Micromodel study on repartitioning phenomena of a strongly hydrophobic fluorophore at a colloid/1-octanol interface

[ 1] Colloids are considered as potential carriers of otherwise immobile contaminants. In this framework the contaminant-colloid interaction is assumed to be permanent, or the contaminant release from the colloids is not explicitly assessed. In this study, we report on micromodel experiments to visualize and quantify the behavior of colloids in a chemically reactive environment. Fluorescent polystyrene latex beads were injected into a micromodel pore network containing water, air, and 1-octanol. The colloids were found to attach to the hydrophobic 1-octanol phase with slightly higher attachment rates compared to the solid interface. Colloids attached to the 1-octanol sometimes disintegrated because of a swelling of the polystyrene polymer. The hydrophobic fluorescent dye was then found to partition into the 1-octanol. While the 1-octanol droplets were slowly dissolving, the fluorescent dye was staying in the droplet at first. At high concentrations and very small droplets the dye was dissolving with 1-octanol. Although one might be tempted to neglect the repartitioning of contaminants from colloids to other phases because of a limited mass of colloid associated contaminants, this effect has to be included into colloid transport models at contaminated sites with nonaqueous phase liquids, which are more attractive to the contaminant than the colloid or which change the stability of the colloid.