Phase diagram and electro-optical Kerr effect of nematic mixtures containingtolane and biphenyl cores

Abstract

An experimental phase diagram for two types of nematic liquid crystals and their binary mixtures was established by polarised optical microscopy and differential scanning calorimetry methods. The mixtures comprised a tolane-base liquid crystal, 4-heptyl-3-fluoro-4-isothiocyanatotolane (7TOLF), and a biphenyl-base nematogen, 4-heptyl-3-fluoro-4-isothiocyanatobiphenyl (7BF). The static Kerr effect and third-order non-linearity were investigated for 7TOLF and 7BF and their nematic mixtures within the isotropic phase. Both the compounds have a positive and large Kerr constant. The second-order phase-transition temperatures, T∗, were determined for these mixtures. The linear dependence of (T - T∗)^− 1 on the Kerr constant is found to be in good agreement with the predications of the Landau–de Gennes model. The third-order non-linear susceptibility,χ⁽³⁾, values were determined for these mixtures.

Keywords:

• liquid crystals
• nematic mixture
• electro-optic Kerr effect
• pre-transition behaviour