Polyelectrolyte gels are ionic electroactivematerials. They have the ability to react as both, sensors and actuators. As actuators they can be used e.g. as artificial muscles or drug delivery control; as sensors they may be used for measuring e.g. pressure, pH or other ion concentrations in the solution. In this research both, anionic and cationic polyelectrolyte gels placed in aqueous solution with mobile anions and cations are investigated. Due to external stimuli the polyelectrolyte gels can swell or shrink enormously by the uptake or delivery of solvent. In the present research a coupled multi-field problem within a continuum mechanics framework is proposed. The modeling approach introduces a set of equations governing multiple fields of the problem, including the chemical field of the ionic species, the electrical field and the mechanical field. The numerical simulation is performed by using the Finite Element Method. Within the study some test cases will be carried out to validate our model. In the works by Gülch et al., the application of combined anionic-cationic gels as grippers was shown. In the present research for an applied electric field, the change of the concentrations and the electric potential in the complete polymer is simulated by the given formulation. These changes lead to variations in the osmotic pressure resulting in a bending of different polyelectrolyte gels. In the present research it is shown that our model is capable of describing the bending behavior of anionic or cationic gels towards the different electrodes (cathode or anode).
Hydrogels are viscoelastic active materials. They consist of a polymer network with bound charges and a liquid
phase with mobile anions and cations. In water based solutions these gels show large swelling capabilities under
the influence of different possible stimulation types, such as chemical, electrical or thermal stimulation.
In the present work a coupled chemo-electro-mechanical formulation for polyelectrolyte gels using the Finite
Element Method (FEM) is applied. In addition to the three given fields, the dissociation reactions of the bound
charges in the gel are considered. Thus, we are able to model and simulate pH-stimulation and to give the
different ion concentrations, the electric potential and the mechanical displacement. Depending on the initial
conditions and the dissociation ratio, different kinds of stimulation cycles can be simulated.
Concluding, the developed model is applicable for chemical stimulation and can model both, hydrogel actuators
and sensors.
Polyelectrolyte gels show adaptive viscoelastic characteristics. In water-based solutions they have enormous
swelling capabilities under the influence of various possible stimulation types, such as chemical, electrical or
thermal. In the present work a fully coupled 3-field formulation for polyelectrolyte gels using the Finite Element
Method (FEM) is applied. This formulation consists of a chemical, electrical, and mechanical field equation. The
mechanical field is coupled to the chemo-electrical field by a prescribed strain stemming from an osmotic pressure
term. In experiments it has been proven that there is a large dependency between the applied temperature and
the actual swelling degree of the gel. In the present research, the thermal stimulation is investigated. First, only
the actual temperature is considered in the osmotic pressure term. Then, additionally, temperature-dependent
material parameters obtained from experimental measurements are applied. The calibration of the numerical
simulation is performed with experimental results available in literature.
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