Homogeneous deposition of particles by absorption on hydrogels


When a drop containing colloidal particles evaporates on a surface, a circular stain made of these particles is often observed due to an internal flow toward the contact line. To hinder this effect, several approaches have been proposed such as flow modification by addition of surfactants or control of the interactions between the particles. All of these strategies involve the liquid phase while maintaining the drying process. However, substitution of evaporation by absorption into the substrate of the solvent has been investigated less. Here, we show that a droplet containing colloidal particles deposited on swelling hydrogels can lead to a nearly uniform coating. We report experiments and theory to explore the relation between the gel swelling, uniformity of deposition and the adsorption dynamics of the particles at the substrate. Our findings suggest that draining the solvent by absorption provides a robust route to homogeneous coatings.