Two columnar phases of bent-core molecules have been observed, with a two-dimensional (2D) structure modulated in the plane perpendicular to the direction of the spontaneous polarization vector. The phases are switchable under an applied electric field, contrary to the commonly observed 2D modulated B1 phase. These new phases are built from broken smectic layers with orthogonal or tilted molecules. The evidence for a 3D structure in which the density modulations along and perpendicular to the spontaneous polarization vector co-exists is also given.

No abstract

In recent years there are several reports showing that bent-core mesogenic molecules are able to form biaxial nematic phase in which molecular rotation around the long molecular axis is strongly hindered. The x-ray pattern with azimuthally split signals at low angle region of diffraction is usually given as evidence for the biaxial nematic phase. We show experimentally and theoretically that such x-ray pattern is due to the local smectic- C fluctuations ("cybotactic" groups) in the uniaxial nematic phase.

No abstract

No abstract