Nanotubes aspect ratio

This model shows that the requirements for a good reinforcement are a high volume fraction of very well oriented fibers and with high aspect ratios. Nanotube aspect ratios are varying, but are very large, from at least 50 for the shorter and thicker nanotubes to sometimes more than 1000 for the longer and thinner ones. 

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. 

The question whieh then arises is What do we call a defect in a nanotube To answer this question, we need to define what would be a perfeet nanotube. Nanotubes are mieroerystals whose properties are mainly defined by the hexagonal network that forms the eentral cylindrical part of the tube. After all, with an aspect ratio (length over diameter) of 100 to 1000, the tip structure will be a small perturbation except near the ends. This is clear from Raman studies[4] and is also the basis for calculations on nanotube proper-ties[5-7]. So, a perfect nanotube would be a cylindrical graphene sheet composed only of hexagons having a minimum of defects at the tips to form a closed seamless structure. 

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. 

This review focuses on nanoparticles, namely objects that are roughly spherical. We use the commonly accepted definition for nanoscale objects of having a dimension below 100 nm, and so identify nanoparticles as objects with a diameter of 100 nm or smaller. The review does not focus on larger aspect ratio nanoscale materials such as nanotubes and nanorods, though they are mentioned in some cases. 

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. 

Shankar K, Mor GK, Fitzgerald A, Grimes CA (2007) Cation effect on the electrochemical formation of very high aspect ratio Ti02 nanotube arrays in formamide-water mixtures. J Phys Chem C 111 21-26... 

Macak JM, Tsuchiya H, Schmuki P (2005) High-aspect-ratio Xi02 nanotubes. Angew. Chem. Int. Ed. 44 2100-2102... 

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