Coupled chemo-electro-mechanical formulation for ionic polymer gels -: numerical and experimental investigations

Polyelectrolyte gels consist of a network of crosslinked polymers with attached electric charges and a liquid phase. Variations of the chemical milieu surrounding the gel or application of an external electric field lead to a change in the swelling ratio of the gels. This phenomenon may be used for contraction and relaxation of chemo-electro-mechanical actuators and in particular of artificial muscles. In this paper electrically stimulated polymer gels, placed in a solution bath, are investigated. For these gels, we present a volume- and surface-coupled chemo-electro-mechanical multi-field formulation. This formulation consists of a convection-diffusion equation describing the chemical field, a Poisson equation for the electric field and a mechanical field equation. The model is capable to describe the local swelling and deswelling of ionic polymer gels as well as the ion concentrations and the electric potential in the gel and in the solution. A chemo-electric simulation is performed for a gel fiber at a given electric field; the anionic and cationic ion concentrations as well as the electric potential inside and outside the gel are computed for a given number of bound anionic groups. The resulting increase in the concentration differences on the anode side of the anionic gel can be considered as an indicator for a higher swelling ratio of the gel fiber. Mechanical and electrical measurements on anionic polyelectrolyte gels are in good agreement with the numerical results. This demonstrates the validity of the employed numerical model. (C) 2003 Elsevier Ltd. All rights reserved.