(276b) Single-Walled Carbon Nanotube Dynamics in Rock-Like Porous Media

Single-Walled Carbon Nanotubes (SWNTs) have unique electronic and mechanical properties that have led to an increased interest for their use in a wide range of applications (i.e., composite materials, drug delivery, and electronics). Because of their extremely high aspect ratio and slenderness (~1 nm diameter), SWNTs can increase the electrical conductivity of fluids more effectively and access much tighter spaces than other particles of equivalent volumes.  Moreover, under appropriate conditions, SWNTs precipitate into highly conductive chains that can span macroscopic length scales.¹ Therefore, SWNTs can be useful in oil reservoirs as tools for sensing, targeting and as contrast agents. Recently, we used video microscopy to observe individual SWNTs by tagging with fluorescent dyes² and individual semiconducting SWNTs by near-infrared (NIR) fluorescence.^3,4 These techniques allowed us to directly measure SWNT diffusion, bending dynamics and stiffness in aqueous media.  In addition, we studied SWNT dynamics in agarose gels, a special case of porous media mimicking biological tissues and cells, and showed how media pore size and SWNT stiffness affect diffusion.⁵ We now study diffusion and bending dynamics of individual SWNTs within a rock-like porous media as a model for oil reservoirs. Porous media is produced by packing colloidal silica particles between clean glass surfaces, where the packed layer is a few particles thick, allowing for optical imaging without index matching. We image both SWNT motion within rock-like porous media by intrinsic NIR fluorescence microscopy and the packed silica structure using transmitted light microscopy. Results are presented comparing SWNT translational and rotational diffusivity within packed silica to that previously observed in agarose gels.⁵ We find that the lower porosity and large, fixed obstacles of the silica pack versus that of agarose gels lead to highly path dependent dynamics and show how pore structure (i.e. diameter and tortuosity) affects not only SWNT diffusion but also bending mode dynamics. Ongoing work is focused on comparing measured SWNT mobility to models for anomalous diffusion based on bending energy and mean passage time.^6,7  Future work will focus on investigating the effects of surface functionalization toward controllable localization and formation of conductive SWNT networks for signaling, as well as, specific targeting of oil-water interfaces within porous media.

1.         Kamat, P. V., et. al., (2004) JACS 126, 10757

2.         Duggal, R. & Pasquali, M. (2006) PRL 96, 246101

3.         Weisman, R. B., et. al., (2004) App Phys A 78, 1111

4.         Fakhri, N., et. al., (2009) PNAS 106, 14219

5.         Fakhri, N., et. al., (2010) Science 330, 1804

6.         Odijk, T. (1993) Macromolecules 26, 6897

7.         Saxton, M. J. (1994) Biophys J 66, 394