Ultra-slow capillary rise on hydrogel surfaces

Capillary rise occurs when a thin tube contacts a liquid, which rises against gravity due to the capillary force. This phenomenon is present in a wide range of everyday and industrial settings and provides the means to measure the physical properties of liquids. Here, we report on the unusual ultra-slow capillary rise on a solid-like material of agarose hydrogels. The observed meniscus motion cannot be described with classical capillary rise models, and we develop a new model based on the fluid transport through the porous hydrogel network. Our model is in good agreement with the temporal scaling observed in our experiments with agarose gels made with five different concentrations and with two different viscosities of the liquid flowing inside the gel. Our results provide a non-invasive technique to directly estimate the permeability of hydrogel interfaces with high spatial resolution, which is important in the implementation of hydrogels in advanced biomedical applications.