Electrostriction of BPI and BPII for blue phase systems with negative dielectric anisotropy

The deformation of liquid crystalline blue phases BPI and BPII under the influence of a weak electric field is studied for systems with negative dielectric anisotropy. For the initially cubic structures of these materials, the interplanar spacings in the field direction were found to increase or to decrease in the field, depending on the orientation of the unit cell. In this paper, Kossel diagrams of the deformed structures are presented. By the reported experiments, the electrostriction tensor describing small distortions of the lattice in the electric field can be determined completely. For two mixtures, numerical values of the electrostriction coefficients are given.