Evaporation-induced diffusiophoretic transport of colloidal particles in chemical solutions

The complex interactions between solute and colloids often cause heterogeneity in a colloid mixture as the solvent evaporates, which can negatively affect the microstructure of the dried film. In this work, we experimentally investigate drying-induced transport of colloidal particles suspended in solutions consisting of either ions (NaCl) or non-adsorbing polymers (dextran). Ion and polymer gradients established near the air-water interface upon evaporation give rise to the diffusiophoretic motion of colloidal particles. In the ionic solution, ion gradients drive particle motion either toward or away from the interface, depending on the surface charge of the particles. On the other hand, in polymeric solution, the repulsive particle-polymer interactions cause particles to migrate away from the interface, leading to the formation of a particle depletion zone near the interface, which is sensitive to the polymer size, concentration, and drying rate. Our results highlight the underlying impact of diffusiophoresis on dispersion drying, which has a direct influence on the quality of manufacturing of slurry-based thin films, such as porous membranes, battery electrodes, and solar cells.