Actuation of Dielectric Elastomer
When a voltage is applied across the electrodes, the electrostatic forces produced by the opposite free charges squeeze and the volume conservation forces the polymer to expand transversely to the applied electric field. The pressure on the polymer film due this electrostatic force is known as Maxwell stress  and can be expressed as $P=\epsilon E^2$. $E$ is applied electric field which can be written as $E=V/z$. $V$ is applied voltage and $z$ is the thickness of the material, $\epsilon$ is the permittivity of dielectric material.
Fig 1. Working principle of DE Sample
Preparation of sample
Preparation of sample involves pre-straining the DE sample and electrode coating. Different samples have been prepared each having pre-strain values 100x103, 161x162, 195x200, 250x259, 300x317, 300x287 coated with carbon-grease electrode. The steps involved in preparation of sample are as follows.
 R Pelrine, R Kornbluh, Q Pei and J Joseph, "Highspeed Electrically Actuated Elastomers with strain greater than 100%", Science, vol 287, pp 836-839, 2000.