A theory of large deformation in soft active materials

Soft active materials have many important applications. We develop a theory of large deformation in a family of soft active materials known as dielectric elastomers. We show that the Maxwell stress is not applicable to deformable dielectrics in general, and that the effect of electric field on deformation is material specific. Based on available experimental data, we construct for a class of model materials, which we call ideal dielectric elastomers, a free-energy function comprising contributions from stretching and polarizing. We show that the free-energy function is typically non-convex, causing the pull-in instability of dielectric elastomers.