【作者】 范金辰；

【导师】 印杰；

【作者基本信息】 上海交通大学 ， 高分子化学与物理， 2014， 博士

【摘要】 石墨烯是碳原子以sp2杂化轨道组成正六边形呈蜂巢状晶格的二维无机纳米片层材料。由于其独特的二维片层结构及优异的力学，热学，电学及光学的等性能，石墨烯在物理、化学、材料以及生物学等领域显示了重要的研究价值和广阔的应用前景。近几年来，石墨烯本征极高的机械强度，出色的导电和导热性能使其成为理想的纳米填料用于聚合物复合材料性能的增强和扩展。对于石墨烯材料的制备与改性，改善石墨烯在聚合物基体中的分散以及提高石墨烯与聚合物基体间界面相互作用一直是石墨烯/聚合物复合材料重要课题和研究热点。本学位论文主要围绕这些问题展开工作，创新性的运用多种方法实现石墨烯材料的制备以及功能化，拓展石墨烯在聚合物材料中的复合应用，具体研究内容及结果如下：(1)通过改性的Hummers法对石墨进行氧化得到氧化石墨，继而通过超声剥离制备了氧化石墨烯(Grapheneoxide,GO)。利用溶液共混和原位聚合法，首次将GO引入到海藻酸钠(Sodium alginate,SA)/聚丙烯酰胺(Polyacrylamide, PAM)双网络交联水凝胶中，得到GO/SA/PAM (GSP)的复合水凝胶。通过拉伸和压缩性能测试证明，GO的引入进一步显著提高了SA/PAM双网络交联水凝胶的机械性能。随着GO添加含量的增加，GSP的复合水凝胶的机械性能不断得到提高。GSP复合水凝胶不仅具有很高的机械性能，而且具有很好的弹性和韧性，在一定范围内压缩和拉伸后可以迅速恢复。同时，GO的引入使得GSP复合水凝胶也显示了很好的染料吸附性能。(2)以多壁碳纳米管(Multiwalled carbon nanotubes, MWNTs)为原料,通过高锰酸钾(KMnO4)和浓硫酸(H2SO4)纵向氧化切割MWNTs的内外壁，并结合超声剥离制备了氧化石墨烯纳米带(Unzipped Multiwalled Carbon Nanotubes Oxides, UMCNOs)。通过溶液共混流延成膜的方法将UMCNOs引入到壳聚糖(Chitosan, CS)基体中得到了UMCNOs/CS的复合材料。拉伸性能测试表明UMCNOs可以作为高效的纳米增强填料用于CS的机械性能增强。在UMCNOs添加含量仅为0.2wt%时，UMCNOs/CS复合膜的最大拉伸强度和杨氏模量分别达到了~142.7MPa,~6.9GPa。相比纯的CS膜，提高了约105.9%和165%。(3) UMCNOs作为纳米增强填料用于聚合物材料增强时，UMCNOs在相对较低填充含量下显示优越的增强效果，但是随着在聚合物基体中填充含量增加，UMCNOs在聚合物基体中非常容易产生团聚，限制了UMCNOs/聚合物复合材料机械性能的进一步提高。为了解决UMCNOs在复合材料增强中，相对低填充含量下易团聚的现象。我们有趣的发现，通过π-π共轭非共价作用将UMCNOs与MWNTs复合得到新颖的UMCNOs/MWNT(U/Ms)杂化材料，可以有效的改善UMCNOs在低填充含量下易团聚的现象。利用聚乙烯醇(Poly(vinyl alcohol)，PVA)作为模型聚合物，对比MWNTs-PVA，UMCNOs-PVA以及U/Ms-PVA复合膜在相同填料填充含量下的机械性能发现U/Ms-PVA复合膜的机械性能更加优异。在0.7wt%填充含量下，U/Ms-PVA的屈服强度和杨氏模量达到了145.8MPa和6.9GPa,大大高于MWNTs-PVA，UMCNOs-PVA的复合膜的机械性能。(4)利用二甲基亚砜(DMSO)和氢氧化钾(KOH)体系，通过去质子化的过程将宏观的凯夫拉纱线撕扯成宽度为30nm左右的对位芳纶纳米纤维(Aramidnanofiber,ANF)。通过π–π共轭作用，将ANF修饰固定到二维的石墨烯片层表面得到了ANF表面功能化的石墨烯杂化材料(ANF-functionalized graphene nanosheets, ANFGS)用于聚合物复合材料机械性能的增强填料。通过溶液共混流延成膜的方法将ANFGS与聚甲基丙烯酸甲酯(PMMA)复合制备得到了ANFGS/PMMA复合膜。ANF的引入改善了石墨烯在聚合基体中的分散效果，并大大提高了石墨烯与聚合物基体间界面作用力。拉伸测试结果发现在ANFGS填充含量仅为0.1wt%时，ANFGS/PMMA复合膜的拉伸强度达到了46.5MPa,相比纯的PMMA膜的拉伸强度提高了近35.9%。ANFGS/PMMA复合膜的拉伸强度和杨氏模量随着ANFGS填充含量的增大而增大，在0.7wt%时，ANFGS/PMMA复合膜的拉伸强度和杨氏模量达到最大，为63.1MPa和3.4GPa。另外，由于ANF的紫外吸收性能，ANFGS/PMMA复合膜展现了一定紫外光屏蔽效果。(5)基于液相直接剥离石墨制备石墨烯的方法，利用阿拉伯胶(Gum arabic, GA)开辟了一种新颖绿色简单的方法制备银纳米粒子/石墨烯杂化材料。通过将原始的石墨粉加入到GA水溶液中超声剥离石墨后得到了GA表面改性的石墨烯片层(GA-functionalizedgraphene nanosheets, GA-G)。当石墨粉和GA初始浓度在140和100mg/mL时，通过8小时的超声，石墨烯的浓度最大可以达到0.69mg/mL。对得到的GA-G片层进行统计分析，得出GA-G片层面积和厚度主要集中在0.5-2μm2和2-6nm。很巧妙的是，GA-G表面吸附的GA可以被用来原位还原固定银纳米粒子，于此制备得到了表面银纳米粒子均一，规整的Ag/GA-G二维片层杂化材料。通过GA直接剥离和还原制备的Ag/GA-G的杂化材料可以作为一种高效的表面增强拉曼光谱(Surface-enhanced Raman spectroscopy, SERS)的底物，在液相环境中对4-氨基苯硫酚(4-aminothiophenol,4-ATP)探针分子的检测效果可以达到10-6M。(6)利用甲基丙烯酸缩水甘油酯(Glycidyl methacrylate, GMA)对GA进行化学改性，通过环氧开环以及酯交换两个过程得到GMA改性的GA(GMA-GA)。GMA-GA同样可以用于石墨的液相剥离和分散，相比于原来的GA来说，剥离效率明显提高。同时GMA-GA结构中带有乙烯基双键的分子链段，利用GMA-GA直接液相剥离分散的方法得到了GMA-GA功能化的石墨烯片层(GMGS)。通过原位聚合的方法将GMGS作为水凝胶的机械增强填料引入到聚丙烯酸(PAA)水凝胶结构中，大大改善了PAA水凝胶的机械性能。更多还原

【Abstract】 Graphene is a single layer graphite sheet that consisting of sp2carbonatoms covalently bonded in honeycomb crystal lattice. Due to itsfascinating properties such as giant electron mobility, high thermalconductivity and high thermal stability, graphene has aroused considerableresearch interest and exhibited broad application prospect in physics,chemistry, materials and biology, etc. Recently, owing to its intrinsicexcellent mechanical strength, large surface area, electric and thermalconductivities, graphene nanosheets are widely used as ideal nanofillers forenhancing and extending the properties in polymer composites. However,for graphene-based composite materials, there are some