Diffusio-osmosis of surfactant solutions: molecular modeling and interfacial physics

Presenter: Huajie Zhang, Mechanical Engineering

Authors: H. Zhang, E. Ahmed, M.A. Rahman, R. Qiao

Abstract: Diffusio-osmosis is an important transport mechanism at the micro/nanoscale, with applications such as chemical injection-based enhanced oil recovery. Here, we investigate the diffusio-osmosis of surfactant solutions, a class of diffusio-osmosis where solutes are mainly contact adsorbed on walls. We compute the diffusio-osmosis using molecular dynamics simulations and delineate the limitations of classical continuum models in predicting such transport. Our model surfactants have tail groups more wall-affine than heads. In dilute solutions, the strength of diffusio-osmosis is concentration-independent and is enhanced when tail groups interact more strongly with solid walls or when head groups become smaller. As the surfactant concentration increases beyond a critical value, the strength of diffusio-osmosis decreases, initially rapidly and then slowly with increasing surfactant concentration. The classical continuum model for diffusio-osmosis can predict these trends, but quantitative discrepancies exist. They mainly stem from two interfacial effects neglected in those theories: loss of flow driving force due to the intermittent adsorption of surfactants on walls and interfacial viscosity deviating from bulk values due to the formation of surfactant nanostructures near walls.