Carbon nanotubes aspect ratio

MWNT PVA 89,000-98,000, (99+% hydrolyzed) Water/ ethanol (3 1) 4 Effect of carbon nanotube aspect ratio and loading on elastic modulus [90]... 

Chen L., Ozisik R., and Schadler L. S., The influence of carbon nanotube aspect ratio on the foam morphology of MWNT/PMMA nanocomposite foams. Polymer 2010, 51, 2368-2375. 

Fillers with extremely high aspect ratios (1000-10,000) such as carbon nanotubes (Figure 32.5) have a much lower percolation threshold (lower amount is required for equivalent reinforcement). 

CNTs may consist of just one layer (i.e. single-walled carbon nanotubes, SWCNTs), two layers (DWCNTs) or many layers (MWCNTs) and per definition exhibit diameters in the range of 0.7 < d < 2 nm, 1 < d < 3 nm, and 1. 4 < d < 150 nm, respectively. The length of CNTs depends on the synthesis technique used (Section 1.1.4) and can vary from a few microns to a current world record of a few cm [16]. This amounts to aspect ratios (i.e. length/diameter) of up to 107, which are considerably larger than those of high-performance polyethylene (PE, Dyneema). The aspect ratio is a crucial parameter, since it affects, for example, the electrical and mechanical properties of CNT-containing nanocomposites. 

Thus, carbon nanotubes are naturally of interest due to their very large aspect ratio, h/r. 

Carbon nanotubes are hollow carbon cylinders with hemispherical endcaps of less than 1 nm to a few nanometres in diameter and several microns in length. The aspect ratios are of the order of 1000 and more. The elementary nanotubes agglomerate in bundles or ropes that are difficult to disperse. 

While carbon fiber (thickness on the order of 1000 nm) composites offer very strong materials, carbon nanotubes make even stronger composites. These carbon nanotubes have aspect ratios of over 1000 (ratio of length to diameter). Further, because some carbon nanotubes are electrically conductive, composites containing them can be made to be conductive. A number of carbon nanotube matrixes have been made including using a number of engineering resins, such as polyesters, nylons, polycarbonates, and PPE. 

Carbon nanotubes as pseudo-one-dimensional carbon allotropes of high aspect ratio, high surface area, and excellent material properties such as ultimate electrical and thermal conductivities and mechanical strength have generated much excitement in the nanoscience and nanotechnology community.1-3 These all-carbon hollow... 

Table 5.1. Carbon nanotubes have a high potential to improve the mechanical, physical and electrical properties of polymers, as stated by Thostenson et al. (4). They exhibit an exceptionally high aspect ratio in combination with low density, as well as high strength and stiffness (Coleman et al. (5)), which make them a potential candidate for the reinforcement of polymeric materials.

The gap between the predictions and experimental results arises from imperfect dispersion of carbon nanotubes and poor load transfer from the matrix to the nanotubes. Even modest nanotube agglomeration impacts the diameter and length distributions of the nanofillers and overall is likely to decrease the aspect ratio. In addition, nanotube agglomeration reduces the modulus of the nanofillers relative to that of isolated nanotubes because there are only weak dispersive forces between the nanotubes. Schadler et al. (71) and Ajayan et al. (72) concluded from Raman spectra that slippage occurs between the shells of MWNTs and within SWNT ropes and may limit stress transfer in nanotube/polymer composites. Thus, good dispersion of CNTs and strong interfacial interactions between CNTs and PU chains contribute to the dramatic improvement of the mechanical properties of the... 

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