Ferrielectric Liquid Crystal Research Articles

The Influence of Cell Thickness and Driving Voltage Shape on the Frequency Dispersions of Dielectric Characteristics of Ferrielectric Liquid Crystal

The Influence of Cell Thickness and Driving Voltage Shape on the Frequency Dispersions of Dielectric Characteristics of Ferrielectric Liquid Crystal

Broad temperature range ferrielectric liquid crystal: Temperature dependencies of dielectric and electro-optical properties

Broad temperature range ferrielectric liquid crystal mixture FerriLCM-1 was previously developed in 2022 (Pozhidaev et al. 2022). In that work dielectric and electro-optical properties of the mixture were studied at room temperature. Electrically induced birefringence index reached 0.01 at a wavelength of 532 nm with response times of 300 μs. In this paper we continue the FerriLCM-1 properties investigation in a wide temperature range from the room ones till the isotropic phase transition temperature. It is found that one of the critical electric fields is almost temperature independent, while the Kerr coefficient of quadratic electro-optical effect in deformed helix ferroelectric (DHF) mode grows with temperature increase. This leads to an increase in the depth of phase modulation. Another critical electric field decreases smoothly with temperature rising. At 47–50 °C two critical electric fields merge, while temperature dependencies of all other dielectric and electro-optical parameters of the mixture are continuous and smooth functions. At about 50 °C the maximum electrically induced birefringence in DHF-mode is ΔneffE=0.022 under the applied electric field E=0.4 V/μm and with 80 μs response time. FerriLCM-1 mixture operating in the DHF-mode exhibits a giant Kerr coefficient of 1700 nm/V2 (or even up to 2900 nm/V2 at λ=400nm) at the temperature of 85 °C combined with a 50 μs response time. This is the highest value of Kkerr coefficient among liquid crystals. All these properties make ferrielectric liquid crystal mixture FerriLCM-1 suitable for solving various problems of phase modulation of light and use in low-voltage devices.

Electro-optical effect of unpolarized light modulation in homeoplanar structures of ferroelectric and ferrielectric liquid crystals.

A clearly expressed effect of unpolarized light electro-optical modulation by homeoplanar structures of a smectic C* ferroelectric liquid crystal (FLC) and a ferrielectric liquid crystal (FerriLC) was discovered and investigated for the first time to our knowledge. This effect of electrically controlled light scattering is insensitive to the applied voltage sign, as for polymer-dispersed nematic liquid crystals (PDLCs), but the electro-optical modulation frequency reaches the kilohertz range. Occurrence conditions and essential features of the effect, as well as its physical origin, are discussed.

Ferrielectric Liquid Crystal with a Subwavelength Helix Pitch As an Electro-Optic Medium for Phase Spatial Light Modulators

Ferrielectric Liquid Crystal with a Subwavelength Helix Pitch As an Electro-Optic Medium for Phase Spatial Light Modulators

Broad temperature range ferrielectric liquid crystal as a highly sensitive quadratic electro-optical material.

A chiral smectic liquid crystal in which a ferrielectric phase with a helix pitch p0 less than 125 nm exists over a temperature range of at least from -3°C to +36°C has been developed. Such a wide temperature range (including room temperatures) of the ferrielectric phase with a subwavelength helix pitch has been achieved for the first time, to the best of our knowledge, which creates opportunities for the practical use of ferrielectric liquid crystals. A quadratic electro-optical effect caused by deformations of the helix in an electric field is observed in the ferrielectric phase, and the Kerr coefficient, which reaches almost 200 nm/V2, is significantly higher than the same coefficient for the blue phase and for the smectic C* phase, which means a higher sensitivity of the developed ferrielectric liquid crystal to the electric field. The electro-optical response time does not exceed 300μs at room temperatures for this ferrielectric liquid crystal.

Broad temperature range ferrielectric liquid crystal with subwavelength helix pitch

The ferrielectric liquid crystal (FerriLC) phase with the helix pitch po of about 100 nm was revealed in a broad temperature range from -3°C to + 35°C in a mixture containing an achiral smectic-C (SmC) biphenylpyrimidine and two non-mesogenic chiral diesters of 4,4”-terphenyl dicarboxylic acid.

PB12 Field-Induced Superlattice Structures and Effective Long-Range Interlayer Interactions in Ferrielectric Liquid Crystals

PB12 Field-Induced Superlattice Structures and Effective Long-Range Interlayer Interactions in Ferrielectric Liquid Crystals

Effective long-range interlayer interactions and electric-field-induced subphases in ferrielectric liquid crystals.

Microbeam resonant x-ray scattering experiments recently revealed the sequential emergence of electric-field-induced subphases (stable states) with exceptionally large unit cells consisting of 12 and 15 smectic layers. We explain the emergence of the field-induced subphases by the quasimolecular model based on the Emelyanenko-Osipov long-range interlayer interactions (LRILIs) together with our primitive way of understanding the frustration in clinicity using the q_{E} number defined as q_{E}=|[R]-[L]|/([R]+[L]); here [R] and [L] refer to the numbers of smectic layers with directors tilted to the right and to the left, respectively, in the unit cell of a field-induced subphase. We show that the model actually stabilizes the field-induced subphases with characteristic composite unit cells consisting of several blocks, each of which is originally a ferrielectric three-layer unit cell stabilized by the LRILIs, but some of which would be modified to become ferroelectric by an applied electric field. In a similar line of thought, we also try to understand the puzzling electric-field-induced birefringence data in terms of the LRILIs.

