Double-Walled Carbon Nanotubes
Double-walled carbon nanotubes in dry powder form ready for dispersion
Allows high doping concentrations without affecting properties of the nanotube
Double-walled carbon nanotubes (DWCNTs) belong to the family of one-dimensional materials, similar to single-walled carbon nanotubes. This particular class of carbon nanotube consists of two nanotubes, with one nested within the other. The differences in the diameters of the two nanotubes can produce varying degrees of interaction between the two tubes. This allows for modifications to be made to the outer nanotube without altering the inner nanotube's properties, and results in unique and interesting properties. Additionally, DWCNTs enable a combination of solubility and functionality (which is not possible with single-walled carbon nanotubes).
At Ossila, we sell DWCNT's along with carboxylic acid (-COOH) and hydroxyl (-OH) functionalised versions.
What are Double-Walled Carbon Nanotubes?
DWCNTs consist of two individual carbon nanotubes, with one embedded inside the other. The differences in diameters and the chirality of the two different nanotubes lead to a varying degree of interaction between the two, while at the same time the properties of the individual nanotubes being separate from each other. It is this wide variety of possibilities that have made DWCNTs a focus of interest for carbon nanotube research. Varying chirality allows a range of inner-wall outer-wall interactions to occur, because the chirality determines whether the nanotube will be semiconducting or metallic. It is possible to achieve metallic-metallic, semiconducting-metallic, metallic-semiconducting or semiconducting-semiconducting interactions. In addition to this, the metallic and semiconducting properties can vary depending upon the exact lattice parameters, which enables a wide range of possible property combinations.
DWCNTs also have a large advantage over single-walled carbon nanotubes, as it is possible to modify the outer nanotube without changing the properties of the inner nanotube. This modification could be either through functionalisation (to add solubilising groups), or the doping of the structure (to alter the properties). This allows the double-walled system to maintain functionality of a single-walled nanotube whilst simultaneously having the solubility of functionalised nanotubes. This combination makes double-walled systems attractive for use as additives in composite materials as it allows high doping concentrations without affecting the properties of the nanotube overall.
The biggest barriers for DWCNTs - with regards to further research and commercialisation - are their synthesis and purification. The yields produced by various synthesis techniques can vary from around 50% to 90% for arc discharge. Similarly, for catalytic chemical vapour deposition the yields can vary from 70% to 85%. The remainder of the nanotubes synthesised using these techniques are a mixture of single-walled and multi-walled nanotubes which then need to be purified to obtain individual double-walled nanotubes. The process of purification is much more difficult. Methods such as high-temperature oxidation result in preferential oxidation of single-walled nanotubes over double-walled. However, the process can damage the remaining nanotubes and will leave residual multi-walled contaminants behind. Other processes, such as ultra-centrifugation, can be used to obtain high-purity DWCNT samples and sort double-walled samples by outer diameter. However this process is labour and time intensive making commercialisation and large scale production of high purity DWCNTs difficult.
Just like with single-walled carbon nanotubes, there are many different areas in which DWCNT's can be applied due to their impressive mechanical and electrical properties. In addition double-walled nanotubes show an increase in the mechanical strength, thermal stability, and also chemical stability over that of single-walled nanotubes. However, the ability to combine different nanotube types have the potential to result in interesting optical, electronic and mechanical properties that are not possible with single-walled nanotubes, and could result in the most interesting research in the coming years.
Similarly to single-walled carbon nanotubes, DWCNTs are insoluble. But by using a combination of surfactants and ultrasonic vibration, it is possible to disperse and suspend small concentrations of nanotubes. For dispersing in aqueous solutions, we recommend the use of sodium dodecylbenzene sulfonate if an ionic surfactant is suitable. If a non-ionic surfactant is needed, we recommend surfactants with high molecular weights.
- Weigh out the desired amount of carbon nanotubes.
- Mix together your solvent and surfactant of choice at the desired surfactant concentration. This should be below the critical micelle concentration of the surfactant.
- Add the solvent-surfactant mix to the dry powder and shake vigorously to mix.
- Either place an ultrasonic probe into the solution or place the solution into an ultrasonic bath. Be careful about the length of time and power used - as damage to the carbon nanotubes can occur, shortening their average length.
- The resulting solution will be a mixture of suspended single walled nanotubes and bundles of single walled nanotubes; further sonication will help break up the bundles.
- To separate out the individual nanotubes in solution from the bundles, the solution should be placed into a centrifuge. If the solution is centrifuged for a longer time and/or at a higher speed, the smaller bundles will be removed narrowing the distribution of suspended nanotubes.
Functionalized DWCNT's can be dispersed without the use of surfactants, a maximum of 0.1mg/ml can be achieved for COOH and OH.
- Double-Walled Carbon Nanotubes: Challenges and Opportunities, C. Shen et. al. Nanoscale, 3, 503-518, (2010) DOI: 10.1039/C0NR00620C
- Properties and Applications of Double-Walled Carbon Nanotubes Sorteb by Outer-Wall Electronic Type. A. A. Green et. al., ACS Nano, 5, 2011, 1459-1467, (2011) DOI: 10.1021/nn103263b
- Linking Chiral Indicies and Transport Properties of Double-Walled Carbon Nanotubes, M. Kociak et. al., Phys. Rev. Lett., 89, 155501, (2002), DOI: 10.1103/PhysRevLett.89.155501
- Double-Walled Carbon Nanotube Solar Cells. J. Wei et. al., Nano Lett., 7, 2317-2321, (2007) DOI: 10.1021/nl070961c
- Raman Spectroscopy Study of Isolated Double-Walled Carbon Nanotubes with Different Metallic and Semiconducting Configurations, F. Villalpando-Paez et. al., Nano Lett., 8, 3879-3886, (2008), DOI: 10.1021/nl802306t
|Recommended Dispersants||DI Water, DMF, THF, Ethanol, Acetone|
|Synonyms||Double-Walled Carbon Nanotubes, Double Wall Carbon Nanotube, Carbon Nanotube, DWNT, DWCNT, CNT|
|Classification / Family||1D materials, Carbon nanomaterials, Nanomaterials, Polycyclic aromatic hydrocarbons, Thin-film electronics|
|Colour / Appearance||Black, fibrous powder|
All our DWCNT come packed as dry powders, which can be dispersed within the user's solvent of choice.
Double-Walled Carbon Nanotube Powders
|Outer Diameter||2 - 4 nm|
|Internal Diameter||1 - 3 nm|
|Specific Surface Area||350 m2.g-1|
|Sale Quantities||250 mg, 500 mg, 1 g|
Functionalised Double-Walled Carbon Nanotube Powders
|Outer Diameter||2 - 4 nm||2 - 4 nm|
|Internal Diameter||1 - 3 nm||1 - 3 nm|
|Length||~50 μm||~50 μm|
|Specific Surface Area||350 m2.g-1||350 m2.g-1|
|Functional Group Wt.%||~2.6%||~3%|
|Sale Quantities||250 mg, 500 mg, 1 g||250 mg, 500 mg, 1 g|
*For larger orders, please contact us to discuss prices.
To the best of our knowledge the information provided here is accurate. However, Ossila assume no liability for the accuracy of this page. The values provided are typical at the time of manufacture and may vary over time and from batch to batch. All products are for laboratory and research and development use only, and may not be used for any other purpose including health care, pharmaceuticals, cosmetics, food or commercial applications.