Dielectric Properties of Ferroelectric Liquid Crystals with Diversified Molecular Structure

Mesomorphic, thermodynamic, electro-optic and dielectric properties of three homologues of fluorosubstituted esters are described. Full chemical names of these compounds are as follows: (S)-(+)-4-(1-metylheptyloksy)benzoate-(6-pentafluoropropanoynloxyhex-1-oxy)-biphenyl-4-yl (in short 2F6BBiOC8), (S)-(+)-4-(1-metylheptyloksy)benzoate-(6-nonafluoropentanoyloxyhex-1-oxy)-biphenyl-4-yl (in short 4F6BBiOC8), (S)-(+)-4-(1-metylheptyloksy)benzoate-(6-tridecafluoroheptanoyloxyhex-1-oxy)-biphenyl-4-yl (in short 6F6BBiOC8). The compounds exhibit ferroelectric smectic C* phase between crystalline and isotropic phase. Only one compound (6F6BBiOC8) shows antiferroelectric phase (SmC(A)*) observed by dielectric spectroscopy, but the range of this phase is narrow of about 2 degrees. All three compounds exhibit in the SmC* phase Goldstone mode and Maxwell-Wagner relaxation hidden in the conductivity contribution at low frequencies, whereas in the SmC* A phase two antiferroelectric modes (AFM1) and (AFM2) contribute to the dielectric spectrum. The compounds were studied using differential scanning calorimetric, frequency domain dielectric spectroscopy, and reversal currents method to determine spontaneous polarization.