FLEXOELECTRIC POLARIZATION CHANGES INDUCED BY LIGHT IN A NEMATIC LIQUID-CRYSTAL

In a nematic liquid crystal where the director field has a splay-bend deformation mediated by the boundary conditions there is a certain int rinsic polarization density distribution characteristic of the flexoel ectric properties of the medium. By application of an electric field p erpendicular to the director, a twist is induced which is a measure of the flexoelectric anisotropy [I. Dozov, Ph. Martinot-Lagarde, and G. Durand, J. Phys; (Paris) Lett. 43, L-365 (1982)]. We show that in mole cules susceptible to a photoinduced configurational change we may chan ge the volume polarization by UV illumination and relate the change in flexoelectric coefficients to the configurational change in the molec ule. In the experiment we use the British Drug House (Merck) nematic m ixture E7 doped with 5 wt % of the dye 4-hexyloxy-(4'-hexyl)azobenzene . The photoinduced trans-cis configurational change leads to an increa se by 40% in the flexoelectric anisotropy (e(s)-e(b))/K.