How swelling affects hydrogel surface wettability*

Wetting behavior of hydrogels can be highly time dependent. Some studies have suggested that this time dependence is due to the water content in swollen hydrogels affecting surface properties. We investigate how this time dependence is related to the diffusion of water into the gel from the droplet. We performed time-dependent advancing and receding contact angle experiments with hydrogels of various thicknesses where we expect thicker gels to have longer time constants in their contact angle evolution. In addition, we tested whether there is a dependency of crosslinking on the time constant. The results of this study will help us to better understand problems in controlling hydrogel surface wettability and how changing involved variables in preparing gels, would improve our knowledge of hydrophilic soft materials.