碳纳米管纳米复合材料的研究现状及问题Status of carbon nanotubes nanocomposites research and issues
Since 1991 Tsukuba, Japan, NEC Laboratories physicist Sumio Iijima (Sumio Iijima) [1] first reported the nanotubes since its unique atomic structure and properties of great interest to scientists . Different layers of graphite nanotubes can be divided into single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs). Carbon nanotubes have a high specific surface area , mechanical properties ( axial carbon nanotubes theoretically elastic modulus and tensile strength were 1 ~ 2 TPa and 200Gpa), excellent thermal properties and electrical properties ( carbon nanotubes heat up to a temperature under vacuum 2800 ℃, is two times the thermal conductivity of diamond , the electron carrier capacity is 1000 times that of copper wire ) [ 2-7 ] . These features make carbon nanotubes in composite materials ideal filler. Can be easily processed into a polymeric structure of complex components manufactured using conventional processing methods to the polymer / carbon nanotube composite materials processing and manufacturing into a complicated structure member, and in the process will not damage the carbon nanotubes structure , thereby reducing production costs. Accordingly, the polymer / carbon nanotube composites have been extensively studied .
自从 1991 年日本筑波 NEC 实验室的物理学家饭岛澄男(Sumio Iijima)[1]首次报道了碳纳米管以来，其独特的原子结构与性能引起了科学工作者的极大兴趣。按石墨层数的不同碳纳米管可以 分 为单壁碳 纳 米管(SWNTs) 和多壁碳 纳 米管(MWNTs)。碳纳米管具有极高的比表面积、力学性能(碳纳米管理论上的轴向弹性模量与抗张强度分别为 1~2 TPa 和 200Gpa)、卓越的热性能与电性能(碳纳米管在真空下的耐热温度可达 2800 ℃，导热率是金刚石的 2 倍，电子载流容量是铜导线的 1000 倍)[2-7]。http://www.ukthesis.org/wlglzy/
Depending on the application purpose , the polymer / carbon nanotube composites can be correspondingly divided into structural and functional composite material composite of the two categories. In recent years , people have prepared various polymer / carbon nanotube composites , and other properties of various mechanical properties, electrical properties, thermal properties , optical properties of the prepared composites were extensively study results of these studies show that : properties of the polymer / carbon nanotube composites depends on various factors such as the type of carbon nanotubes ( single- wall carbon nanotubes or multi- walled carbon nanotubes ) , the shape and structure ( diameter length and chiral ) and the like. This paper mainly research status of polymer / carbon nanotube composites were reviewed, and discussed the challenges they face .
根据不同的应用目的，聚合物/碳纳米管复合材料可相应地分为结构复合材料和功能复合材料两大类。近几年，人们已经制备了各种各样的聚合物/碳纳米管复合材料，并对所制备的复合材料的力学性能、电性能、热性能、光性能等其它各种性能进行了广泛地研究，对这些研究结果分析表明：聚合物/碳纳米管复合材料的性能取决于多种因素，如碳纳米管的类型(单壁碳纳米管或多壁碳纳米管)，形态和结构(直径、长度和手性)等。
1 Preparation of a polymer / carbon nanotube composites
聚合物/碳纳米管复合材料的制备
Polymer / carbon nanotube composite material are mainly three types: liquid blend , solid phase communion and in-situ polymerization method , in which the blending method is more common.
1.1 composite solution blending method
Solution method is the use of mechanical stirring , magnetic stirring or ultrasonic energy to peel open nanotube aggregates uniformly dispersed in the polymer solution , excess solvent is then obtained after removal of polymer / carbon nanotube composites . The advantage of this method is simple, convenient, mainly used for the preparation of membrane material . Xu et al [8] and Lau et al. [9] were prepared using this method CNT / epoxy composites , and the reported properties of the composites . In addition to the epoxy resin , other polymers ( such as polystyrene , polyvinyl alcohol and polyvinyl chloride, etc. ) may also be a composite material prepared in this way .
1.2 melt blending complex method
Melt blending method is applied to the rotor via a shearing force dispersing the carbon nanotubes in the polymer melt . This method is particularly suitable for the preparation of thermoplastic polymer / carbon nanotube composites . The main advantage of this method is to avoid solvent or surfactant contamination of composite materials , composites found no fracture and damage, but only for high temperature, difficult to break down the polymer. Jin et al. [10] This was prepared using the PMMA / MWNT composite materials , and to study their properties. The results show that the carbon nanotubes are uniformly dispersed in the polymer matrix , there is no obvious damage. Significantly increase the storage modulus composites.
