Transport of colloids around solute-releasing hydrogel posts

Mass transfer from cylindrical or spherical bodies in fluid flow is a classical problem in physicochemical hydrodynamics that has predominantly been explored theoretically. However, experimental validation of these theoretical models remains limited. Hydrogels, which can partition and gradually release solutes, provide a versatile platform for rigorously testing existing models and uncovering novel insights. In this study, we fabricate hydrogel posts with arbitrary cross-sectional geometries in situ within microfluidic channels, generating sustained solute gradients that drive phoretic transport of colloids. By precisely characterizing solute concentration fields and colloid distributions downstream of the hydrogel posts, we systematically explore mass transport phenomena at high Péclet numbers. Our experimental findings are validated through numerical simulations and comparisons with self-similar analytical solutions for solute concentration fields. Additionally, we present new self-similar solutions for colloid distribution fields and discuss how variations in hydrogel cross-sectional shape affect solute flux and colloidal transport patterns.