A field-induced ferrielectric liquid crystal phase

Understanding the structures and stability conditions of emerging liquid crystal (LC) phases brings us a step closer to the crucial understanding of delicate self-assembling nanoscale systems and the consequential impact on their macroscopic properties. We report experimental evidence and a theoretical model for a ferrielectric LC phase which has a three-layer repeat structure and is field-induced but exhibits a symmetry and electro-optical properties that are distinct from those of the known ferrielectric (SmC*FI1) phase. This discovery has implications for the ways in which LC phases are identified, and offers the potential for better control of ferroelectric LC devices.

Stable field-induced ferrielectric liquid crystal phases in devices

The field-induced transitions between ferri-, antiferro-, and ferroelectric liquid crystal phases are interesting because although there are only small thermodynamic differences between them, each of these phases has different electrical and optical properties. We report an irreversible field-induced transition from an antiferroelectric phase to the ferrielectric phase in a liquid crystal device, and compare it to a system in which the transition is reversible. The two systems differ mainly in their spontaneous polarization (120 nC cm−2 for the former and 60 nC cm−2 for the latter) while the optical tilt is comparable (29° and 25°, respectively). We explain the observed transitions based on the relative magnitudes of the discrete flexoelectric and spontaneous polarizations.

Asymmetric switching in a ferrielectric liquid crystal device

The fast multistate switching associated with ferroelectric and antiferroelectric smectic liquid crystals makes them important materials for electro-optic devices, and asymmetric electro-optic responses are of particular interest for some analog switching applications. We report intrinsic asymmetric switching in a ferrielectric liquid crystal device observed using time-resolved small angle x-ray scattering and electro-optic measurements. The experiments reveal a marked variation in the response time depending on field polarity not present in the ferroelectric or antiferroelectric phase. We suggest that this is a consequence of the ferrielectric structure itself and interactions with the device surfaces.

Discontinuous change in the smectic layer thickness in ferrielectric liquid crystals

The temperature dependence of the thickness of thick free-standing films is studied using a high-resolution film thickness measurement technique. A small discontinuity in the temperature dependence of the smectic layer thickness at every phase transition between ferro-, ferri-, and antiferroelectric phases is observed. We show that the major contribution to it arises from a change in the smectic tilt angle.

Ferroelectric and Antiferroelectric Liquid Crystals

Ferroelectric liquid crystals have been a major research topic since 30 years. However, when it comes to liquid crystals, the term “ferroelectric” is strongly ambiguous and frequently not only leads to confusion and misunderstanding but also obscures the basic concepts. The property of ferroelectricity in liquid crystals was first claimed in 1975. Five years later so-called surface-stabilized ferroelectric liquid crystals were described, which caused a surge in industrial interest because of their promising electro-optical applications, in particular for high-resolution liquid crystal displays. The industrial interest led to a considerable activity in synthesizing new compounds with the desired properties. In the course of this materials development antiferroelectricity in liquid crystals was then also sought for and was finally identified in 1989. At the same time as the first industrial ferroelectric devices (the Canon displays) came on the market in 1995, the antiferroelectric liquid crystals were being considered as even more promising for applications. In parallel, ferrielectric liquid crystal materials were announced. Moreover, in 1995, a new phenomenon, the “thresholdless antiferro-electricity” was advertised. I believe that these names indicate a certain lack of comfort in adopting terms and definitions taken from the field of solid state phenomena. Therefore, it might be adequate to question whether liquid crystal materials really qualify to be called “ferroelectric, anti-ferroelectric and ferrielectric.” My own answer to this is to an important part negative. At least, no liquid crystal so far is ferroelectric. I will review our current understanding of polar liquid crystals and contrast them to ferroelectric and antiferroelectric solid crystals. While some of the electric properties can be very similar, it is the optical properties that really make the liquid crystals interesting. In particular, the optical properties of antiferroelectric liquid crystals are surprisingly rich, as discovered only in the very last years.

STRUCTURES AND ELECTRIC FIELD EFFECTS IN FERRO-, FERRI- AND ANTIFERRO-ELECTRIC LIQUID CRYSTAL DEVICES

This paper reviews several experimental studies of electric-field effects in liquid crystal devices containing ferroelectric, antiferroelectric and ferrielectric liquid crystals. Small-angle X-ray scattering has been employed to study both rapid, reversible layer flexing and irreversible, high-field deformations in surface stabilised ferroelectric devices. New antiferroelectric materials are also considered and the tilt angle and chevron angle adopted in devices are described. Generally, the chevron angle is found to compare well with the steric tilt angle (∼20°) and is considerably lower than the optical tilt angle (∼30°). Both conventional and resonant X-ray scattering experiments have been used to probe the layer and interlayer structure and field-induced deformations in antiferroelectric, ferrielectric and ferroelectric liquid crystal devices. It is found that the mechanism of the chevron to bookshelf transition is phase-dependant and is thresholdless in the ferroelectric phases of these materials. Further, resonant scattering reveals that the field-induced antiferroelectric or ferrielectric to ferroelectric transition can occur at field strengths that are similar to or higher than those required to deform the smectic layers.

