Colloidal stability and dynamic adsorption behavior of nanofluids containing alkyl-modified silica nanoparticles and anionic surfactant

Abstract Nanofluids containing slightly hydrophobic silica nanoparticles have been shown to reduce surfactant adsorption on rocks in enhanced oil recovery methods. In this work, we chemically modified the surface of silica nanoparticles with two different alkyl groups (octyl and hexadecyl) to study in detail the mechanisms of interaction with anionic surfactants in nanofluids. The alkyl-modified nanoparticles showed higher colloidal stability compared to hydrophilic silica nanoparticles when dispersed in micellar solutions of sodium dodecyl sulfate, forming small, highly-charged nanoclusters. The presence of the hydrocarbon chains on the silica surface was able to significantly improve the anionic surfactant retention in solution (up to 90%), due to additional hydrophobic interactions with the surfactant tails. Results from dynamic adsorption tests using an unconsolidated porous medium showed an increase in the surfactant recovery after nanofluid injection, suggesting a fast adsorption/desorption mechanism. Therefore, the nanofluids containing alkyl-modified nanoparticles were more effective in reducing the adsorption loss, retaining the anionic surfactant in bulk and limiting the amount of free surfactant available for adsorption on the porous medium.