main problemsstill waiting for resolve in its application of academia and industry, e.g.,preparation and functionalization of graphene, improving the dispersibilityof graphene and its derivative in polymer matrices, and enhancing interfaceinteraction between graphene nanosheets and polymer matrix. Therefore,we carried the research works around these above problems. In thisdissertation, we innovative utilized various implementation methods forpreparation and functionalization of graphene and further realized andexpanded the composite applications of graphene in composite materials.The details of research works are as follows:(1) Using a modified Hummers method, graphite oxide was obtained byoxidation of graphite. It can be exfoliated into graphene oxide (GO)nanosheets and formed uniform and stable GO aqueous dispersion with sonication. Through free-radical polymerization of acrylamide (AAm) andSA in the presence of GO in aqueous system followed with ionicallycrosslinking of calcium ions, a novel graphene oxide (GO)/sodium alginate(SA)/polyacrylamide (PAM)(GSP) ternary nanocomposite hydrogel withexcellent mechanical performance have been fabricated. As-preparedGO/SA/PAM (weight ratio SA/AAm=1/2) ternary nanocompositehydrogel with5wt%of GO displays a compressive stress as high as1.543MPa at the compressive deformation of70%. The tensile strength andmodulus of the hydrogel achieved~201.7and~30.8kPa, respectively.Meantime, the GSP nanocomposite hydrogels can recover a largeproportion of elongation at break and exhibit the good elasticity.Additionally, the GSP ternary nanocomposite hydrogel exhibitedgood adsorption properties for water-soluble dyes.(2) Multiwalled carbon nanotubes (MWNTs) have been widely used asnanofillers for polymer reinforcement. However, it has been restricted bythe limited available interface area of MWNTs in the polymer matrices.Oxidation unzipping of MWNTs is an effective way to solve this problem.Unzipped multiwalled carbon nanotube oxides (UMCNOs) obtained byoxidation unzipping MWNTs were used as novel nanofillers formechanical reinforcement of chitosan (CS) matrix. The UMCNOs/CSnanocomposite films with different amounts of UMCNOs were fabricatedby solution-casting the mixtures of UMCNOs and CS acetic acid aqueousdispersions. The structures and mechanical properties of thenanocomposite films were characterized by XRD, FT-IR, SEM, and tensiletests. The results demonstrated that Compared to neat chitosan, theUMCNOs/CS nanocomposite films showed~105.9%increase in tensilestrength from69.3to142.7MPa, and~165.3%increase in Young’s modulus from2.6to6.9GPa with incorporation of only0.2wt%ofUMCNOs into the chitosan matrix.(3) The unzipped multiwalled carbon nanotube oxides (UMCNOs)exhibit excellent enhancement effect with low weight fractions, butagglomeration of UMCNOs at a relatively higher loading still hamperedthe mechanical reinforcement of polymer composites. We interestinglyfound that the dispersion of UMCNOs in polymer matrices can besignificantly improved with the combination of pristine MWNTs. Thehybrids of MWNTs and UMCNOs (U/Ms) can be easily obtained byadding the pristine MWNTs into the UMCNOs aqueous dispersionfollowed with sonication. With π-stacking interaction, the UMCNOs wereattached onto outwalls of MWNTs. The mechanical testing of the resultantpoly (vinyl alcohol)-based composites demonstrated that the U/Ms can beused as ideal reinforcing fillers. Compared to poly (vinyl alcohol)(PVA),the yield strength and Young’s modulus of U/Ms-PVA composites with aloading of0.7wt%of the U/Ms approached~145.8MPa and6.9GPa,which are increases of~107.4%and~122.5%, respectively. Thereinforcement effect of U/Ms is superior to the individual UMCNOs andMWNTs due to the synergistic interaction of UMCNOs and MWNTs.