Freely Suspended Nematic and Smectic Films and Free-Standing Smectic Filaments in the Ferroelectric Nematic Realm

TL;DR

This paper demonstrates the creation of stable, freely suspended ferroelectric nematic and smectic liquid crystal films and filaments, revealing unique textures and structures stabilized by electrostatic interactions, expanding the understanding of liquid crystal architectures.

Contribution

It introduces new free-standing liquid crystal films and filaments from ferroelectric nematic and polar smectic phases, showcasing their unique textures and stability mechanisms.

Findings

N_F films exhibit smectic-like parabolic focal conic textures.

SmZ_A and SmA_F films show layers normal to surfaces with distinct textures.

Filaments are stable, free-standing, and have layers normal to the axis.

Abstract

We show that stable, freely suspended liquid crystal films can be made from the ferroelectric nematic ($\mathrm{N_F}$) phase and from the recently discovered polar, lamellar $\mathrm{SmZ_A}$ and $\mathrm{SmA_F}$ phases. The $\mathrm{N_F}$ 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 $\mathrm{SmZ_A}$ and $\mathrm{SmA_F}$ 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 $\mathrm{SmZ_A}$ 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 $\mathrm{SmA_F}$ films showing a texture of plaquettes of uniform in-plane orientation where both bend and splay are suppressed, separated by grain boundaries. The $\mathrm{SmA_F}$ 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.