Critical splay fluctuations and colossal flexoelectric effect above the nonpolar to polar nematic phase transition

Abstract

The recent discovery of nematic liquid crystals with polar order (ferroelectric) has created immense interest. Despite intensive research, several physical properties of this liquid crystal are yet to be investigated and understood. Here, we report experimental studies on the surface alignment, birefringence, and flexoelectric coefficient of a polar nematic $({N}_{\mathrm{F}})$ liquid crystal. Our experiments directly reveal that the splay fluctuations influence the birefringence several degrees above the nonpolar $(N)$ to polar nematic $({N}_{\mathrm{F}})$ phase transition temperature, and the heat capacity exponent obtained from the tilt angle fluctuations is close to the value reported in adiabatic scanning calorimetry measurements. The flexoelectric coefficient of the nonpolar nematic phase shows a power-law dependence on temperature. It demonstrates a strong polar coupling of pretransitional ferroelectric fluctuations with the field. These results are important for applications as well as for understanding all pretransitional effects in ferroelectric nematic liquid crystals.