Diffusiophroesis-controlled separation of a colloid-electrolyte suspension under gravity and solvent evaporation

Unidirectional drying a colloidal suspension has been used widely for manufacturing microstructured materials, such as ceramics, electrodes, and photonic crystals. Recent experiments and simulations demonstrated significant impacts of gravity on the phase separation process. However, in the process, the role of colloid transport induced by an electrolyte concentration gradient, a mechanism known as diffusiophoresis, is unexplored to date when coupled with gravity. In this work, we utilize direct numerical simulations and develop a macrotransport theory to analyze the advective-diffusive transport of an electrolyte-colloid suspension in a unidirectional drying cell under gravity and diffusiophoresis. We report two new significant findings. First, our simulations and theory demonstrate new scalings for the growth of the colloidal layer, where the layer produced with solute-repelled diffusiophoretic colloids could be an order of magnitude thicker than with non-diffusiophoretic colloids. Second, our results show that the enhancement in the growth of the colloidal layer due to diffusiophoresis can be achieved not just on Earth under normal gravity but also in space under microgravity. Our results enable tailoring the separation of colloid-electrolyte suspensions by tuning the interactions between the solvent, electrolyte, and colloids under Earth's and microgravity, which is central to ground-based and in-space applications.