Electrooptics of mm-scale polar domains in the ferroelectric nematic phase

Abstract

The recent discovery of the ferroelectric nematic phase has opened the door to experimental investigation of one of the most searched liquid crystal phases in decades, with high expectations for future applications. However, at this moment, there are more questions than answers. In this work, we examine the formation and structure of large polar nematic domains of the ferroelectric nematic material RM734 in planar liquid crystals cells with different aligning agents and specifications. We observe that confining surfaces have a strong influence over the formation of different types of domains, resulting in various twisted structures of the nematic director. For those cells predominantly showing mm-scale domains, we investigate the optical and second harmonic generation switching behaviour under applications of electric fields with a special focus on inplane fields perpendicular to the confinement media rubbing direction. In order to characterise the underlying structure, the polar optical switching behaviour is reproduced using a simplified model together with Berreman calculations.

Electrically Tunable Reflection Color of Chiral Ferroelectric Nematic Liquid Crystals

“…These show that the director structure is inhomogeneous, consisting differently twisted domains at zero electric field (see Figure 2c,g). The existence of such structures was described previously by Chen et al [35] and Sebastian et al [34] The cholesteric (N*) textures of RM734 doped with 2%BDH at 150 °C are shown in the third row of Figure 2. Textures in transmission between crossed polarizers at ± 0.18 and 0 V µm −1 fields (Figure 2i,j, respectively) show reddish color.…”

“…[32,33] The large ferroelectric polarization and dielectric constant, coupled with sub-millisecond switching, offer potential applications such as high-power super capacitors and low voltage driven fast electro-optical devices. The electro-optical properties of RM734 were recently shown to depend strongly on the surface treatments of the samples, [34,35] namely that the polarity of surface anchoring may couple to the bulk polar order parameter and lead to oppositely twisted domains. To obtain a uniform texture, one needs to bias the twist by adding chiral dopants to the system.…”

Surface alignment of ferroelectric nematic liquid crystals

“…We observe that confining surfaces have a strong influence on the formation of different orientational patterns and domains 6 and show that the polar ordering appearing at the N-N F phase transition changes the interactions of the director with bounding surfaces, a key aspect of nematic LC science and its potential for technology. We demonstrate that by designing the polarity of the 2D bounding surfaces, it is possible to control the 3D structuring of P(r) in the N F phase.…”

A new order of liquids: polar order in nematic liquid crystals

“…In 2017 two materials were reported – RM734 5 and DIO 6 – that are now understood to have polar nematic order and are ferroelectric, over a century after Born's conjecture. 7–9 This so-called ferroelectric nematic (N F ) phase displays a slew of unique properties: ferroelectric properties with huge spontaneous polarisation, 8,10 polar domains, 10 strong non-linear optical response, 11 unique electrooptic responses, 12 and thermal gradient-induced circular motion of particles, 13 to name a few. The remarkable properties of the N F phase, coupled with fluidity and relative ease of alignment, 14 will ensure this field flourishes in the decades to come.…”