Observation of a uniaxial ferroelectric smectic A phase

Abstract

We report the observation of the smectic A F , a liquid crystal phase of the ferroelectric nematic realm. The smectic A F is a phase of small polar, rod-shaped molecules that form two-dimensional fluid layers spaced by approximately the mean molecular length. The phase is uniaxial, with the molecular director, the local average long-axis orientation, normal to the layer planes, and ferroelectric, with a spontaneous electric polarization parallel to the director. Polarization measurements indicate almost complete polar ordering of the ∼10 Debye longitudinal molecular dipoles, and hysteretic polarization reversal with a coercive field ∼2 × 10 5 V / m is observed. The SmA F phase appears upon cooling in two binary mixtures of partially fluorinated mesogens: 2N/DIO, exhibiting a nematic (N)–smectic Z A (SmZ A )–ferroelectric nematic (N F )–SmA F phase sequence, and 7N/DIO, exhibiting an N–SmZ A –SmA F phase sequence. The latter presents an opportunity to study a transition between two smectic phases having orthogonal systems of layers.

Lowering of Electrostatic Actuator Driving Voltage and Increasing Generated Force Using Spontaneous Polarization of Ferroelectric Nematic Liquid Crystals

“…[ 37 ] SmZ A was an unidentified mesophase but was classified here based on a previous study. [ 46 ] The sample was a slightly viscous fluid without elasticity. The breakdown voltage was about 15 MV m −1 .…”

Nano-clustering mediates phase transitions in a diastereomerically-stabilized ferroelectric nematic system

“…Under this circumstance, the control of the phase sequences involving the N F emergence and the successful way of stabilizing N F remain ambiguous despite huge efforts on the design and development of new N F LC molecules based on molecular parameters. Note that a newfound ferroelectric state, that is, a uniaxial ferroelectric smectic A (SmA F ) phase 37,38 that appears just below the N F phase, just emerged, offering an important clue. SmA F looks highly correlated with the N F phase; hence, the smectic cluster floating in the N F media may influence the N F phase characteristic.…”

Ferroelectric nematic liquids with conics

“…The fine structure should include "space-charge electric double layer", i.e., two parallel sheets of positive and negative space charges produced by the increase of the projection of P onto ν 1 midway across the DW, when the polarization bends from P 1 to P 2 , Fig. 4d, as discussed by Pattanaporkratana 48 for m = −1 disclinations in ferroelectric smectic C and by Chen et al 49 for parabolic walls induced by air bubbles in planar N F cells. Even for relatively low polarizations, if one neglects the screening effects of ions, mutual attraction of these sheets is expected to reduce the width of director reorientation dramatically, down to ~10 nm 48 ; ionic screening would expand this width.…”

“…We thank Noel A. Clark for illuminating discussions and for sharing Refs. 48,49 and Kamal Thapa for the help in the experiments. This work is supported by NSF grant ECCS-2122399 (O.D.L.…”