New actuation modes of composite dielectric elastomers

The typical actuation mode of a dielectric elastomer membrane subjected to an electric field across its thickness is in-plane expansion. We show that, by selecting properly the contrast between phases (i.e. shear moduli and permittivity ratios), a hierarchical laminate may display longitudinal contraction when actuated in the same way. In particular, simple and second rank laminates are investigated. The latter performs in general better; however, we provide a guideline on how to optimize the microstructure to limit the values of the contrast parameters at which the new 'non-conventional' mode becomes available. As the requirements in terms of permittivity ratio of the two phases are somewhat extreme, we review the availability of materials that have been processed so far to assess the viability of such composite devices.