Sensitivity Analysis of a Simulated Hydrogel

Abstract

Crosslinked polyelectrolytic polymers embedded in an aqueous solution, so-called hydrogels, show stimuli-responsive behaviour under various kinds of stimulation. These "smart" reactions can be triggered by e.g. chemical, electrical, mechanical or thermal stimuli. The hydrogels react via uptake or delivery of mobile ions and solvent, and show enormous swelling capabilities. This behaviour can be used for chemo-electro-mechanical energy converters or as an actuator or sensor. The presented research investigates anionic hydrogels in the framework of a sensitivity analysis, by a design of experiment (DOE) with the use of ANSYS optiSLang. The hydrogel itself is modelled within a finite element code (Abaqus Unified FEA) as a user element. The applied stimuli are of different nature: chemical, electrical, mechanical and thermal. On the one hand, the stimulus is applied by the change of boundary conditions, e.g. for chemical stimulation by a change of the concentrations of the constituents themselves (N a + and Cl −). For electrically stimulated hydrogels, two electrodes are incorporated at the boundaries and the electric potential is changed. On the other hand, the mechanical stimulus is defined by prescribed displacements at a boundary of the fixed hydrogel. The thermal stimulus is applied over the whole domain in the form of transient temperature changes with temperature-dependent material parameters. The reactions of the hydrogel differ-depending on the type of hydrogel and the stronger or weaker sensitivity-on the applied stimulus. The fully coupled three-field description of the chemo-electro-mechanical model enhanced with thermal dependencies is capable of giving local concentrations, electric potential and displacements.