Fyzikální ústav Akademie věd ČR

We found a unique effect of the applied electric field for new chiral liquid crystalline compound, namely lactic acid derivative. We observed reversible transformation of the planar TGBA texture to the homeotropic one, homogeneously dark in crossed polarizers. The transformation is an analogy of the Frederiks transition known in nematics and only rarely can be found for smectics. The unusual behavior of the TGBA phase under the electric field can be explained by the specific packing of molecules within the smectic layers, resulting in relatively high layer compressibility, which lowers the energy of structural defects and thus facilitates the structure transformation. The perfectly dark state of studied compounds, induced by the electric field, either stable or reversible, is appealing for specific applications. Positive dielectric anisotropy in both chiral compound and racemic mixture is detected up to the field frequency of about 10 kHz, above this frequency the anisotropy is negative.Such change of the dielectric anisotropysign, known in nematics as the dual frequency effect, might be important for photonics such as adaptive or diffractive optics [V. Novotna et al., Soft Matter 11, 4649 (2015)].

Fig. 1: The liquid crystalline texture for the racemate of the studied compound in smectic phase after the field application: the planar texture below the electrode is transformed to homogeneous and remains homogeneously dark in crossed polarizers. The original anchoring of molecules in the planar texture is marked by a white arrow and the polarizers are parallel to the edge of the photo.