INTERFEROMETRIC DETERMINATION OF ELECTROOPTICAL EFFECTS IN LIQUID-CRYSTALLINE BLUE PHASES

In cholesteric liquid crystals with high chirality up to three thermodynamically stable blue phases (BPI, BPII and BPIII) occur in a narrow temperature range below the isotropic phase. The BP I and BPII are characterized by a three-dimensional helicoidal structure of cubic symmetry with lattice constants of the order of several hundred nanometers. An applied electric field causes a i) change of the BP lattice constants (electrostrictive effect) and ii) a field-induced birefringence (electrooptical effect). At high fields, new field-induced phases with different symmetries compared to the zero field blue phases were observed. To get further informations about the molecular arrangement within the blue phases, the electrooptical effect has been studied with a modified microscope-interferometer in BPs of systems with positive and negative dielectric anisotropy. For the first time an electrooptical effect has been observed also in field-induced blue phases.