Modeling of dynamic hydrogel swelling within the pore space of a porous medium

Aim of this work is to model a multiphasic porous material modified with a hydrogel made from a granulate of Superabsorbent Polymers (SAP). The void space of the material is simultaneously filled with two interacting phases, namely a chemically active hydrogel and a multi-component aqueous pore fluid. The hydrogel has the ability to absorb and retain large amounts of the pore fluid. Depending on the pore fluid chemistry, the hydrogel is also able to reverse the absorption process by releasing absorbed solution. The overall material is finally classified as a functional porous material since the macroscopic material properties depend on the interaction within the pore space. For instance, swelling of the hydrogel within the pore space changes the morphology of the porous media and influences the hydraulic permeability and the mechanical stiffness. Absorption and desorption processes are modeled in a thermodynamic-consistent framework, while constitutive equations for mass transfer are proposed in accordance to polymer chemistry. Experiments have been carried out and inherent model parameters are identified by a Monte-Carlo method. The predicted results of the derived model are in good accordance to experimental findings. Through the reversibility of the phase transition process, the material becomes an excellent candidate of a functional porous media, e. g. a sophisticated filter, which adapts its hydraulic permeability to the pore fluid chemistry.