(133g) A Molecular Dynamics Study of Single-Walled Carbon Nanotubes (SWCNTs) Dispersed in Bile Salt Surfactants

A Molecular
Dynamics Study of Single-Walled Carbon Nanotubes (SWCNTs) Dispersed in Bile
Salt Surfactants[*]

Frederick R. Phelan
Jr.[?]^,1  and Huai Sun²

¹Materials Science
and Engineering Division, NIST, Gaithersburg, MD 20899

²Aeon Technology
Inc. and School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University,
Shanghai, China

 
Abstract

Separation
of single-walled carbon nanotubes by chirality is an important aspect of
nanotube metrology. Density gradient ultra-centrifugation (DGU) has emerged as
one of the most important tools for chirality separations, and relies heavily
on the use of bile salt surfactants to create buoyant density differences between
tubes of different chirality, based on the size and packing structure of the
hydration shell surrounding the dispersed tube [1-4]. However, even
though DGU is extensively used, a greater understanding the surfactant
self-assembly mechanism and packing structures for bile salt surfactants and
co-surfactants of different functionality is greatly needed [3-4], as the efficacy 
of the separations depends critically on the details of the SWCNT/surfactant
complex that forms during the dispersion stage. In this work, we study the
behavior of a family of bile salt surfactant and co-surfactant mixtures for a
variety of metallic and semi-conducting SWCNT chiralities. The goal is to
provide a greater understanding of how small changes in surfactant
functionality, e.g., sodium deoxycholate (DOC), sodium taurodeoxycholate (TDOC),
and sodium cholate (SC), promote different packing densities critical to DGU
separations, and compare with recent experimental results [4]. The force field
parameters used in the simulations are developed based on the Consistent
Force-Field (CFF) potential using the Direct Force-Field 7.0 (DFF7) software [5], and will be
stored in WebDFF, an open and extensible, smart force-field repository being
developed at NIST in collaboration with Aeon Technology, as part of the
Materials Genome Initiative (MGI).

References

[1]   M. S. Arnold,
S. I. Stupp, and M. C. Hersam, ?Enrichment of Single-Walled Carbon Nanotubes by
Diameter in Density Gradients,? Nano Lett., vol. 5, no. 4, pp. 713?718,
Apr. 2005.

[2]   M.
S. Arnold, A. A. Green, J. F. Hulvat, S. I. Stupp, and M. C. Hersam, ?Sorting
carbon nanotubes by electronic structure using density differentiation,? Nat
Nano, vol. 1, no. 1, pp. 60?65, Oct. 2006.

[3]   F.
Bonaccorso, T. Hasan, P. H. Tan, C. Sciascia, G. Privitera, G. Di Marco, P. G.
Gucciardi, and A. C. Ferrari, ?Density Gradient Ultracentrifugation of
Nanotubes: Interplay of Bundling and Surfactants Encapsulation,? J. Phys.
Chem. C, vol. 114, no. 41, pp. 17267?17285, Oct. 2010.

[4]   J.
A. Fagan, M. Zheng, V. Rastogi, J. R. Simpson, C. Y. Khripin, C. A. Silvera
Batista, and A. R. Hight Walker, ?Analyzing Surfactant Structures on Length and
Chirality Resolved (6,5) Single-Wall Carbon Nanotubes by Analytical
Ultracentrifugation,? ACS Nano, Mar. 2013.

[5]   ?DFF
7, AeonTechnology.? [Online]. Available:
http://www.aeontechnology.com/Product_DFF.php. [Accessed: 13-May-2013].