Water imbibition through hydrogel-coated capillary tubes*

We study the dynamics of water flow through hydrogel-coated capillary tubes. Hydrogel particles are widely used to absorb water in hygienic products, drug delivery systems, and microfluidic devices. Since hydrogels absorb water with volume expansion, water flow through a porous structure composed of hydrogel particles results in a deformation of the interconnected pore structure. To understand the dynamics of water flow through hydrogel particles, we examined water flow through hydrogel-coated capillary tubes as a model system. We experimentally measured the flow speed in the tube and the water volume absorbed by the hydrogel layer coated on the inner surface of the tube. The experimental observations were explained by a hydrodynamic model developed for capillary flow, taking into account the deformation of the tube wall as well as water absorption into the tube wall. Our study provides new insights into capillary flow through various hygroscopic soft porous media, including porous structures composed of hydrogel particles.