Mobility of multi-walled carbon nanotubes in unsaturated porous media

A sand packed column was used to investigate the mobility of MWCNTS in unsaturated porous media under unfavorable conditions for deposition. Experiments were designed to assess water content, flow rate & grain size effect on the mobility of MWCNTs. It was found that variation in water content had no effect on mobility of MWCNTs until 16% effective saturation. Thick water film, high flow rate & repulsive force between MWCNTs & porous media made MWCNTs highly mobile. At high flow rate MWCNTs were highly mobile & their mobility decreased with decreasing flow rate. At low flow rate, slow exchange between immobile & mobile water zones made MWCNTs less mobile & increased their deposition. In both sands (D50=300-150 μm) used in this study, MWCNTs were mobile & their mobility slightly decreased in finer sands due to increase in surface area & the number of depositional sites, as well as decrease in pore water velocity. In finer sands, effects of physical straining were not observed. A comparison of different aspect ratios for MWCNTs suggested that, the aspect ratio has low impact on mobility. An increase in size due to aggregation enhances physical straining & made hydrophobic MWCNTs less mobile in an unsaturated porous media. MWCNTs breakthrough curves in coarse sand at effective saturation of a) 16% b) 36% C) 70% d) 100%. MWCNTs breakthrough curves in coarse sand at different flow rate. a) 2.5 ml/min b) 1.5 ml/min c) 0.5 ml/min