Calorimetric, optical and dielectric measurements on two Schiff’s based liquid crystalline materials exhibiting multiple phase transitions

We report high-resolution calorimetric, optical and dielectric studies on two Schiff’s based liquid crystalline materials, 4O.5 and 5O.5, which exhibit multiple phase transitions. The study goes beyond the commonly studied isotropic-to-nematic (I–N) and nematic-to-smectic A (N–SmA) phase transitions and explores higher-order smectic phase transitions. The critical exponent, α values, for different phase transitions has been explored. For the I–N, N–SmA, SmA–SmC, SmC–SmF, SmF–CrG and SmB–CrG transitions, α values close to 0.5 and amplitude ratios A⁻/A⁺ ~ 1.6 and D⁻/D⁺ ~ 1 indicate a first-order nature. Notably, for the SmA–SmB transition, although α (≈ 0.64) is larger than the tricritical value of 0.5, A⁻/A⁺ ~ 1.2 and D⁻/D⁺ ~ 1, and the study reports an order parameter critical exponent (β) of 0.26 ± 0.002, which supports a tricritical nature for this transition. Importantly, the ratios of A⁻/A⁺ and D⁻/D⁺ are found to have similar values across all three-measurement methods, indicating consistency and agreement among these methods.

Graphical abstract

Optical textures of the SmF and CrG phases. Temperature dependence of birefringence for compounds 4O.5 and 5O.5