Large Spontaneous Polarization Research Articles

Conoscopic study of the Scα∗ phase and the Devil's staircase in an antiferroelectric liquid crystal

Abstract The molecular orientational structure of the Scα∗ phase has been studied by means of X-ray, dielectric and conoscopic measurements for 4-(1-methylheptyloxycarbonyl)phenyl 4′-octylcarbonyloxybiphenyl-4-carboxylate. It was found by X-ray scattering that the Scα∗ phase is tilted. According to the conoscopic observation under a low field, the optic plane of Scα∗ is parallel to the field direction similar to that of the Scα∗ phase of 4-(1-methylheptyloxycarbonyl)phenyl 4′-octyloxybiphenyl-4-carboxylate. It was also found that the molecular orientation of the Scα∗ phase is antiferroelectric in the high temperature region, while in the low temperature region it is ferrielectric and changes with temperature, suggesting the so-called Devil's staircase. The critical temperature, where the biaxiality and the tilt angle of the average optic axis have maximum values, was assigned to the ferrielectric state with the largest spontaneous polarization.

Synthesis of ferroelectric liquid crystals with large spontaneous polarization

The magnitude of spontaneous polarization of liquid crystals forming chiral smectic C phases is discussed in terms of a dipole moment and rotational barrier neighbouring the chiral centre of the liquid-crystalline molecules. Using quantitative relations obtained from a molecular-orbital calculation for some compounds having polar groups such as –CO2–, –O– and –CO–, the molecular structure of a chiral dioxaborinane derivative with a large spontaneous polarization was designed; this was then synthesized and confirmed to form an Sc* phase exhibiting a large spontaneous polarization of 200 nC cm –2 as predicted.

Ferroelectric Liquid-Crystalline Polytartrate

Ferroelectric liquid crystalline polytartrate [CO-CHR-CHR-COO(CH 2 ) 4 O] n (R = O(Ch 2 ) 6 OPhN=NPhNO 2 ) was prepared by melt polycondensation and studied. Cholesteric and chiral smectic (SmC * ) phases were observed. LCPTT exhibited the large spontaneous polarization value of 5 mC/m 2 in the SmC * phase because of a stereopolar coupling of the chiral tartrate moiety.

Anomalous current and electrooptic response in a polyacrylate ferroelectric liquid crystal with large spontaneous polarization

Abstract A side-chain polymer exhibiting a chiral smectic phase was investigated. Due to its anomalous current and electrooptic responses, we discuss the possibility of antiferroelectric order in the polymer, and compare its behaviour with a low-molar mass antiferroelectric substance. In particular, we study the birefringence modulation resulting from the field induced antiferroelectric-to-ferroelectric transition, and determine the induced polarization by the field reversal method.

Synthesis and Mesomorphic Properties of Novel Ferroelectric Liquid Crystals with a Trifluoromethyl Group at the Chiral Center

Abstract A variety of ferroelectric liquid crystals with a trifluoromethyl group at the chiral center were newly synthesized utilizing optically active 3-trifluoromethylalkanoic acids prepared by optical resolution procedures. Some homologous compounds having a various length of the alkyl chain or the kind of the spacer group between the core and the chiral center were synthesized and their physical properties, particularly concerning phase behavior, spontaneous polarization, optic tilt angle and response time were evaluated. Most of these compounds exhibited chiral smectic C phase in a wide temperature range including room temperature and were found to possess a large spontaneous polarization value.

Synthesis and Properties of Optically Active 3-Aryl-5-alkyloxazolidin-2-ones. New Chiral Dopants for Ferroelectric Liquid Crystals

Abstract New chiral dopants for ferroelectric liquid crystals containing an optically active oxazolidin-2-one moiety, synthesized from (R)-1,2-epoxyoctane, exhibit large spontaneous polarization.

Optically Active Ketones with Intramolecular Hydrogen Bond

Abstract New ferroelectric liquid crystal compounds having an optically active alkanoyl group on one side and a chiral group derived from lactic acid on the other side of the core were synthesized. The new compounds with a three-ring core exhibit very large spontaneous polarization, when the signs of the spontaneous polarization due to the two chiral groups are the same. In particular, the compounds with an intramolecular hydrogen bond show larger spontaneous polarization as high as 1130 nC/cm2. The spontaneous polarization values are much greater than the sums of the spontaneous polarization for corresponding compounds having one of the two chiral groups. The dopant properties of the new compounds were also studied.

Synthesis of Fluorine-Containing Ferroelectric Liquid Crystals

Abstract Ferroelectric liquid crystals having a fluorine atom at an asymmetric carbon were synthesized by means of a new method without hydrofluoric acid. An amino acid, L-isoleucine, is converted to (R,S)-α-fluorinated chiral carboxylic acid. Biphenyl and triphenyl type liquid crystals are easily synthesized using this fluorinated carboxylic acid, which show a large spontaneous polarization of 200 nC/cm2 for the biphenyl type and 300 nC/cm2 for the triphenyl type. The electro-optic properties of the mixtures consisting of the chiral compound and various non-chiral smectic C (SmC) compounds are also described.

