Electric-field induced deformation and bending in nematic elastomer strips with orientation gradient

Highlights

• Electric-field induced bending occurs in nematic elastomers with orientation gradient.

• Bending shapes strongly depend on the orientational distribution of the director.

• Analytical and finite element solutions for the bending behavior are obtained.

• Bending curvature is enhanced by adjusting the linearly varying director distribution.

• Bending curvature can be increased by > 300% of that of the splay-bend sample.

Abstract

Swollen nematic elastomers can deform under an applied electric field due to the electro-opto-mechanical coupling effect. This unique coupling mechanism causes the nematic elastomer to exhibit larger deformations under weak electric fields as compared to many conventional dielectric elastomers. Further, the electric-field induced deformations can be controlled by proper design of the initial liquid crystal director. Based on a simple electro-mechanical-director coupled model under small strain assumption, finite element simulations are conducted for beam-shaped thin strip samples with orientation gradient initially. Approximate analytical solutions are obtained for the electric potential, director reorientations, stress, and strain under weak electric fields. Using the first- order shear strain beam theory, the analytical solutions for the bending deflections are determined for beams with various boundary conditions, and they are only governed by the spontaneous curvature and the average transversal spontaneous shear resulting from the spontaneous strains induced by the applied electric fields. Optimization of the electric-field induced bending curvature leads to linearly-varying director distributions, which have much larger bending curvatures than that exhibited by the most commonly studied splay-bend distribution. Moreover, we demonstrate that bending shapes strongly depend on the orientational distribution of the director. Thus, a proper design can be used to effectively control the electric-field induced deformation and bending. Overall, we believe that our study is potentially useful to create desired and optimized bending for electrically-triggered sensors and actuators.