Diffusiophoresis and Diffusioosmosis in Tandem: Two- and Three-Dimensional Colloidal Transport in a Dead-End Pore

Abstract

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 monovalent solute. Recent studies have considered two-dimensional geometries including dead-end pores as well as multivalent solutes 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 a multivalent solute 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. 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. Furthermore, applying the principles of Taylor dispersion, we develop a novel one-dimensional dispersion model which integrates the effects of diffusioosmosis in both two and three dimensions for arbitrary forms of diffusiophoretic and diffusioosmotic velocities; this offers physical insight regarding the diffusive spreading of particles undergoing diffusiophoresis and greatly simplifies calculations. Our dispersion model shows strong agreement with the full two-dimensional model for colloidal particle diffusivities greater than or equal to 1/100th of the characteristic diffusivity of the electrolyte. Together our full two-dimensional model and our dispersion model provide a comprehensive overview of dead-end pore particle motion in the presence of solute concentration gradients. By offering a larger toolbox to manipulate colloidal particles and measure microfluidic properties, our models can be exploited for lab-on-a-chip technologies, biophysical systems, and clean water technologies.