Homogeneous deposition ofarticles by absorption on hydrogels

When a drop containing colloidalarticles evaporates on a surface, a circular stain made of thesearticles is often observed due to an internal flow toward the contact line. To hinder this effect, several approaches have beenroposed such as flow modification by addition of surfactants or control of the interactions between thearticles. All of these strategies involve the liquidhase while maintaining the dryingrocess. However, substitution of evaporation by absorption into the substrate of the solvent has been investigated less. Here, we show that a droplet containing colloidalarticles 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 thearticles at the substrate. Our findings suggest that draining the solvent by absorptionrovides a robust route to homogeneous coatings.