermal and optical properties. All of these can be attributed to its peculiar two-dimensional lattice structures. In this dissertation, we studied its preparation, functionalization and preliminary applications. The detailed results are summarized as follows:1. We firstly developed a new method to covalent functionalization of graphene by combining diazonium addition and atom transfer radical polymerization (ATRP). Raman spectra and FTIR spectra proved the existence of covalent bonds between graphene nanosheets and polystyrene (PS). TGA result shows that the PS content grafting on the surface of graphene nanosheets is about 82 wt%. Moreover, DSC result indicates that the glass transition temperature (Tg) of PS grafting on the grapheme surface is 15℃higher than that of free PS, which is related to the remarkable restriction effect of graphene nanosheets. Atomic force microscope (AFM) and transmission electron microscope (TEM) provided the direct evidence for covalent functionalization. The thickness of grafting PS layers on the grapheme surface is about 1 nm and furthermore, the thickness at the central area is higher than that at the peripheral area. The mechanical properties of nanocomposite films increase as increasing functionalized graphene contents. For the PS nanocomposite with 0.9 wt% graphene nanosheets, the Young modulus and strength at break respectively increase 57.2 and 69.5% relative to the pristine polymer.2. We covalently grafted PS chains onto the graphene surface, and systematically controlled their grafting density and PS chains length. By changing the concentration of diazonium salt, we controlled the grafting density; while by varying the concentration of monomer, we controlled the length of grafting PS chains (Mn=21300-78900 g/mol). TEM results show different surface morphologies of these samples. For the low density sample, the distribution of PS on the grapheme surface is not uniform, however, for high density sample the distribution of PS is rather uniform so that they formed a film on the grapheme surface. DSC results indicate that the restriction effect of graphene nanosheets on grafting PS chains is different. Heat conductivity measure demonstrates different influences of grapheme on the heat conductivity of composites. It was observed that the low grafting density graphene sample exhibited the better heat conduction than the high grafting density sample and furthermore, all functionalized graphene samples reveal better heat conductivities than those unfunctionalized raw graphite and carbon nanotube-filled composites. It is concluded that control of the interface structure is beneficial for optimizing the thermal properties of GN-based nanocomposites.3. Graphene nanosheets were organically modified with curing agent molecules (aromatic diamine, MDA), the functionalized graphene nanosheets were then covalently incorporated into the epoxy resin. We demonstrated an approach to in-situ construct hierarchical, flexible interphase structures in epoxy nanocomposites through a local amine rich environment around graphene nanosheets, by which the volume exclusion of grafting chains took effect. With the addition of 0.6 wt% amine-functionalized nanosheets, the resulting composite exhibits significant mechanical improvement,93.8 and 91.5% increases in fracture toughness and flecural strength, respectively. This approach affords a novel design strategy for developing high-performance composites.4. We prepared functional superhydrophobic films using a simple yet versatile solution deposition process that involves solubility-driven synergistic self-organization of graphene nanosheets and poly(3-hexylthiophene) (P3HT) chains. SEM and AFM results confirm the presence of the hierarchical surface roughness. The nanoscale roughness is caused by aggregation of P3HT while the micro-scale roughness is constructed by irregular stacking of graphene nanosheets. The resulting composite films are porous, lightweight, environmentally stable, and exhibiting excellent oil-water separation efficiency. They have electrical conductivities of over 6500 S m-1 and specific electromagnetic interference shielding effectiveness four times greater than solid copper. We also reveal that the synergistic self-organization approach presented here may be readily applied to other composite systems (montmorillonite), proving an industrially viable route to the fabrication of functional superhydrophobic films suited to practical applications.5. We prepared layered GO/PVA papers by a simple washing-filtration process and these layered papers exhibit excellent mechanical properties. For the paper with thickness of 46 mm, the elongation at break is up to 9.2%, accompanying with a mechanical strength of about 276 MPa. Furthermore, the mechanical properties were further improved after crosslinking. These GO/PVA papers are pH sensitive, which promoted the formation of Ag nanoparticles in the interlayered spacing of layered GO/PVA papers, revealing a strong surface enhanced Raman scattering (SERS) effect.6. we proposed a convenient method to modulate the loading and distribution uniformity of metal NPs on GNs by changing the length of polymer chains covalently grafted on GNs. The immobilization of functional groups (carboxyl groups) on polymer chains to metal ions allows the NPs on GNs to grow in a nearly similar kinetics, resulting in a narrow particle size distribution.更多还原