A New Operation Mode of a Ferroelectric Liquid Crystal Cell with an Asymmetrical Surface Condition II

A new operation mode which has two substrates with different surface interaction characteristics, a ferroelectric liquid crystal mixture with a large spontaneous polarization, a large tilt angle, and an N*·Sc* transition, is experimentally studied. Measuring optical properties of the developed cell shows that the new operation mode provides black and white images even when the cell is thick (3-6 µm).

“New Short-Pitch Bistable Ferroelectric (SBF) Liquid Crystal Displays”

We present a new type of bistable electro-optical device based on ferroelectric Sc* liquid crystals exhibiting a short pitch (0.43 µm) and a large spontaneous polarization (50150 nC/cm2). Features of the new short pitch bistable ferroelectric liquid crystal displays (SBF-LCDs) which are based on the effect are: short switching times (25 µs) at room temperature using 2 µm cell gap and 30 V bipolar pulses; contrast ratios>35; multiplexing ratios>1000; large on-state brightness due to a large memory switching angle of 40° as well as a weak temperature dependence of both, response time and memory tilt angle.

Novel Ferroelectric Liquid Crystalline δ-Valerolactone Derivatives with Very Large Spontaneous Polarization

Abstract A series of new chiral compounds with a δ-valerolactone ring were synthesized and the physical properties of these compounds as well as the electrical properties of their ferroelectric liquid crystal (FLC) mixtures were investigated. The magnitude of spontaneous polarization (Ps) in the chiral smectic C phase (SmC*) was found to be as high as 384 nC/cm2 for (2R, 5R)-2-(4′-octyloxybiphenyl-4-carboxy)-5-butyl-δ-valerolactone at ΔT = Tc - T = 5°C, where Tc is the temperature of transition from the isotropic phase to the SmC* phase and T is the temperature at which the experiments were carried out. An FLC mixture containing 2% by weight of the optical isomer, (2S, 5R)-2-(4′-octyloxy-biphenyl-4-carboxy)-5-hexyl-δx-valerolactone exhibited a response time as fast as 96 μ seconds at 25°C, for an applied square-wave voltage of ± 10 volts. The relationship between the structural properties and the thermal properties, magnitude and polarity of Ps as well as the response times for their FLC mixtures are disc...

New Ferroelectric Liquid Crystals Having 2-Fluoro-2-Methyl Alkanoyloxy Group

Abstract We have prepared ferroelectric liquid crystals with newly designed chiral part, 2-fluoro-2-methyl alkanoyloxy group. The physical properties of the ferroelectric liquid crystals having this chiral part are compared with those of other ferroelectric liquid crystals having 2-fluoro alkanoyloxy group, 2-trifluoromethyl alkanoyloxy group, 2-fluoro-2-trifluoromethyl alkanoyloxy group and 2-methyl alkanoyloxy group. The ferroelectric liquid crystals having 2-fluoro-2-methyl alkanoyloxy group show large spontaneous polarization, compared with other fluorinated ferroelectric liquid crystals. We have investigated the effect of the core structures on the spontaneous polarization. Introduction of a pyrimidine ring in the core part extremely enhances spontaneous polarization, over 400 nC/cm2. Moreover, we have also investigated the effect of chiral dopants of the compound having this chiral part.

New Short-Pitch Bistable Ferroelectric (SBF) Liquid Crystal Displays

We present a new type of bistable electro-optical device based on ferroelectric Sc* liquid crystals exhibiting a short pitch (0.43 µm) and a large spontaneous polarization (50···150 nC/cm2). Features of the new short pitch bistable ferroelectric liquid crystal displays (SBF-LCDs) which are based on the effect are: short switching times (25 µs) at room temperature using 2 µm cell gap and 30 V bipolar pulses; contrast ratios>35; multiplexing ratios>1000; large on-state brightness due to a large memory switching angle of 40° as well as a weak temperature dependence of both, response time and memory tilt angle.

Novel Temperature Dependences of Helical Pitch in Ferroelectric and Antiferroelectric Chiral Smectic Liquid Crystals

A variety of temperature dependences of helical pitch were found in ferroelectric SmC* and antiferroelectric SmCA* chiral smectic liquid crystals with large spontaneous polarization. In the vicinity of the transition temperatures of the materials showing the second-order SmA-SmC* or SmA-SmCA* phase transition, the pitch gradually increases with decreasing temperature over several degrees. In the materials which show the first-order phase transition from SmA to SmC* or to SmCA*, the maximum pitch suddenly appears at the transition. It was also confirmed in all of the materials used that the helix undergoes a discontinuous change in the pitch length and its handedness at the SmC*-SmCA* phase transition. The molecular orientational structure of the ferrielectric phase is also discussed on the basis of the temperature dependence of the pitch of (S)-MHPOBC.

