Drying Dynamics of Hydrogels

The swelling of deformable porous media, like hydrogels, has been widely investigated for several decades. In contrast, their drying dynamics have received far less attention despite their pivotal importance for coatings, geomechanical processes, and even the functioning of plants. In this study, we combine 3D visualization using confocal microscopy with macroscopic measurements of drying hydrogel layers to elucidate the underlying physics. Our direct measurements of the internal hydrogel strain reveal that it is not homogeneous, in stark contrast to common assumptions. Instead, the rapid formation of a dry crust produces a spatially-varying permeability (k) and Young’s modulus (E). Leveraging our measurements, we propose a modified drying model that quantitatively captures the measured drying rate over a broad range of temperatures and relative humidity.