(4) The bulk aramid macroscale fibers can be effectively split intoaramid nanofibers (ANFs) in dissolution of dimethylsulfoxide (DMSO)with the presence of potassium hydroxide (KOH). We first introduced theANFs into the structure of graphene nanosheets through noncovalentfunctionalization with π-π stacking interaction. Aramid nanofibersfunctionalized graphene sheets (ANFGS) were successfully obtained byadding the graphene oxide (GO)/DMSO dispersion into the ANFs/DMSOsolution followed with the reduction of hydrazine hydrate. Combining the two ultra-strong materials, ANFs and graphene nanosheets (GS), theANFGS can be acted as novel nanofillers for polymer reinforcement.ANFGS can be used as ideal nanofillers for reinforcing the mechanicalproperties of poly (methyl methacrylate)(PMMA). With loading of0.7wt%of ANFGS, the tensile strength and Young’s modulus of ANFGS/PMMAcomposite film approached63.2MPa and3.42GPa, increased by~84.5%and~70.6%respectively. The thermal stabilities of ANFGS/PMMAcomposite films were improved with addition of ANFGS. Additionally, thetransparencies of ANFGS/PMMA composite films have a certain degreeof UV-shielding effect due to the ultraviolet light absorption of ANFs inANFGS.(5) Based on the method of direct liquid-phase graphene exfoliation，we present a green and facile way for preparing graphene–Ag nanohybridsassisted with gum arabic (GA). GA functionalized graphene sheets (GA-G) were prepared by directly exfoliating graphite flakes in the gum arabic(GA) aqueous solution with sonication. After sonication for8h, the CGScan run up to0.69mg mL-1with the initial graphite concentration of140mg/mL and GA concentration of100mg mL-1. The distributions of thelateral dimensions and thickness for graphene flakes were mainlyconcentrated at the range of0.5-2μm2and2-6nm, respectively. The silverions can be directly reduced and immobilized on the surface of GA-Gnanosheets by GA. The Ag/GA-G hybrid materials can be used as suitablesubstrates of surface-enhanced Raman spectroscopy (SERS) for detectionof4-aminothiophenol (4-ATP) at detectable level of concentration of10-6M in aqueous environment.(6) Glycidyl methacrylate-modified gum arabic (GMA-GA) wasobtained by chemically modification of gum arabic (GA) with glycidyl methacrylate (GMA). Through two different pathway reactions, epoxyring-opening and transesterification, the vinyl groups of C=C coming fromGMA were coupled onto the polysaccharide structure of GA. Aftermodification, the GMA-GA can still be used for liquid-phase directexfoliation of graphite. With assist of GMA-GA, the maximumconcentration of graphene flakes can reach~1.12mg/mL. Using thistechnique, GMGS can be easily obtained by centrifugal separation aftersonication. The functionalized graphene flakes, coupled with vinyl groupscoming from the GMA-GA were introduced into poly (acrylic acid)(PAA)hydrogel through in situ polymerization for enhancing the mechanicalproperty of hydrogels. Compared to PAA hydrogel, the compressivestrength and elastic modulus of GMGS/PAA composite hydrogel with5wt%of functionalized graphene flakes reach~49.2and~66.9kPa, increasedby~846.1%and~243.7%, respectively.更多还原