Comparison of the dielectric properties of 4-(2-methylbutyl)-4′-cyanobiphenyl (5*CB) and 4-pentyl-4′-cyanobiphenyl (5CB) in the liquid state

Dielectric relaxation studies of chiral 4-(2-methylbutyl)-4′-cyanobiphenyl (5*CB) in the liquid state at temperatures up to ca. 90 K above the melting point have been performed. Two experimental techniques were used: time domain spectroscopy (TDS) and an impedance analyser, which together cover the frequency range from 10 kHz to ca. 3 GHz. The obtained relaxation times τis as a function of the temperature were compared with those obtained recently for the isotropic phase of 4-pentyl-4′-cyanobiphenyl (5CB), being a typical liquid crystalline substance. It was found that for 5*CB, unlike 5CB, the relaxation time τis(T) shows a non-Arrhenius behaviour in the range of ca. 70 K above the melting point. The τis(T) behaviour was analysed using the Vogel–Fulcher–Tammann (VFT) formula. The VFT curve fits very well the experimental points as well as those obtained recently by Massalska-Arodż etal. in the supercooled state of 5*CB. For both substances the static permittivity εs was measured up to 365 K and the Kirkwood correlation factor g=µapp2/µ2 was established. The temperature dependence of g-factors indicates that the antiparallel dipole–dipole associations are stronger for the chiral compound than for the non-chiral one.