(526e) Diffusiophoresis in Porous Media Saturated with Electrolytes

Diffusiophoresis refers to the deterministic colloidal motion induced by a solute concentration gradient. Recent experiments demonstrated diffusiophoresis in porous media, but existing theories cannot predict the observed colloid motion. In this work, using regular perturbation method, we develop a mathematical model that can predict the diffusiophoretic motion of a charged colloidal particle in a porous medium driven by the concentration gradient of a general mixture of electrolytes. The porous medium is modeled as a Brinkman medium with a constant Darcy permeability. We report three key findings. First, we present that our model predictions match quantitatively with experimental measurements without fitting parameters. This highlights the predictive power of the model. Second, we demonstrate that decreasing the porous media permeability reduces the particle mobility. However, such a reduction can be compensated by using an electrolyte with a larger ion diffusivity ratio. Third, we show that the direction of the particle motion in porous media can reverse by varying the composition of an electrolyte mixture. This demonstrates the tunability of diffusiophoretic motion. The mathematical model developed here can be employed to tailor diffusiophoretic transport in porous media, which are central to applications such as nanoparticle drug delivery and enhanced oil recovery.