Electromechanical elongation of nematic elastomers for actuation

In classical electrostriction the Maxwell stress caused by the charging of electrodes attached to a solid's surfaces causes contraction along the field direction and hence elongation in the two directions in the plane of the electrodes. We discuss the opposite possibility, that is where a nematic elastomer (the working solid) would shrink in the plane and lengthen along the field direction. The mechanism is by electrically induced rotation of the nematic director which determines the long dimension of the elastomer. Theory finds such a non-classical response only if the dielectric anisotropy exceeds the shape anisotropy, whereupon the Maxwell stress is overcome by the reduction in energy on redirecting the solid's most polarisable direction along the applied field. We thereby suggest an alternative to the usual electrostrictive actuation paradigm in that in-plane contraction arises. (C) 2008 Elsevier B.V. All rights reserved.