Electrically driven deformations of nematic gels

Abstract

The electrically driven deformations of side chain nematic networks swollen by nematic solvents (nematic gels) have been investigated. The strains of freely suspended gels between electrodes were measured as a function of field strength (E) . The deformation of the gels composed of a network and solvent with identical signs of dielectric anisotropy (Delta epsilon) is dominated by the electrically induced alignment of the nematogens. As a result, the stretching direction is variable according to the sign of Delta epsilon: The gel with positive or negative Delta epsilon is elongated parallel or normal to the field axis, respectively. The maximum strain among the samples examined is as large as 20% at E approximately equal to 0.5 MV/m. The gels composed of a network and solvent with opposite signs of Delta epsilon are compressed along the field axis since the electrostrictive effect becomes dominant because of a large reduction in the mesogen alignment effect due to the discord in the director directions of the constituent nematogens. The gels in the isotropic phase show compressive strains along the field direction in proportion to E2 purely originating from electrostriction, independently of the sign of Delta epsilon. The nematic gels are quickly deformed within a second upon field application, while the shape recovery after field removal requires a finite time on the order of 10(3) s, which reflects the structural relaxation in the polydomain texture from the oriented to the random state. The influences of elastic modulus as well as network nematicity on the electrical deformation are also examined.