Nanotube Metrology N

Our goal is to develop methods to produce well-characterized 

fractions of carbon nanotube suspensions with controlled parameters 

(length, type, charge, concentration and impurities) and to utilize 

ANOMATERIALS

them for measuring intrinsic nanotube properties and addressing 

emerging EHS concerns. By providing measurements that underlie 

this new class of materials, we allow vendors and buyers to trade 

with confidence and provide the final users with sound knowledge 

of the properties of the material. 

Objective

Impact and Customers

• The global market for nanotubes has the potential to reach $5B by 2012 in electrical, 

mechanical, health and medical applications. We are developing the measurements 

infrastructure that underlies this new material.

• Three biannual workshops on single-walled carbon nanotubes (SWCNTs), jointly 

sponsored by NIST and NASA, have led the way for dissemination of the NIST effort 

to both the industrial and academic communities. The output was a Recommended 

Practice Guide which launched the extensive ISO activities in SWCNTs. Seven 

documentary standards are in preparation by five countries.

• 2009 will see the release of three SWCNT Reference Materials (RMs), each designed 

to address measurement needs reported by the SWCNT community. A SWCNT soot 

RM, a purified SWCNT “bucky paper,” and a set of length separated SWCNTs in 

aqueous dispersion will be released.

• We collaborate with industrial, academic and government researchers including 

Rice University, NASA and SouthWest Nanotechnologies Inc. by providing them with 

analysis of samples of unprecedented quality, by sorting samples into their component 

parts and by providing optical data.

Approach

Materials Science and Engineering Laboratory

In every SWCNT production technique many different types (called chiralities) 

and lengths of SWCNTs are produced. The properties of the SWCNTs are linked 

strongly to both of these parameters. Thus, in order to characterize the intrinsic 

properties of any specific SWCNT type or length, an initially polydisperse nanotube 

sample must be first purified of non-SWCNT carbon and metallic catalyst, and 

then separated by diameter or length to achieve robust results. Characterization 

by optical methods (absorption, fluorescence, Raman scattering), conductivity 

measurements, microscopy or other techniques then yields specific results.

Individual dispersion of the SWCNTs with DNA, or small molecule surfactants such as sodium deoxycholate, enables 

this purification and separation via nondestructive solution phase separation techniques. We use a variety of different 

techniques to separate SWCNTs by chirality or length, depending on the requirements of the characterization we wish 

to perform. Using techniques such as size exclusion chromatography, field-flow fractionation and ultracentrifugation (for 

either length or type separation), highly resolved SWCNT fractions are generated to allow for measurement development 

and individual property determination.

854-05-01b
Materials Science and Engineering Laboratory

Our systematic focus on controlling the 

nanotube population in a sample through 

the utilization and development of separation 

techniques differentiates the NIST effort in 

SWCNTs. Using well controlled populations 

ensures that we can accurately develop 

measurement techniques and characterize 

intrinsic SWCNT properties, resulting in 

greater confidence in measurements by 

nanotube manufacturers, device makers and 

academic researchers.

Controlling the SWCNT population in a 

sample begins with the dispersion process. 

In the dispersion process the SWCNTs 

are brought into an aqueous or organic 

solvent through the use of small molecules 

called surfactants. Our first research was 

to determine the most efficient methods for 

dispersion and dispersion metrology.

Utilizing small angle neutron scattering 

(SANS) to directly measure dispersion, we 

compared measurements from additional 

techniques such as multiple angle light 

scattering, dynamic light scattering, UVvisible-near infrared (UV-Vis-NIR) absorption 

and NIR fluorescence on the best dispersed 

surfactant – SWCNT systems, to develop 

the metrology of dispersion. This work 

identified the best dispersants as small single 

stranded DNA molecules, such as (GT)15, 

and the small molecule surfactant sodium 

deoxycholate.

