Carbon nanotubes morphology/dispersion

Dieckmann et al. in 2003 described an amphiphilic a-helical peptide specifically designed to coat and solubilize CNTs and to control the assembly of the peptide-coated nanotubes into macromolecular structures through peptide-peptide interactions between adjacent peptide-wrapped nanotubes [227]. They claimed that the peptide folds into an amphiphilic a-helix in the presence of carbon nanotubes and disperses them in aqueous solution by noncovalent interactions with the nanotube surface. EM and polarized Raman studies revealed that the peptide-coated nanotubes assemble into fibers with the nanotubes aligned along the fiber axis. The size and morphology of the fibers could be controlled by manipulating the solution conditions that affect peptide-peptide interactions [227]. 

Carbon nanotubes displayed a higher specific surface area, which could explain the influence of the carbon nanotube morphology, with mainly an effect of the diameter. Long carbon nanotubes were extremely difficult to disperse in EVA, actually forming well-known associated bundles. 

We review the research on preparation, morphology, especially physical properties and applications of polyurethane (PU)/carbon nanotube (CNT) nanocomposites. First, we provide a brief introduction about the preparation of PU/CNT nanocomposites. Then, the functionalization and the dispersion morphology of CNTs as well as the structures of the nanocomposites are also introduced. After that, we discuss in detail the effects of carbon nanotubes on the physical properties (including mechanical, thermal, electrical, rheological and other properties) of PU/CNT nanocomposites. The potential applications of these nanocomposites are also addressed. Finally, the challenges and the research that needs to be done in the future for achieving high-performance polyurethane/carbon nanotube nanocomposites are prospected. 

PANI/multi-walled carbon nanotube (PANI/MWNT) composites have also been synthesized via an oxidative dispersion polymerization technique for ER fluid application [83], The morphology of PANI/MWNT composite particles seems to be pierced with MWNT like a pearl necklace structure as shown in Figure 14,6a, Under DC electric fields, the PANI/MWNT ER fluid shows a rapid and reversible change in shear viscosity with an applied electric field as shown in Figure 14,6b,... 

A morphological analysis revealed that the blends and composites which contain ethylene ethyl acrylate-maleic anhydride polymer exhibit a better elastomer phase dispersion with smaller domain sizes in comparison to the other elastomer. The addition of the carbon nanotubes also improves the mechanical properties of the samples for both elastomer types [83]. 

When electrical and electronic properties are also of interest apart from mechanical and thermal properties, carbon nanotubes can be of better advantages. Nanotubes are inert in nature and, therefore, also require surface modification in order to achieve compatibility with the polymer matrices. Thus, the nanoscale dispersion of the nanotubes is as important and challenging as the layered silicates as the properties are dependant on the generated morphology in the composites. In a representative study, Teng et al. 

A two-step method was used to prepare carbon nanotube (CNT)/(EVA)/(PE) and CNT/(PC)/PE composites. First, CNT-EVA and CNT-PC master batches were obtained by solution-phase processing, and second, the CNT master batches were melt mixed with PE. Phase morphological observations revealed decrease in the size of the dispersed particles in the composites (Li et al. 2007). 

Similarly, Saeed and Park [65] synthesized PA 6-multiwaIl carbon nanotubes (MWNTs) nanocomposites via the in-situ polymerization technique, using pristine and COOH-functionalized MWNTs. Based on SEM morphology analysis, it was shown that the COOH-functionalized MWNTs were better dispersed in the PA 6 matrix than the pristine ones, owing to the covalent attachment of PA 6 molecular chains to the side walls of MWNTs, which could act as in-situ compatibilizers in the nanocomposites and enhance the dispersion of MWNTs. In terms of physical properties, the crystallization of nanocomposites was increased compared to that of virgin PA 6, due to the nucleation effect of MWNTs, while the thermal stability under nitrogen of the nanocomposites was superior. Turning to the mechanical properties of the nanocomposites, the uniformly dispersed MWNTs improved the tensile properties because of the reinforcement effect. 

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