Effect of Stabilizer Properties on Nanoparticle Attachment in Chemically Heterogeneous Media
Greg Lowry, Robert Tilton
(Left Top) Transport Experiment Setup. (Left Bottom) Schematic of contact angle. (Bachmann et. al., 2000) (Right) Attachment efficiencies of washed PVP and GA silver.
A fundamental understanding of the mobility of nanoparticles (NPs) is needed to determine the distribution of and potential exposure risks to NPs in the environment. Studies have shown that adsorbed polyelectrolyte layers on NPs afford electrosteric repulsions and enhance the mobility of NPs in homogeneous porous media. However, in chemically heterogeneous media, the mobility of NPs may be affected by interaction between adsorbed polymer layers and hydrophobic patches on collector surfaces. In this study, we measured the attachment efficiency of polymer- and polyelectrolyte-coated NPs in chemically heterogeneous saturated porous media compared to in homogeneous media.
We used three coated silver NPs: citrate (anionic), polyvinylpyrrolidone (PVP, nonionic), and gum arabic (GA, a complex polysaccharide/glycoprotein mixture, negatively charged at a neutral pH). Mixtures of clean glass beads and octadecylichlorosilane (OTS) coated glass beads were used for modeling heterogeneous media surfaces, where OTS-coated surfaces are hydrophobic. Contact angle measurements were used to determine the degree of hydrophobicity of the OTC coated sand. The attachment efficiency of citrated silver, which is mostly determined by electrostatic interactions, was not affected by the portion of hydrophobic OTS treated glass beads, showing that electrostatic interactions are consistent regardless of the amount of hydrophobic collector surfaces. Conversely, the attachment efficiencies of PVP and GA coated silver NPs increased proportionally with an increasing fraction of hydrophobic glass beads. In addition, the presence of excess polymer in solution led to further deposition of PVP coated NPs. These results indicate that the relative hydrophobicity of the nanoparticle stabilizers governs attachment and thus, the mobility of NPs in the presence of hydrophobic patches on heterogeneous media surfaces, presumably through hydrophobic interactions. From this study, we can conclude that organic materials in the environment will influence transport of coated NPs.
This work is supported primarily by a National Science Foundation (NSF) grant through the Center for Environmental Implications of Nanotechnology (CEINT). CEINT is an entity with participants at multiple institutions, including Carnegie Mellon University.