Engineered Nanoparticles for Hydrocarbon Dectection in Oil-Field Rocks
Authors: Berlin Jacob M. , Yu Jie , Lu Wei , Walsh Erin E. , Zhang Lunliang , Zhang Ping , Chen Wei , Kan Amy T. , Wong Michael S. , Tomson Mason B. , Tour James M. 
Published: September 2011

Abstract
Polyvinyl alcohol functionalized oxidized carbon black efficiently carries a hydrophobic compound through a variety of oil-field rock types and releases the compound when the rock contains hydrocarbons.
The transport of small hydrophobic organic molecules through porous media has been studied for many years. In isolation, these hydrophobic molecules sorb very strongly to nearly all types of soil. However, it has been observed that these hydrophobic chemicals disperse more broadly in the environment than would be expected based on their strong affinity for binding to soil (Baker, 1986). One possible explanation for this behavior is that organic macromolecules, which possess amphiphilic characteristics, may sequester the hydrophobic small molecules and facilitate their transport by carrying them within the macromolecule (McCarthy, 1989; Enfield, 1988). Laboratory scale experiments have demonstrated this effect, with some cases, such as the use of β-cyclodextrin, showing highly efficient transport of a variety of hydrophobic aromatic molecules through soil (Brussea, 1994; Magee, 1991). However, selective release of the transported cargo has not been reported and β-cyclodextrin only forms 1:1 inclusion complexes with its hydrophobic cargo.
Recently, a new class of compounds, nanomaterials, has been investigated for transport through porous media. Nanomaterials are defined as having at least one dimension of less than 100 nm, and they possess a much larger surface area relative to traditional polymers used for the transport of hydrophobic cargo. Nanomaterials are expected to have significantly different transport behavior in porous media as a result of their larger size and more rigid shape as compared to polymers, and the design of nanoparticles (NPs) with efficient subsurface transport is an ongoing challenge. Nanomaterials prepared from a variety of precursors, including carbon, iron and silica, have varying abilities to flow through porous media. Water-dispersible aggregates of [C60]fullerenes can flow through sand samples and glass beads, although the breakthrough of the fullerenes is very low at early pore volumes and gradually increases over time (Wang, Y., 2008; Li, 2008). The use of a water-soluble fullerene derivative, as opposed to the water-dispersible aggregates, showed improved breakthrough for a column of glass beads (Lecoanet, 2004). Single-walled carbon nanotubes (SWCNTs), which are also prone to aggregation, show limited breakthrough in porous media (Jaisi, 2009). Reducing the SWCNTs ability to aggregate by wrapping them with a surfactant or binding humic acid to them improves their mobility in porous media (Wang, P., 2008). Similar behavior has been observed for silica and iron, as functionalization of the particles with a hydrophilic polymer, either polyethylene glycol (PEG) or carboxymethyl cellulose, reduces their affinity for aggregation and improves their transport through porous media (Lenhart, 2002; Rodriguez, 2009; He, 2009; Saleh, 2007).