1.3 In situ composite method
Carbon nanotubes dispersed in a polymer of monomer , initiator , causing the monomer in-situ polymerization of the polymer to obtain a polymer / carbon nanotube composites. This approach is considered to improve the dispersion of carbon nanotubes and most effective way to strengthen its polymer matrix interactions. Jia et al. [11] were prepared by in situ polymerization PMMA / SWNT composites. The results show that there is a strong bond to write papers effect between carbon nanotubes and the polymer matrix . This is mainly because the carbon nanotubes open AIBN initiator π key process involved in making the polymerization of PMMA . Using a surface-modified carbon nanotubes prepared by PMMA / carbon nanotube composites , not only can improve the ratio of carbon nanotubes dispersed in the polymer matrix , the mechanical properties of the composites can be obtained mechanically huge improvement .
2 Situation Polymer / Carbon Nanotube Composites
聚合物/碳纳米管复合材料的研究现状
2.1 polymer / carbon nanotube composites
Nanotubes because of their extraordinary strength and stiffness and is considered to be the ideal filler for preparing a new generation of high-performance structural composites. In recent years , researchers for the polymer / carbon nanotube composites mechanical properties of the mechanical aspects of the research carried out , which is most impressive with the addition , the elastic modulus of the composite material of carbon nanotubes , tensile strength and fracture toughness increased.
Improve the mechanical properties of the polymer main problem is that they must have good dispersion and distribution in the polymer matrix and increase their interaction with the polymer chain. By optimizing the processing conditions and surface chemical properties of carbon nanotubes , a little added amount has been able to make to achieve significant performance improvement. Expected maximum efficiency in the directional structure ( such as films and fibers ) in , enough to let axis to maximize the performance . Add the amount of fiber in a continuous , single-walled carbon nanotubes has reached more than 60 %, and the measured toughness quite prominent . In addition, more than just add a small amount of fiber wall or single-wall nanotubes , showing the strength of a larger increase . General only a few micron diameter fibers , nano-scale additives can only be used to enhance . Sun Yan Ni et al [ 12 ] carboxylated carbon nanotubes after treatment with high-density polyethylene (HDPE) composite , were prepared by melt blending of carbon nanotube / high density polyethylene composites , and mechanical properties were studied . The results showed that: a carbon nanotube is added to improve the yield strength and tensile modulus of the composite material , but it reduces the breaking strength and breaking elongation of the material . Liu et al [ 13 ] using the melt-mixing method had MWNT/PA6 ( nylon 6 ) composites, the results show that , CNTs have been very evenly dispersed in the PA6 matrix between CNTs and polymer matrix and has a very strong effect of interfacial adhesion when adding 2 wt% ( mass fraction ) of MWNTs, PA6 elastic modulus and yield strength increased by 214% and 162 %. In short , the impact of carbon nanotubes on the mechanical properties of the composites , in large part depends on its mass fraction, and the dispersion of the interaction between the nanotubes and the matrix . Other factors , such as carbon nanotube orientation in the composite , the fiber orientation in the slice layer , as well as the functional groups on the carbon nanotube surface modification inhomogeneity, may also help to improve the mechanical properties of the final composite.
2.2 polymer / carbon nanotube composite function
2.2.1 Conductive Composites
Polymer / carbon nanotube conductive composite material is electrostatic spraying , electrostatic elimination and cleansing the ideal material for the manufacture of disk space and other areas . GE Company [ 14 ] Preparation of conductive carbon nanotube composite material , the carbon nanotube fraction of 10% of the mass of various engineering plastics such as polycarbonate , polyphenylene ether, polyamide and conductive carbon black and rate than the metal fibers time for packing high, this conductive composites both impact toughness , and easy to operate, has been widely used in the car body . LNP company successfully prepared dissipative material that adding carbon nanotubes in PEEK and PEI , and for the production of wafer cassette and disk drive components. It ionic contamination is lower than the carbon fiber 65% to 90% . Japan's Mitsubishi Chemical Corporation also successfully used direct dispersion method to produce a PC containing a small amount of carbon nanotubes composite material , the surface very smooth , excellent physical properties , is ideal for antistatic materials [ 15 ] . In addition, the resistance of polymer / carbon nanotube conductive composites can be achieved with the change of external forces through - off operation , as well as pressure sensors can be used for touch- control switch [ 16 ] ; using resistance of the material nature of the various chemical gases and concentration sensitivity , can be made of gas-sensitive detector, and a gas mixture of various classification or quantitative detection and monitoring [ 17 ] ; using positive temperature effect of the material, i.e., when the crystallization temperature was raised to the polymerization near the melting point , the resistance increases rapidly several orders of magnitude , and when the temperature drops back to room temperature, the resistance value and return to the initial value , the circuit can be used to automatically adjust the output power , temperature -controlled switch [ 18 ] .
