Mesogenic compounds belonging to the two well-known -cyanophenyl, and -isothiocyanatophenyl homologous series, which distinctly differ in the molecular polarity $(-\mathrm{C}\equiv \mathrm{N},5\mathrm{D};-\mathrm{N}=\mathrm{C}=\mathrm{S},2.5\mathrm{D}),$ show an essential difference in the pretransitional dielectric behavior in the vicinity of the isotropic to nematic (I-N) phase transition. Taking into account the results presented in Phys. Rev. E 67, 041705 (2003), the features of the I-N transition observed for the less polar mesogens are characteristic for the first order phase transition, whereas in the case of the strongly polar ones, the I-N transition is undoubtedly close to the second order.

• Received 24 September 2003

DOI:https://doi.org/10.1103/PhysRevE.69.022701