Thermal and optical characterization of liquid crystal 4′-hexyl-4-biphenylcarbonitrile/4-hexylbenzoic acid mixtures

• 6BA/6CB binary mixtures were characterized.
• The smectic and nematic phases were observed.
• The nematic thermal stability increased with increasing heating rate.
• The phase transition activation energy was calculated.

We present the thermal and optical properties of binary mixtures formed from hydrogen-bonded liquid crystal 4-hexylbenzoic acid (6BA) and 4-hexyl-4′-biphenylcarbonitrile (6CB) mesogens. Phase transition temperatures and enthalpy values are evaluated by differential scanning calorimetry (DSC) and phases identified by polarized optic microscopy (POM). The experimental results obviously show that the 6BA/6CB binary mixtures exhibit nematic and smectic phases. The most interesting result is that although the smectic phase is not observed in pure components 6BA and 6CB, it is observed in their some binary mixtures. The thermal properties like phase peak temperatures, enthalpy changes and thermal span of binary mixtures are affected by depending on the mixture ratio. The nematic range increase in the binary mixture compared to the individual mesogen, and also the phase transition temperature values and the nematic thermal stability factor increase as heating rate increases. Furthermore, the calculated activation energy values show that the reorientation of the molecules during the phase transitions of the mixture occurs on an orderly basis.

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