Length Separation 

We utilize three different techniques to 

perform length separation: size exclusion 

chromatography (SEC), field-flow 

fractionation (FFF), and centrifugation. Each 

technique offers a different, complementary 

balance between size resolution, mass 

throughput, and metrology development. 

Centrifugation based length sorting, 

invented at NIST, allows for the largest scale 

separation. FFF and SEC process smaller 

amounts of material, but allow for higher 

resolution of the separated fractions and 

for online measurement of the separation 

process. For all three techniques we have 

made significant advances to the separation 

science and metrology of SWCNTs. 

We have also subjected the separated SWCNT 

length fractions, ranging from 1μm to less 

than 50 nm, to intense characterization. 

In 2007 this resulted in the publication of 

the previously unrecognized dependence 

of SWCNT optical properties on length. In 

2008 we optimized the parameters for length 

separation via ultracentrifugation, began 

sorting populations by multiple vectors, i.e. 

length and electronic functionality, and used 

our separated materials to explore the effects 

of length on 2D percolation, templated self 

assembly, and the measurement of defect 

density on a nanotube.

The effort involving the 2D percolation of 

nanotubes was particularly interesting, as it 

provided an experimental comparison with 

2D percolation theory. It also showed that 

sorted nanotubes, even of a shorter average 

length, may perform better than unsorted 

tubes due to their tendency to pack in a 2D 

(rather than a 3D) network.

Reference Materials 

Results from these scientific investigations 

have enabled the production in 2009 of 

three grades of Reference Materials (RMs). 

The lowest grade will be a raw SWCNT soot 

characterized for elemental composition. 

More purified materials will include a RM 

composed of a mat of purified SWCNTs 

from the raw soot, and a set of length 

separated fractions in aqueous dispersion, 

also purified from the raw soot base 

material. The absorbance spectra shown for 

the long, medium, and short fractions are 

representative of these solutions.

SWCNT Uptake and Toxicity

The development of SWCNT samples with 

different lengths, and the metrology of 

those samples, are enabling significant new 

investigations and collaborations. In concert 

with the biomaterials group, these samples 

were used for the first determination of the 

effect of length on the uptake of SWCNT 

by multiple cell lines, including human lung 

fibroblasts. In this study we found that only 

the shortest SWCNTs, those less than 200 nm, 

were absorbed at a significant rate by the cells. 

Thus the potential toxicity of these materials 

can likely be significantly reduced by the use 

of SWCNTs longer than this threshold.

Accomplishments

Erik K. Hobbie

Ji Yeon Huh

Kalman Migler

Jan Obrzut

Fred Phelan

Daneesh Simien

Angela Hight Walker

Jeffrey A. Fagan

(Polymers Division)

(301) 975-6740

Jeffrey.fagan@nist.gov

www.nist.gov/polymers

Learn More Publications

Fagan JA, Becker ML, Chun J, Nie P, Bauer BJ, Simpson J, Walker ARH and Hobbie EK 

Centrifugal Length Separation of Carbon Nanotubes Langmuir, 24: 13880 (2008)

Simien D, Fagan JA, Luo W, Douglas JF, Migler K and Obrzut J Influence of Nanotube 

Length on the Optical and Conductivity Properties of Thin Single-Wall Carbon Nanotube 

Networks ACS Nano, 2:1879 (2008)

Becker ML, Fagan JA, Gallant ND, Bauer BJ, Bajpai V, Hobbie EK, Lacerda S, Migler KB 

and Jakupciak JP Length-Dependent Uptake of DNA-Wrapped Single-Walled Carbon 

Nanotubes Advanced Materials, 19: 939 (2007)

Fagan JA, Simpson JR, Bauer BJ, Lacerda S, Becker ML, Chun J, Migler KB, Walker ARH 

and Hobbie EK Length-Dependent Optical Effects in Single-Wall Carbon Nanotubes J. 

American Chemical Society, 129: 10607 (2007)

The effect of length on absorbance A human cell containing SWCNTs The effect of length on percolation