Stimuli-sensitive hydrogels are polymeric materials, which are able to reversibly swell in water in response to evironmental changes. Relevant stimuli include variations of pH, temperature, concentration of specific ions etc. Stacked layers composed of multiple thin hydrogels - also referred to as hydrogel-layer composites - combine the distinct sensing properties of different hydrogels. This approach enables the development of sophisticated microfluidic devices such as bisensitive valves or fluid-sensitive deflectors. In order to numerically simulate the swelling of a polyelectrolyte hydrogel in response to an ion concentration change the multifield theory is adopted. The set of partial differential equations - including the description of the chemical, the electrical and the mechanical field - are solved using the Finite Element Method. Simulations are carried out on a two-dimensional domain in order to capture interactions between the different fields. In the present work, the ion transport is governed by diffusive and migrative fluxes. The distribution of ions in the gel and the solution bath result in an osmotic pressure difference, which is responsible for the mechanical deformation of the hydrogel-layer composite. The realized numerical investigation gives an insight into the evolution of the displacement field, the distribution of ions and the electric potential within the bulk material and the interface between gel and solution bath. The predicted behavior of the relevant field variables is in excellent agreement with results available in the literature.
Polyelectrolyte hydrogels are ionic gels with viscoelastic properties. They are able to reversibly swell and deswell in response to different external stimuli. In the present work stacked layers of hydrogels - also referred to as hydrogel layers - under chemical stimulation are numerically investigated. For this, a set of coupled partial differential equations describing the chemical, the electrical and the mechanical field is solved by using the finite element method. The swelling behavior of the hydrogel layers - obtained by a novel approach for the osmotic pressure - is in excellent agreement with other investigations available in the literature.