Extraction of single-wall carbon nanotubes into an organic solvent


Justin J. Hill, jhill@che.ufl.edu1, Randy K. Wang, wrandy@ufl.edu1, Robert H. Hauge2, Richard E. Smalley3, and Kirk J. Ziegler, kziegler@che.ufl.edu1. (1) Department of Chemical Engineering, University of Florida, P.O. Box 116005, Gainesville, FL 32611, (2) Center for Nanoscale Science and Technology, Rice University, Houston, TX 77005, (3) Department of Chemistry, Smalley Institute for Nanoscale Science and Technology, Rice University, 6100 Main Street, MS 100, Houston, TX 77005
Single-walled carbon nanotubes (SWNTs) are currently being studied for a variety of applications. Due to their mechanical strength, chemical stability, and electronic properties, SWNTs lend themselves to technology involving energy storage and transport, and field emission devices. In many applications, however, the length of the SWNTs is particularly important. For example, researchers have recently demonstrated that short-length nanotube transistors performed as well as state-of-the-art silicon-based transistors without any optimization. In addition, the length of the SWNTs has a profound effect on their dispersibility in various solvents, a necessary step in most application processes. While researchers have demonstrated a multitude of cutting processes capable of changing the length distributions of SWNTs, polydisperse length distributions still remain. Currently, most separation processes rely on chromatographic or electrophoretic techniques. While these techniques have demonstrated some degree of separation, the nature of these approaches often limits them to analytical-scale separations. Therefore, economically feasible and scalable methods of cutting and separating SWNTs by length are required. Here we describe a two-phase liquid-liquid extraction process which is capable of extracting water-soluble SWNTs into an organic phase. The extraction utilizes electrostatic interactions between a common phase transfer agent and the sidewall functional groups on the nanotubes. The colloidal interactions between SWNTs, such as van der Waals attraction and steric repulsion, are important aspects that affect the dispersion of SWNTs in the organic layer. Therefore, the large length-dependent van der Waals forces for nanotubes allow the ability to control the length of nanotubes extracted into the organic phase. Although several researchers have investigated the interactions of spherical colloidal particles, there are few studies that describe the van der Waals and steric interactions for 1-D nanotubes. The ability to describe these interactions will lead to improved dispersion of SWNTs and thus, yield more efficient separations and more uniform nanocomposites.