Multiwall Carbon Nanotubes (MWCNT): Production, Analysis and Application

Table of Contents

Introduction
Properties of MWNTs
Challenges in Commercialization of MWNTs
Characterization of MWNTs and Quality Assurance Parameters
Applications of MWNTs
Conclusion
About Southwest Nanotechnologies

Introduction

Single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs) are similar in certain respects but they also have striking differences. SWNTs are an allotrope of sp2 hybridized carbon similar to fullerenes. The structure is a cylindrical tube including six-membered carbon rings similar to graphite. Analogously MWNTs include several tubes in concentric cylinders as shown in Figure 1.

The number of these concentric walls may vary from 6 to 25 or more. The diameter of MWNTs may be 30 nm when compared to 0.7–2.0 nm for typical SWNTs. The unique properties of carbon nanotubes enable a wide range of novel applications and improvements in the performance of existing ones.

This article offers a brief overview of the physico-chemical nature and characterization of multiwall nanotubes (MWNTs), with specific emphasis on recently introduced materials that signify the most recent advancement of the technology, and the level of its commercialization.

Figure 1. Multi-walled carbon nanotubes

Properties of MWNTs

MWNTs have excellent properties and are being employed in a large number of commercial applications. The properties of MWNTs are:

Challenges in Commercialization of MWNTs

The challenges in commercializing MWNTs include the following:

Characterization of MWNTs and Quality Assurance Parameters

Observational techniques such as SEM, TEM and AFM are used for characterizing MWNTs and can be used to obtain data such as length, diameter and number of walls. Furthermore thermogravimetric analysis (TGA) is used to measure the residual mass, the temperature at the onset of oxidation and the temperature of the maximum oxidation rate.

The shape of the derivative curve provides qualitative information with respect to the uniformity of the sample with reference to polydispersity of the material. A high, narrow peak indicates a narrow distribution of diameters and minimal tube defects.

Applications of MWNTs

There are a large number of present and evolving applications for MWNTs. These include:

Certain features of the SMW product are:

Figure 2. Commodity MWNT and SWeNT® SMW 200 (Aldrich Product No. 773840) TEM and AFM images

Figure 3 shows a comparison of conductivity data for SWeNT® SMW 200 (Aldrich Product No. 773840) when compared to other commercially available MWNTs materials. Determining the sheet resistance of CNT buckypapers (a thin solid film created by filtration of 0.15 g of CNT/m2) shows that as expected a SWNT material (in this case SWeNT® SG76, Aldrich Product No. 704121) has a very low resistivity value. Actually, the SMW 200 purified material is more than twice as conductive when compared to the best MWNT material studied (Competitor A).

Figure 3. Buckypaper resistivity measurements of various CNT products

Figure 4 compares sheet resistance buckypaper data for a range of products as a function of the CNT aspect ratio (L/D), as determined by AFM and TEM analysis. It is observed clearly that trend of lower sheet resistance with higher aspect ratios, with SWeNT® SMW 200 (Aldrich Product No. 773840) having excellent conductivity properties. Further to the CNT aspect ratio it was also observed that the tube morphology is another major factor that strongly impacts tube conductivity.

Figure 4. Sheet resistance of buckypapers as a function of the CNT aspect ratio

Conclusion

MWNTs have been adopted in quite a number of applications, but advancements in their properties are needed for harnessing their potential. Improved MWNTs have been developed that will considerably expand the market reach of this unique category of advanced materials. CoMoCAT® high purity MWNTs manufactured by SWeNT®, Inc. and available in research quantities exclusively from Aldrich® Materials Science are provided in the table below:

Aldrich Prod. No. SWeNT® Product Product Name Features
773840 SMW 200 Carbon nanotube, multi-walled
>98% carbon
6-8 tube walls
  • High purity multi-walled carbon nanotubes
  • High conductivity
  • Excellent dispersibility
  • Lower cost (compared to SWNTs)
724769 SMW 100 Carbon nanotube, multi-walled
98% carbon
6-9 nm diameter
  • High purity multi-walled carbon nanotubes
  • Few-walled
  • Small diameter
  • Lower cost (compared to SWNTs)

About Southwest Nanotechnologies

SouthWest NanoTechnologies Inc. (SWeNT) produces carbon nanotubes using the patented CoMoCAT® catalytic method in fluidized bed reactors. This results in selective synthesis of single-wall carbon nanotubes and remarkable control of diameter, chirality and purity.

Single-wall carbon nanotubes exhibit unique properties due to their unusual structure. They consist of a hollow cylinder of carbon ~ 1nm in diameter, up to 1,000 times as long as it is wide. This structure has remarkable optical and electronic properties, tremendous strength and flexibility, and high thermal and chemical stability. As a result, carbon nanotubes are expected to have dramatic impact on several industries, including displays, electronics, health care and composites.

SWeNT was founded in April 2001 to commercialize nanotube technology developed by Professor Daniel Resasco at the University of Oklahoma. The CoMoCAT® brand is widely recognized for quality and scalability.

This information has been sourced, reviewed and adapted from materials provided by SouthWest NanoTechnologies (SWeNT).

For more information on this source, please visit SouthWest NanoTechnologies (SWeNT).