ABSTRACT
The coupling of rubber elasticity with orientational order is one of the most important characteristics of liquid crystal elastomers (LCEs). This coupling effect strongly correlates the macroscopic shape with the orientational order, and results in unique stimuli-response behavior of nematic elastomers [1,2].A change in orientational order caused by external fields such as temperature variation and light irradiation drives a macroscopic deformation. Electric field is also an external field that can switch the director of liquid crystal (LC) molecules [3]. The director of many low-molecularmass LCs (LMMLCs) is readily realigned by low electric fields because of their large dielectric anisotropy and nematic interaction. The resultant significant change in optical birefringence (electro-optical effect) leads to various industrial devices, such as, LC displays.What happens in nematic elastomers under electric fields?We expect not only electro-optical effect but macroscopic deformation induced by mesogen realignment because nematic elastomers behave as solids without flowing due to the cross links. Para-electric nematic elastomers in the neat state, however, need unusually high electric fields to exhibit a finite distortion because their high elastic moduli act as a strong resistance to dielectric forces [4]. Swelling of nematic elastomers by some
appropriate LMMLCs reduces the network modulus with neither decreasing dielectric anisotropy nor nematic interaction [5]. Several studies observed a finite distortion in such swollen nematic elastomers under moderate electric fields [6-11]. Some other researchers examined the electro-optical effects in the nematic networks formed in the cells in the presence of large quantities of LMMLCs [12-14]. However, none of them observed the simultaneous optical and mechanical effects under electric fields. In the present paper, on the basis of our recent results, we review (1) the role of the signs of dielectric anisotropy of the mesogens in electrical deformation; and (2) the simultaneous electro-optical and mechanical effects observed in swollen nematic elastomers under unconstrained geometry.
