Nanotube Composites with Different Polymers

In the following sections some examples of covalently and noncovalently bound carbon nanotube composites are presented. They are ordered by classes of substances as in most cases composites with both modes of bonding are known. 

The procedure normally employed in the production of PMMA-nanotube composites is the surface initiated polymerization (SIP). The initiator molecule may be tethered to the nanotube via various linkers. Bromoisobutyric acid is frequently 

The resulting PMMA composite materials are insoluble in both organic or aqueous media. Hence alternative acrylates soluble even in their polymerized state have been sought for. Especially poly-tert-butyl acrylates suit weU to this purpose. Furthermore, the tert-butyl residues are easy to remove from these composites, so water soluble polyacrylic acids with additional carbon nanotubes are obtained. 

Another species of polyanilines, the poly-(m-aminobenzenesulfonic acid) (PABS) forms nanotube composites as weU. Up to SmgmT of these dissolve in water due to the existing sulfonic acid groups. The first internal doping in a nanotube composite ever has been observed for these materials. It has been detected by the signal position in the IR-spectrum that is indicative of an electronic hybrid structure with states situated between those of the composites in their ground state. 

The composite preparation is achieved by dispersing the SWNT in a solution of the polymer (e.g., in chloroform) and subsequently removing the solvent in vacuo. 

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Cao et al. (44) reported nanotube incorporation in Chitosan with medium molecular weight. The polymer, MWNTs and the composites with different fractions of MWNTs were characterized by X-ray diffraction. The MWNTs exhibited a sharp diffraction peak at about 20... 

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. 

Nanotube nanocomposites with a large number of polymer matrices have been reported in the recent years. The composites were synthesized in order to enhance mechanical, thermal and electrical properties of the conventional polymers so as to expand their spectrum of applications. Different synthesis route have also been developed in order to achieve nanocomposites. The generated morphology in the composites and the resulting composite properties were reported to be affected by the nature of the polymer, nature of the nanotube modification, synthesis process, amount of the inorganic filler etc. The following paragraphs review the nanocomposites structures and properties reported in a few of these reports and also stress upon the future potential of nanotube nanocomposites. 

As-synthesized MWCNT and SWCNT exist as bundles or ropes and tend to agglomerate due to strong van der Waals forces (13) (Figure 7.1). Unless the CNTs are separated in to individual tubes and dispersed in the polymer matrix, the interactions of the nanotubes with the polymer will be weak. The mechanical failure of such composites will occur due to slippage of the tubes in the bundle that are not bonded to the matrix. In addition, the aggregates or bundles reduce the aspect ratio of the reinforcement which affects electrical properties as well (15). Because of these factors the first step will be to open up these bundles to separate individual tubes by using different techniques to increase the volume of interface between the CNT and the matrix (40). 

In the section devoted to CNTs, some details concerning synthesis and purification methods, as well as separation techniques for metalfic and semiconducting nanotubes will be reviewed. Some aspects concerning the interactions of CNTs with reactants used in the synthesis of different composites based on conducting polymers, such as PANI, PPy, PEDOT, PBTh, PNVK, PPV, and polyfluorene (PF) will be discussed in the section devoted to the synthesis of the CP/CNT composites. Preparing a composite with the desired properties requires knowledge of the interaction between the host matrix and the guest carbon nanoparticles. 

One-dimensional nanostructured polymer composite materials include nanowires, nanorods, nanotubes, nanobelts, and nanoribbons. Compared to the other three dimensions, the first characteristic of one-dimensional nanostructure is its smaller dimension structure and high aspect ratio, which could efficiently transport electrical carriers along one controllable direction, thus is highly suitable for moving charges in integrated nanoscale systems (Tran et al., 2009). The second characteristic of one-dimensional nanostructure is its device function, which can be exploited as device elements in many kinds of nanodevices. With a rational synthetic design, nanostructures with different diameters/... 

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