Ferroelectric nematic liquid crystals as a new paradigm in polar soft matter: a review

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Ferroelectric nematic liquid crystals (FNLCs) constitute a newly established and rapidly evolving class of soft materials in which long range orientational order coexists with the spontaneous macroscopic polarization (P). Unlike conventional apolar nematics (N), ferroelectric nematic (FN) phase breaks inversion symmetry, leading to exceptionally strong electro-optic (EO), dielectric, mechanical and nonlinear optical (NLO) responses at ultra-low driving fields. The present work surveys and contextualizes major experimental, theoretical and materials advances in FN, covering molecular design, phase behavior, interfacial alignment, elasticity, dielectric dynamics, NLO and emerging device concepts. Studies on highly polar rod like and bent core mesogens reveal spontaneous polarization values of 2–7 µC cm -2 , dielectric permittivity approaching 10 4 –10 5 , NLO coefficients up to ~ 25 pm V -1 and voltage controlled switching behavior. The studies also report that such behavior of FN arises from the interplay of strong dipole–dipole correlations, flexoelectric effects, coupling between polarization and director fields, elastic constant softening and electrostatic interactions at surfaces and interfaces. These properties enable transformative applications of FN in low power EO devices, photonics, actuators, adaptive optics, microfluidics and soft ferroelectric technologies. Despite the rapid progress, significant challenges remain including ionic effects, viscosity, surface anchoring control, defect management and stabilization of room temperature FN phases. Overall, FNLCs open a fundamentally new paradigm bridging soft condensed matter physics, molecular engineering and next generation functional devices.