Composite Materials with Carbon Nanotubes

The mechanical properties of isolated SWNT in particular (Section 3.4.3) turn them into nothing short of a fiUer par excellence for polymer composites. However, the embedding of individual, completely debundled carbon nanotubes in the polymer matrix still poses large problems. This is why, for the time being, the materials produced do by far not reach the envisaged improvement of characteristics Bundles of nanotubes feature much worse mechanical properties as there 

Composites of multiwalled tubes are distinct from those with SWNT filler in other respects too. MWNT composites normally exhibit a different resistance regarding compression and expansion. This may be explained by the compression acting on aU individual walls of the MWNT, whereas only the outer shell is exposed to tensile forces. Especially in the latter case the interwaU sUding mentioned above becomes relevant. 

In general there are two ways of embedding the nanotubes. Firstly, such composites with the interaction between polymer and nanotube exclusively basing on noncovalent forces may be prepared. These can be obtained by simple admixture. 

Secondly, however, the carbon nanotube may be covalently functionalized with monomer units, initiator molecules or crosslinking groups, which leads to a significantly better interaction with the matrix. 

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Polystyrene For polystyrene, both covalently and noncovalently bound composite materials with carbon nanotubes are known. Polystyrene, like the methacrylates, can be generated by surface-initiated radical polymerization on nanotubes functionalized with initiator molecules (in analogy to Figure 3.86). Suitable substances then actually include analogous compounds like in the case of polymethacrylates. 

Levitsky lA, Kanelos P, Euler WB (2004) Electromechanical actuation of composite material from carbon nanotubes and ionomeric polymer. J Chem Phys 121 1058-1165 Lin J, Liu Y, Zhang QM (2011) Charge dynamics and bending actuation in Aquivion membrane swelled with ionic liquids. Polymer 52 540-546... 

Sahoo, N. G., Jung, Y. C., Cho, J. W. (2007a), Electroactive shape memory effect of polyurethane composites fiUed with carbon nanotubes and conducting polymer. Materials and Manufacturing Processes, 22,419-23. 

W.-T. Hong and N.-H. Tai, "Investigations on the thermal conductivity of composites reinforced with carbon nanotubes," Diamond Related Materials, vol. 17, pp. 1577-1581, 2008. 

There is currently considerable interest in processing polymeric composite materials filled with nanosized rigid particles. This class of material called "nanocomposites" describes two-phase materials where one of the phases has at least one dimension lower than 100 nm [13]. Because the building blocks of nanocomposites are of nanoscale, they have an enormous interface area. Due to this there are a lot of interfaces between two intermixed phases compared to usual microcomposites. In addition to this, the mean distance between the particles is also smaller due to their small size which favors filler-filler interactions [14]. Nanomaterials not only include metallic, bimetallic and metal oxide but also polymeric nanoparticles as well as advanced materials like carbon nanotubes and dendrimers. However considering environmetal hazards, research has been focused on various means which form the basis of green nanotechnology. 

Nonconjugated hydrocarbon polymers could also be combined with carbon nanotubes, with polystyrene being the most studied example. The composites are generally prepared by solution or shear mixing techniques, resulting in materials with improved mechanical properties [60]. 

Encapsulation of other material into carbon nanotubes would also open up a possibility for the applications to electrodevices. By applying the template method, perfect encapsulation of other material into carbon nanotubes became possible. No foreign material was observed on the outer surface of carbon nanotubes. The metal-filled uniform carbon nanotubes thus prepared can be regarded as a novel onedimensional composite, which could have a variety of potential applications (e.g novel catalyst for Pt metal-filled nanotubes, and magnetic nanodevice for Fe304-filled nanotubes). Furthermore, the template method enables selective chemical modification of the inner surface of carbon nanotubes. With this technique, carbon... 

The unique two-phase structures of polyurethane that offers the elasticity of rubber combined with the toughness and durability of metal make them one of the most extensively studied and frequently used materials in carbon nanotube related nanocomposites. The main difficulty in developing CNT based polyurethane nanocomposites was how to achieve uniform and homogeneous CNT dispersion. Further investigations on the interactions between carbon nanotubes and two-phase structures are critical for the wider applications of carbon nanotube/polyurethane composites. 

Composites with Other Polymers Besides the composite materials presented so far, a multitude of further polymer composites with carbon nanotubes has been prepared and studied regarding their properties. After all, any given polymer is suitable to some extent to interact with different carbon nanotubes (pristine or functionalized). The number and range of possible combinations surpass the scope of this text, so the examples mentioned below inevitably have to remain incomplete. 

Figure 5.1 The three types of CNT structures (a) armchair, (b) zigzag, (c) chiral. (Reprinted with permission from International Materials Review, Carbon Nanotube Composites by P. J. F. Harris, 49, 1, 31 3. Copyright (2004) Maney Publishing www.maney.co.uk/journals/lmr)...

Carbon nanotubes are multifunctional materials used as large surface area providing conductive fillers, and are responsible for the enhancement of electrical, thermal, and mechanical properties of any polymeric nanocomposite. Polyaniline composited with carbon nanotubes show enhanced electronic properties due to the charge transfer processes between polyaniline and carbon nanotubes. Polyaniline/carbon... 

Loos (2011) reported that investigators from Bayer Material Science LLC, USA and Moulded Fibre Glass, Cleveland, USA have developed a prototype wind turbine blade 0.74 m long manufactured from polyurethane reinforced with carbon nanotubes (CNT PU). The researchers claim that the advanced material has a specific tensile strength five times and 60 times that of carbon fibre composite and aluminium, respectively, and is tougher than carbon fibre-reinforced polymer (CFRP) but the excellent properties of these materials come with a price penalty. 

Abot JL, Song Y, Vatsavaya MS, Medikonda S, Kier Z, Jayasinghe C, et al. Delamination detection with carbon nanotube thread in self-sensing composite materials. Compos Sci Technol 2010 70(7) 1113-9. 

Innovations in Materials. Carbon nanotubes have been heralded as a future super-material with strength hundreds of times that of steel for the same mass. As of the first decade of the twenty-first century, the longest strands of carbon nanotubes developed are still on the order of a few centimeters. This is a very impressive length-to-diameter ratio. Composite materials incorporating carbon already find wide use in various applications where high temperatures must be encountered. Metal matrix composites find use in primary structures even for commercial aircraft. Several smart structures have been developed, where sensors and actuators are incorporated into a material that has special properties to respond to stress and strain. These enable structures that will twist in a desired direction when bent or become stiffer or more flexible as desired, depending on... 

Nano-additives are able to functionalize the materials to a greater extent or can even be used to produce hybrid composites [5,6]. Even the fibers can be composites themselves, for example, where microfibers or even nanofibers are reinforced with carbon nanotubes (CNTs) [7,8] or with nanoclay [9,10], etc. In these cases nano-reinforcement is typically embedded into a fiber which becomes a kind of matrix itself. These composite fibers can have excellent tensile properties [7] or can be used for detecting damage in composite structures [11] or can be precursors of carbon fibers [12]. 

Abot, J., et al. Novel carbon nanotube array-reinforced laminated composite materials with higher interlaminar elastic properties.Compos.5ci.7ec/z o/.2008, 65(13), 2755-2760. 

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