Resonant x-ray scattering study of the antiferroelectric and ferrielectric phases in liquid crystal devices.

Resonant x-ray scattering has been used to investigate the interlayer ordering of the antiferroelectric and ferrielectric smectic C* subphases in a device geometry. The liquid crystalline materials studied contain a selenium atom and the experiments were carried out at the selenium K edge allowing x-ray transmission through glass. The resonant scattering peaks associated with the antiferroelectric phase were observed in two devices containing different materials. It was observed that the electric-field-induced antiferroelectric to ferroelectric transition coincides with the chevron to bookshelf transition in one of the devices. Observation of the splitting of the antiferroelectric resonant peaks as a function of applied field also confirmed that no helical unwinding occurs at fields lower than the chevron to bookshelf threshold. Resonant features associated with the four-layer ferrielectric liquid crystal phase were observed in a device geometry. Monitoring the electric field dependence of these ferrielectric resonant peaks showed that the chevron to bookshelf transition occurs at a lower applied field than the ferrielectric to ferroelectric switching transition.

Electro-Optical Properties and its Measuring Method for a Ferrielectric Liquid Crystal

The electro-optical properties of the FELC, such as driving voltage, hysterisis, contrast, transmittance and response time, were investigated. The two times rubbed cell in polyamic acid and polyimide state showed smaller hysterisis and faster response time compared with that of the one time rubbed cell in polyimide state. The driving voltages of one time rubbed cells are almost the same regardless of the different rubbing strength. The contrast of FELC cell increased as the cell thickness decreased.

Ferrielectric liquid crystal subphase studied by polarized fourier-transform infrared spectroscopy

IR dichroism and the structure of a homogeneously aligned cell of a chiral smectic antiferroelectric liquid crystal (R)-1-methylheptyl 4-(4(')-dodecyloxybiphenyl-4-ylcarbonyloxy)-3-fluorobenzoate [with acronym (R)-12OF1M7] in a ferrielectric subphase in the temperature range between the antiferroelectric phase (also referred to as Fi2) and the smectic-C*(SmC*) phase are studied using polarized Fourier transform IR spectroscopy. The polarization dependencies of the absorbance for several characteristic bands are quantitatively analyzed for different stages of the electrically induced structural transformations in the sample, including the helix unwinding and the phase transition from the ferriphase to the SmC* phase. A qualitative similarity of the voltage dependence of the normalized angular shift of the IR absorbance profile for the "chiral" carbonyl band to that of the normalized macroscopic polarization is found. The voltage dependent dichroic properties of the sample are analyzed in terms of the molecular structure and unwinding of the helical structure under an external electric field. The rotational orientational biasing of the carbonyl groups around the long molecular axis is confirmed by the spectral data. The analysis of IR dichroic data for the field induced SmC* phase is used to determine the rotational orientational distributions for the carbonyl groups.

PAb12 V字スイッチングを示す「フェリ誘電相」の構造

PAb12 V字スイッチングを示す「フェリ誘電相」の構造

Frustration between Ferroelectricity and Antiferroelectricity in Extremely Soft Chiral Smectic-C Like Phases of Liquid Crystals

In a group of compounds that exhibit antiferroelectric and/or ferrielectric liquid crystal phases, the bent molecular shape has been considered to cause unique interactions among smectic layers. The interactions are responsible for the successive phase transitions as described by the devil's staircase and the V-shaped switching, which are related with the interlayer ordering and the diminished tilting correlation, respectively. These two are apparently contradictory each other, but result from the same cause, i.e. frustration between ferroelectricity and antiferroelectricity in the Sm-C* like phase. The ANNNI model Yamashita and Miyazima introduced has been shown to describe the frustration appropriately provided that we undertake some refinements: the Ising spin corresponding to the tilting sense of the local in-plane director, the X-Y character of the spin, the tilt angle decrease toward Sm-A, and most importantly, the reassignment of the pseudo-spin to the biasing direction of the molecular rotation about their long axis.

Symmetries and induced effects in bilayer and multilayer antiferroelectric and ferrielectric liquid crystal phases.

The stable antiferroelectric and ferrielectric smectic phases which may arise below a chiral SmA* phase are investigated theoretically. The symmetry and physical properties of the bilayer and multilayer configurations are worked out. Antiferroelectric and ferrielectric bilayer and multilayer configurations, possessing an induced spontaneous ferroelectric polarization component perpendicular to the smectic layers, are shown to take place, as the result of a nonlinear piezoelectric effect. These states of low polar symmetries occur when the angle between the inlayer projections of the dipoles and the director of the molecules is different from 90 degrees.