Density measurement of size selected multiwalled carbon nanotubes by mobility-mass characterization
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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Present address: Department of Nanosystem and Nanoprocess Engineering, Pusan National University, Korea.