Freely suspended nematic and smectic films and free-standing smectic filaments in the ferroelectric nematic realm

• Published in: Physical chemistry chemical physics : PCCP 2024-12, Vol.27 (1), p.119-128
• Main Authors: Hedlund, Keith G, Martinez, Vikina, Chen, Xi, Park, Cheol S, Maclennan, Joseph E, Glaser, Matthew A, Clark, Noel A
• Format: Article
• Language: English
• Subjects: Ferroelectric materials; Ferroelectricity; Filaments; Grain boundaries; Liquid crystals; Motion picture directors & producers; Nematic crystals; Phases; Polarization; Thin films; X-ray scattering
• ISSN: 1463-9076; 1463-9084; 1463-9084
• DOI: 10.1039/d4cp03425b

We show that stable, freely suspended liquid crystal films can be made from the ferroelectric nematic (N F ) phase and from the recently discovered polar, lamellar SmZ A and SmA F phases. The N F films display two-dimensional, smectic-like parabolic focal conic textures comprising director/polarization bend that are a manifestation of the electrostatic suppression of director splay in the film plane. In the SmZ A and SmA F phases, the smectic layers orient preferentially normal to the film surfaces, a condition never found in typical thermotropic or lyotropic lamellar LC phases, with the SmZ A films exhibiting focal-conic fan textures mimicking the appearance of typical smectics in glass cells when the layers are oriented normal to the plates, and the SmA F films showing a texture of plaquettes of uniform in-plane orientation where both bend and splay are suppressed, separated by grain boundaries. The SmA F phase can also be drawn into thin filaments, in which X-ray scattering reveals that the smectic layer planes are normal to the filament axis. Remarkably, the filaments are mechanically stable even if they break, forming free-standing, fluid filaments supported only at one end. The unique architectures of these films and filaments are stabilized by the electrostatic self-interaction of the liquid crystal polarization field, which enables the formation of confined, fluid structures that are fundamentally different from those of their counterparts made using previously known liquid crystal phases. Freely suspended ferroelectric smectic A film viewed in reflection. Director bend and splay are both suppressed in this highly polar phase, giving a mosaic of locally uniform, block-like smectic domains separated by sharp grain boundaries.