Diffusiophoresis and diffusioosmosis in tandem: Two-dimensional particle motion in the presence of multiple electrolytes

Diffusiophoresis is the movement of colloidal particles due to a gradient in the concentration of a solute. Previous studies on diffusiophoresis have focused largely on one-dimensional colloid transport due to the gradient of a single electrolyte. Recent studies have considered two-dimensional geometries including dead-end pores, multiple electrolytes, and a background flow field due to diffusioosmosis. In this work, we develop a model of the time-dependent diffusiophoretic compaction of colloids in a two-dimensional pore due to the gradient of multiple electrolytes in tandem with a diffusioosmotic slip-driven background flow field, which builds upon these recent studies by combining each of these effects. We simulate this model for varying properties of the pore walls and colloidal particles. Furthermore, we conduct experiments varying the initial ion combinations and total solute concentration, which show good qualitative agreement with the simulations. Our results indicate that diffusiophoretic compaction can be increased or decreased by manipulating electrolyte combinations, total solute concentration, wall charge, and particle diffusivity; each effect can modify the particle velocity, with varying strength, in unison or in opposition to the other effects. By offering a larger toolbox to manipulate colloidal particles, our results on diffusiophoretic and diffusioosmotic motion in tandem and in the presence of multiple electrolytes can be exploited for lab-on-a-chip and biophysics applications.