SYNTHESIS AND CHARACTERIZATION OF NEW FERROELECTRIC LIQUID-CRYSTALS CONTAINING OLIGOMETHYLENE SPACERS

Two series of ferroelectric liquid crystals containing a phenyl biphen yl carboxylate mesogenic group and oligomethylene spacers (n = 3, 4, 6 , 8) were synthesized and characterized. The chiral moieties are the ( S)-2-methylbutoxycarbonyl and (S)-1-methylheptoxycarbonyl groups. The mesomorphic behaviours of the compounds were characterized using diffe rential scanning calorimetry and optical polarized microscopy. Spontan eous polarization (P-s) of the liquid crystals was measured by an auto mated polarization tester over a wide temperature range. The mesomorph ic properties are discussed as a function of spacer length and positio n of the chiral centre. It is found that the phase transition temperat ure decreases with increasing number of oligomethylene units. The phas e behaviours of the LC with (S)-1-methylheptoxycarbonyl, are more comp lex than those with (S)-2-methylbutoxycarbonyl, due to the flexible ta il in the former. Moreover, the spontaneous polarization depends mainl y on the position of the chiral centre, with P-s < 15 nC cm(-2) and P- s = 60 similar to 123 nC cm(-2) for the series with (S)-2-methylbutoxy carbonyl and (S)-1-methylheptoxycarbonyl groups, respectively.