Nematic Liquid Crystal Phases and Properties

The nematic liquid crystal phase is defined by long-range orientational order of anisotropic molecules without positional order. In its simplest uniaxial form, molecules align along a common axis known as the director, giving rise to pronounced optical birefringence and fluidity. Recent research has revealed a wealth of subphases beyond the classical nematic, including polar or ferroelectric nematics characterised by a spontaneous polarisation, twist–bend nematics exhibiting a helical modulation of the director on the nanoscale, and splay nematics defined by periodic splay deformations. These emergent phases are underpinned by subtle molecular interactions, dipolar associations and elastic instabilities, which collectively control the macroscopic properties of the fluid. The combination of fluidity, electric-field responsiveness and optical anisotropy renders nematic liquid crystals indispensable in display technologies, tunable photonics and reconfigurable optical devices. In addition, novel colloidal and curved-molecule nematics have demonstrated new opportunities for single-particle visualisation of structure and dynamics, opening pathways to advanced materials with curvature-dependent properties. The breadth of nematic phase behaviour and the fine control of director configurations promise transformative applications in quantum photonics, soft robotics and beyond.

Research from Nature Portfolio

Recent studies have demonstrated the versatility of ferroelectric nematic liquids for advanced photonic applications. Electric-field-tunable spontaneous parametric down-conversion has been implemented in ferroelectric nematic media, achieving broadband entangled photon-pair generation with efficiencies comparable to standard nonlinear crystals. Control over emission rate and polarisation state is realised by modest electric fields or by twisting the molecular director, introducing reconfigurable quasi-phase matching through molecular twist patterns. In parallel, polarisation patterning in ferroelectric nematic films has been achieved via flexoelectric coupling. Photopatterned alignment layers define splay structures that geometrically prescribe the local polarisation direction, enabling periodic polarisation lattices and guided polarisation pathways. These advances underscore the potential of polar nematics for nonlinear optics, quantum light sources and programmable photonic structures.

Nematic Liquid Crystal Phases and Properties publication trend

The graph below shows the total number of articles in nematic liquid crystal phases and properties across all publications each year (not limited to Nature Index journals).

Technical terms

Nematic phase: A liquid crystal state with long-range orientational order of rod-like molecules but no positional order, producing anisotropic optical and mechanical properties.

Director: The unit vector indicating the average alignment direction of molecules in a nematic phase.

Ferroelectric nematic: A polar nematic subphase exhibiting a spontaneous, switchable electric polarisation aligned with the director.

Twist–bend nematic: A nanoscale helical modulation of the director in which the molecular axis follows a heliconical trajectory, resulting in chirality from achiral molecules.

Flexoelectric coupling: A phenomenon in liquid crystals where deformations of the director field (splay or bend) induce bulk polarisation and vice versa.

Spontaneous parametric down-conversion: A nonlinear optical process in which a pump photon splits into a pair of lower-energy entangled photons within a nonlinear medium.

References

1. Tunable entangled photon-pair generation in a liquid crystal. Nature (2024).
2. Polarization patterning in ferroelectric nematic liquids via flexoelectric coupling. Nature Communications (2023).
3. Walking Ferroelectric Liquid Droplets with Light. Advanced Materials (2023).
4. Liquid crystals from curved colloidal rods: waves, twists and more. Reports on Progress in Physics (2024).
5. Splay Nematic Phase. Physical Review X (2018).
6. Understanding the twist-bend nematic phase: the characterisation of 1-(4-cyanobiphenyl-4′-yloxy)-6-(4-cyanobiphenyl-4′-yl)hexane (CB6OCB) and comparison with CB7CB. Soft Matter (2016).