Dielectric study of novel liquid crystals based on calix[4]arene Schiff bases

Novel liquid crystals based on calix[4]arene Schiff bases have been synthesised by the reaction of tetra-amino-calix[4]arene with two aldehydes (4-hydroxy benzaldehyde and 4-vanillin), further substituted with alkyl chains (n-butyl bromide and n-octyl bromide) on both the upper and lower rim by substitution of the hydroxyl groups of the calix[4]arenes. These derivatives were purified and characterised by elemental analysis and Fourier transform infrared, 1H and 13C nuclear magnetic resonance and matrix-assisted laser desorption/ionisation time of flight mass spectrometry. The compounds were investigated for liquid crystalline properties using differential scanning calorimetry, differential thermal analysis, X-ray diffraction, and polarising optical microscopy with a heating assembly. All the compounds were found to exhibit nematic structure and a typical fanlike or mosaic texture, which suggests an ordered smectic mesophase. Dielectric investigations were also carried out and showed N, SmA and SmC phases. Dielectric permittivities (ε' and ε'') were determined at a variety of temperatures (45-95°C) over a range of frequency between 20 Hz and 2 MHz.