  Plasticized poly(vinyl chloride) (PVC) is a jelly-like soft dielectric
material that attracted substantial interest recently as a new type of
electro-active polymers. Under electric fields of several hundred Volt/mm, PVC
gels undergo large deformations. These gels can be used as artificial muscles
and other soft robotic devices, with striking deformation behavior that is
quite different from conventional dielectric elastomers. Here, we present a
simple model for the electro-activity of PVC gels, and show a non-linear effect
of free ions on its dielectric behaviors. It is found that their particular
deformation behavior is due to an electro-wetting effect and to a change in
their interfacial tension. In addition, we derive analytical expressions for
the surface tension as well as for the apparent dielectric constant of the gel.
The theory indicates that the size of the mobile free ions has a crucial role
in determining the electro-induced deformation, opening up the way to novel and
innovative designs of electro-active gel actuators.
