(474g) Hydrodynamic Behavior of Length Sorted Carbon Nanotubes

Anisotropic nanoparticles such as single-walled carbon nanotubes (SWCNTs) can have exceptional physical properties, and there is much interest in developing them through processing techniques while in aqueous dispersion.  However, current understanding of the particle behavior in solution is not sufficient to enable rigorous measurement of critical aspects of a dispersion such as the particle size distribution.  Our goal is to validate the use of hydrodynamic characterization for rod-like nanoparticles such as SWCNTs that have very large ranges of aspect ratios, but constant diameters.

Theoretical approximations that describe the hydrodynamic effects of shape have been developed since the 1930s for 1-D non-spherical particles such as ellipsoids or cylinders.  Experimental verification of such approximations, however, has lagged the theoretical description due to a lack of appropriate particle systems both small enough to satisfy assumptions for the flow fields and with sufficient variability in aspect ratio.  In general, experimental works that have evaluated the friction coefficient of rodlike particles have been limited to low aspect ratios due to these constraints, whether for variable particles such as gold nanorods or DNA, or monomodal rod-like particles such as TMV or Fd virus.

In this work, SWCNTs were used as model rod-like particles to experimentally validate expressions for the friction coefficients that are the result of the slender body theory or numerical methods.  SWCNTs are an ideal model particle for this purpose.  Different length populations of constant buoyancy SWCNTs were generated via centrifugation sorting followed by size exclusion chromatography.  A total of 19 populations of SWCNTs with average aspect ratios varying from approximately 30 to 400 were generated from two different diameter SWCNT samples.  Characterization of the SWCNT sedimentation in an analytical ultracentrifuge was used to compare to the hydrodynamic theory.  The experimental data agrees well with predictions from numerical methods such as in [1] and slender body theory as reported by Batchelor [2].  The theory was then used to invert the sedimentation coefficient distributions for comparison to independently measured distributions via atomic force microscopy.   Results of the measurements, comparison to the theoretical predictions and implications will be presented.

[1] M. L. Mansfield and J. F. Douglas, Macromolecules 41, 5422 (2008).

[2] G. K. Batchelor, J. Fluid Mech. 44, 419 (1970).