フッ素置換不斉骨格をもつ強誘電性液晶の合成とその物性

In order to prepare new types of ferroelectric liquid crystals (FLC) with a large spontaneous polarization and a short response time toward electric field, optically active compounds possessing a fluorinated asymmetric frame were synthesized utilizing optically active 2-fluoroalkanols prepared from R- (+) -1, 2-epoxyalkanes, or 1, 1, 1-trifluoro-2-octanol and 3-trifluoromethylalkanoic acids prepared by the optical resolution of their racemates. The liquid crystals prepared from the above mentioned fluorinated compounds exhibited such remarkable FLC characteristics as a wide temperature range of the S*c phase, a large spontaneous polarization, and a short response time. We now wish to describe the synthetic procedures and the mesomorphic properties of these new types of FLC.

Design and synthesis of new fluorinated ferroelectric liquid-crystalline polymers

The synthesis and specific properties of the polymers derived from the monomers CH 2 =C(R)CO 2 (CH 2 ) n OPhPhCO 2 PhCO 2 CHR 1 CmH 2m+1 (R=H,Me; R 1 =CF 3 , CF 2 CF 3 ; m=6,7,8,10 n=2,6,8,12) are described. These materials exhibit quick response time (<10 ms) and large spontaneous polarization (40−70 nC/m 2 ) (90°C). A discussion of the response time−structure relationships is given. The response time becomes faster as the achiral chain connecting the mesogen to the polymer backbone and the chiral chain length becomes shorter. Especially, it is found that a trifluoromethyl group on the stereogenic center enhanced the response time

Carbon-13 nuclear magnetic resonance of ferroelectric liquid crystals with off-magic-angle spinning

The orientational ordering of three ferroelectric liquid crystals 4′-(3-methyl-2-chloropentanoyloxy)-4-alkyloxybiphenyls has been studied by 2D carbon-13 nuclear magnetic resonance (NMR) with variable angle sample spinning. The three homologs have hexyloxy (C6), heptyloxy (C7), and octyloxy (C8) chains, respectively, at the 4 position. They exhibit smectic A (SA) and chiral smectic C (S*C; ferroelectric) phases and have unusually large spontaneous polarization of the electric dipoles. In the SA phase, macroscopic alignment of the molecular director along the spinning axis can be achieved by cooling the sample rapidly from the isotropic liquid. For the S*C phase, the molecular alignment is different for the three compounds. At a magnetic field of 7.05 T, the helical structures of C6 and C8 unwind and the molecular directors align along the spinning axis at a spinning rate of 1 kHz. However, under the same conditions, the helical structure of C7 is retained and its carbon-13 NMR spectrum shows a partial powder pattern. On the other hand, the racemate of C7 has a normal smectic C (SC) phase without a helical structure, and the molecular director can be easily aligned for the NMR study. The racemate of C8 was also synthesized and studied for comparison. The 2D NMR technique used was separated local field (SLF) spectroscopy with an efficient proton–proton dipolar decoupling sequence BLEW-48 in the evolution period. The carbon–proton dipolar coupling constants were determined and the order parameters for different molecular segments of the liquid crystal were calculated. The carbon-13 chemical shifts were also measured as functions of temperature and the data were used to probe the temperature dependence of order parameters. The results show that the C–H bond at the first chiral center in these compounds has an unusually large negative order parameter. This could be due to restricted rotation of the molecular segment at the chiral center, which would be related to the high spontaneous polarization of these compounds.

The dielectric properties of DOBA-1-MPC with large spontaneous polarization

Abstract The frequency and temperature dependence of the complex dielectric constant in DOBA-1-MPC with large spontaneous polarization was investigated close to SmA-SmC phase transition. The frequencies and dielectric strengths of a Goldstone and soft mode were determined. The experimental results were compared with theoretical model; the agreement is quite good.

Electro-optic effects in a ferroelectric liquid crystal mixture

Abstract Recently Ferroelectric chiral smectic (SmC*) liquid crystals have attracted significant attention because of their possible applications as high speed switching devices.l Another electro-optic effect2 was realised by Yoshino and Ozaki in rather a thick cell, which has been termed as transient scattering mode. In the actual use of the liquid crystals, two or three compounds are generally mixed to form a new compound to suit the required conditions, viz., (1) high stability and long life, (2) large spontaneous polarization, (3) ferroelectricity at around room temperature and so on. An attempt has been made to study the electro-optic properties in a ferroelectric liquid crystal mixture, FCS101, which has a smectic C* phase in the temperature range 15-55.4°C.

Ferroelectric liquid crystals with large spontaneous polarization and high speed display devices

Abstract Ferroelectric liquid crystals with large spontaneous polarization exceeding 10-7 C/cm2 prepared by taking the following design factors into consideration are discussed; (a) separation between the chiral carbon and the dipole moment, (b) bulky molecular group connected to the chiral carbon, (c) introduction of large bond moments, (d) orientation of many bond moments around chiral carbon, (e) dipole moment between the core and chiral carbon, (f) the dipole moment at the core, and (g) the effect of hydrogen bonds. Anomalous dielectric behavior in these new ferroelectric liquid crystals and high speed response times of less than several tens of μs in electro-optic cells have also been discussed.