Enhanced dielectric properties and alignment behavior of ferroelectric nematic liquid crystals in the non-polar nematic phase.

Abstract Ferroelectric nematic liquid crystals (FNLCs) combine long-range orientational order with macroscopic polarization. While their ferroelectric nematic phase has attracted considerable attention, the extent to which its polar character influences the non-polar nematic phase is not yet fully understood. Here, we investigate the non-polar nematic phase of the ferroelectric nematic mixture (MIX NF-P1) that emerges above 44 $$^\circ$$ C. In particular, we determine this liquid crystal interaction with alignment substrates by characterising the pretilt and polar anchoring. The pretilt is found to decrease with increasing temperature, while the polar anchoring remains strong throughout the non-polar nematic phase. Through dielectric and optical characterization, we also extract the dielectric coefficients, birefringence, voltage threshold, and the splay and bend elastic constants as a function of temperature. The voltage threshold is shown to be up to 20 times lower than in the conventional nematic liquid crystal E7, because the large dielectric anisotropy is retained in the non-polar nematic phase. The birefringence monotonically decreases with increasing temperature, while the elastic constants show temperature dependent behaviour consistent with trends reported for other FNLCs. This behavior differs markedly from those observed in conventional nematics, with the splay elastic constant remaining relatively constant. Thus, we demonstrate that the nematic phase of FNLCs cannot be regarded as a conventional nematic state and instead retains signatures of the underlying polar interactions. The combination of strong dielectric response and a low threshold voltage highlights the potential of these materials for high-speed electro-optic and photonic applications.