2.2.2 The thermal conductivity of composite materials
Many studies demonstrated that carbon nanotubes are the best by far what is known thermal conductivity material . Scientists predict that SWNT thermal conductivity at room temperature of up to 6600 W / mK [19], and the separated multi-walled carbon nanotubes in the thermal conductivity at room temperature is 3000 ~ 6600 W / mK. Thus conceivable , carbon nanotubes can be significantly increased and the thermal conductivity of the composite thermal stability at high temperatures [ 20 ] . Wu et al [ 21 ] were prepared by multi-walled carbon nanotube / high density polyethylene (MWNTs / HDPE) composite materials , and conducted in-depth research on thermal performance , experimental results show that : the thermal conductivity with increasing MWNTs content and up high . When the mass fraction of MWNTs reached 38 h, the thermal conductivity of the composite material is three times higher than that of pure HDPE and more . Xu Ming et al [ 22 ] prepared by in situ polymerization of aligned carbon nanotubes / poly (methyl methacrylate) nanocomposites under an atmosphere of nitrogen and air , thermal decomposition temperature than the composite matrix material were increased by about 100 and 60 ℃. The thermal conductivity, making an array of carbon nanotubes added thermal conductivity of the composites reached 3.0 W / mK, compared with pure PMMA increased by nearly 13 times .
2.2.3 Other features composite materials
In the carbon nanotube / polymer functional composite material aspects of nanotechnology research center recently Engineering , Nanchang University [ 23 ] developed a multi-walled carbon nanotube / epoxy composite material absorbing stealth . Multi- walled carbon nanotubes by high temperature NaOH treatment, the carbon nanotubes produce more holes in its surface , increasing the surface activity of carbon nanotubes ; absorbing stealth composite material has good absorption of radar absorbing effect and controllability band , this absorbing composite volume resistivity at 106 ~ 107 · cm magnitude , with excellent antistatic ability , which adjust the radar absorbing materials for absorbing absorbing bands and broaden the bandwidth of great significance. Clemson University Rajoriat [24] multi -walled carbon nanotubes on the damping properties of epoxy resin were studied and found that carbon nanotube polymer composites than pure epoxy damping ratio increased by about 140%.
3 Preparation of carbon nanotube polymer composites Problems
制备碳纳米管聚合物复合材料中存在的问题
3.1 nanotubes dispersed in the matrix of the problem
Aspect ratio of carbon nanotubes is large, high surface energy , easily agglomerate , it is difficult to uniformly disperse in the polymer. How to achieve uniform dispersion of carbon nanotubes in a polymer matrix is the primary need to solve the current problem . The surface -modified carbon nanotubes can be uniformly dispersed in the polymer matrix , chemical agents can be used , or high -energy discharge , ultraviolet irradiation treatment methods nanotubes, certain functional groups introduced . Liu J et al [25 ] Firstly, the volume ratio of 3:1 concentrated sulfuric acid and concentrated nitric acid oxidation of the Unit -walled carbon nanotubes , to give the end portion of the carboxyl group -containing carbon nanotubes , which are dispersed in various solvents to improve the sex . ChenQD [26] The carbon nanotubes by plasma radiation treatment after the introduction of the polysaccharide chain. Mechanical stress can also be activated using surface modification of carbon nanotubes , by crushing , friction, ultrasound and other means of implementation.
3.2 Orientation of carbon nanotubes
Oriented nanotubes in the polymer material shall conform to the requirements of the force , research shows that by blending certain processing such as mechanical shearing can improve the orientation of the carbon nanotubes in the polymer , thus further improving the performance of composite materials. Jin L [27] The multi-wall carbon nanotubes in a thermoplastic polymer is dissolved in the solution was evaporated and dried to prepare a carbon nanotube thin film was dispersed state of disorder , then heated above its softening temperature and a constant mechanical load pull Shen, allowed to cool to room temperature under load was found by mechanically stretched composite aligned carbon nanotubes can be achieved in the composite .
3.3 composite molding problems
Current carbon nanotube / polymer composites molding generally take molding, solution casting and other means , simple molding operation, easy industrialization, but in the cooling process , the surface of the sample due to the large difference in temperature cracking and other problems will occur ; sample solution casting formed affected by external factors such as stress , but the process of removing the solvent longer nanotubes easy reunion happen.
Additionally , polymer -modified filler used to enhance the original micron glass fiber, organic fiber, carbon nanotubes grown to now , the size change of the filler material of the composite material on the existing processing techniques and characterization methods are facing new challenges, the need in the future to develop the atomic level of new processing techniques and characterization methods to meet the needs of the development of carbon nanotube polymer composites .
Conclusion
结语
Its unique properties of carbon nanotubes are being increasingly applied in many fields , with the progress of science and technology issues during the preparation of the current carbon nanotube composite material existence will gradually be resolved someday nanotechnology will really go to real life when people come to people's lives drastically change.
