Effect of hydrophobicity on colloid transport during two-phase flow in a micromodel

Abstract The goal of this research was to investigate the difference in behavior of hydrophilic and hydrophobic colloids during transport in two-phase flow, in general, and their attachment and remobiliza-tion characters, in particular. Experiments were performed in a hydrophobic polydimethylsiloxane (PDMS) micromodel. Water and fluorinert-FC43 were used as the two immiscible liquids. Given the fact that PDMS is a hydrophobic material, fluorinert was the wetting phase and water was the nonwetting phase in this micromodel. As model colloids, we used hydrophilic polystyrene carboxylate-modified microspheres (dis-persible in water) and hydrophobic fluorous-modified silica microspheres (dispersible in fluorinert) in sepa-rate experiments. Using a confocal laser scanning microscope, we directly observed fluid distribution and colloid movement within pores of the micromodel. We also obtained concentration breakthrough curves by measuring the fluorescent intensities in the outlet of the micromodel. The breakthrough curves during steady-state flow showed that the colloid attachment rate is inversely related to the background saturation of the fluid in which the colloids were dispersed. Our visualization results showed that the enhanced attach-ment of hydrophilic colloids at lower water saturations was due to the retention at the fluorinert-water interface and fluorinert-water-solid contact lines. This effect was observed to be much less in the case of hydrophobic colloids (dispersed in fluorinert). In order to explain the colloids behavior, we calculated inter