A frustrated phase driven by competition among layer structures

Using our designed ternary system consisting of a semiperfluorinated smectic liquid crystal and two nematic liquid crystals, we investigated their phase transition behaviour using polarizing optical microscopy, differential scanning calorimetry and X-ray diffraction. A mixture containing 20 mol% of the semiperfluorinated compound was found to exhibit the following unusual phase sequence: isotropic liquid - isotropic liquid + smectic A phase - nematic phase - unidentified frustrated phase (X) - modulated phase (Y) - modulated phase (Z). The frustrated phase showed a fan-shaped texture characteristic of a smectic phase, but no peak corresponding to the layer spacing was detected. No difference was found in the shearing stress between the high-temperature N phase and the frustrated phase, but electro-optical switching observed in the N phase was not detected in the frustrated phase. We discuss how the molecules organize the unusual phase transition behaviour.