(550g) Diffusiophroesis-Controlled Separation of a Colloid-Electrolyte Suspension Under Gravity and Solvent Evaporation

Unidirectional drying of a colloidal suspension has been used widely for manufacturing materials, such as colloidal coatings. In this talk, we employ direct numerical simulations to analyze the advective-diffusive transport of a colloid-electrolyte suspension in a unidirectional drying cell under the influence of solvent evaporation, gravity, and diffusiophoresis. Solvent evaporation generates a flow to concentrate the colloids and electrolyte at the drying interface. The difference in the density between the colloids and the solvent induces a gravity-driven backflow that drives the suspension away from the drying interface. In addition, the concentration gradient of electrolyte near the drying interface could impact the colloid distribution drastically via diffusiophoresis. We report two new findings focusing on the impact of diffusiophoresis. First, when diffusiophoretic interactions between the colloids and solute are attractive, diffusiophoresis could significantly enhance the concentration of colloids near the drying interface and the magnitude of the gravity-driven backflow. Second, when diffusiophoretic interactions between the colloids and solute are repulsive, diffusiophoresis could weaken or even eliminate the focusing of colloids near the drying interface and the backflow, regardless of the density-difference between the colloids and the solvent or, equivalently, the strength of gravity. Our results enable systematically tailoring the separation of a colloid-electrolyte suspension by tuning the interactions between the solvent, electrolyte, and colloids under Earth’s or microgravity, which is central to ground-based and in-space manufacturing.