Spontaneous Symmetry Breaking and Linear Electrooptic Response in the Achiral Ferronematic Compound

A compound with the constituent non-chiral molecules, DIO, known to exhibit three nematic subphases namely N, Nx and NF, is studied by polarizing microscopy as function of the alignment layers on one of the substrates, no alignment on any of the substrates, alignment layer on both substrates with parallel and antiparallel rubbing, different cell spacings. The cell with one alignment layer is also studied by electro-optics. N is found to be a conventional nematic phase, but it shows two additional unusual features: chiral domains of opposite chirality and the linear EO response to the applied signal under certain experimental conditions. The emergence of chiral domains is explained by a segregation of the stable helical conformers of the opposite chirality, these preferring to form chiral domains, each with optical rotation power of ± 4o/μm. This is the first example of helical segregation observed in non-chiral molecules in the high temperature nematic phase. The conformers are suggested to arise from the rotations of the aromatic rings either left-handed or right-handed. Unlike the ordinary nematic liquid crystalline phase, linear electrooptical response to the applied electric field (i.e. to its fundamental frequency) is observed, this confirms the polar nature of this phase. The NF is the ferroelectric nematic as reported previously. The strong polar azimuthal surface interaction energy in NF phase stabilizes a homogeneous structure in planar aligned LC cells rubbed parallel and in cell rubbed antiparallel, it gives a twisted structure. The transmission spectra simulated using Berreman’s 4 x 4 matrix method for different cell conditions and for different angles between the Polarizer and the Analyzer quantitatively confirm the twisted structures in antiparallel rubbed cells that agree with experimental observations. The twist angle of 170o is found between the directors from the top to the bottom in antiparallel rubbed cells as opposed to 180o observed previously.