Elsevier

Carbon

Volume 47, Issue 5, April 2009, Pages 1297-1302
Carbon

Density measurement of size selected multiwalled carbon nanotubes by mobility-mass characterization

https://doi.org/10.1016/j.carbon.2009.01.011Get rights and content

Abstract

We employ a combination of gas phase particle mobility and mass methods to make the first absolute density measurement of gas phase grown carbon nanotubes (CNTs). The approach combines a tandem differential mobility analyzer and aerosol particle mass analyzer in series to achieve two steps of electrical mobility classifications of the CNTs and one of mass classification. In the first mobility classification step a stream of monodisperse catalytic particles was produced by pulsed laser ablation. These mobility-classified catalysts seeded the aerosol growth of CNTs, where were directly passed to a second electrical mobility classification step which allows classification of the diameter-controlled CNTs in length. These diameter- and length-classified CNTs were finally introduced into the aerosol particle mass analyzer to measure their mass distribution. We found that the condensed phase density of CNTs was 1.74 ± 0.16 g/cm3 for two different groups of CNTs with diameters of ∼15 and ∼22 nm. This value is lower (about 3 sigma) than for graphite, and about 1 sigma lower than the average value for density measurements for carbon black.

Introduction

This paper describes what we believe to be the first measurements of the density of multiwalled carbon nanotubes (CNTs). Our density corresponds to the condensed phase density of the CNTs and is based on measurements of the mass and volume of the nanotubes in an aerosol form. These measurements are made on nanotubes that all have essentially the same diameter and length. The ability to generate such nanotubes is an essential feature of the experiment. In this approach, we employ the differential mobility analyzer (DMA) and the aerosol particle mass analyzer (APM) in series to measurement the volume and mass of CNTs on-the-fly. The density of CNTs is obtained by taking the ratio of measured mass to volume.

Section snippets

Experimental

This approach was in part inspired by the study by Park et al. [1], who measured the condensed phase density of fractal-like diesel agglomerates consisting of spherical primary particles. While the structure of a CNT is much different than a soot agglomerate, in both cases there is a similar relationship between the projected area of the particle and its electrical mobility. This relationship is key to the analysis.

The volume of the nanotube is obtained using a DMA, which is widely used in

Conclusions

In this paper we have developed an on-the-fly approach to measure the density of MWCNT’s. More generically we also point out that the tandem DMA–APM technique described in this work enables one to make real-time measurements of the density of nanoscale elongated non-spherical materials with high aspect ratio (e.g. nanowires, nanofibers, or nanotubes), which have masses down to sub-femtograms.

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1

Present address: Department of Nanosystem and Nanoprocess Engineering, Pusan National University, Korea.

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