Ferroelectric Liquid Crystalline Materials Research Articles

Ferroelectric Nematic-Isotropic Liquid Critical End Point

A critical end point above which an isotropic phase continuously evolves into a polar (ferroelectric) nematic phase with an increasing electric field is found in a ferroelectric nematic liquid crystalline material. The critical end point is approximately 30 K above the zero-field transition temperature from the isotropic to nematic phase and at an electric field of the order of 10 V/μm. Such systems are interesting from the application point of view because a strong birefringence can be induced in a broad temperature range in an optically isotropic phase.

Running streams of a ferroelectric nematic liquid crystal on a lithium niobate surface

ABSTRACTSessile droplets of a ferroelectric nematic liquid crystalline material were exposed to surface electric fields produced by pyroelectric and photogalvanic (photovoltaic) effects in X-cut iron-doped lithium niobate crystals. The resulting dynamic processes were monitored by polarisation optical (video)microscopy (POM). During heating/cooling cycles, at first, the droplets change their shape from spherical to extended ellipsoidal. Then, they start to move rapidly along the surface electric field, i.e. along the crystal’s polar axis (c-axis). During this motion, several droplets merge into running streams (tendrils) extending towards the edges of the top surface area. Finally, practically all liquid crystalline material is transported from the top surface to the side surfaces of the crystal. At stabilised temperatures, laser illumination of the assembly causes dynamic processes that are localised to the illuminated area. Also, in this case, the LC droplets merge into several tendril-like formations that are preferentially oriented along the c-axis of the crystal. The pattern of tendrils fluctuates with time, but it persists as long as the illumination is present. In this case, the LC material is transported between the central and the edge regions of the illuminated area.

New Ferroelectric Liquid Crystalline Materials with Properties Suitable for Surface Stabilized and Deformed Helix Effects

New Ferroelectric Liquid Crystalline Materials with Properties Suitable for Surface Stabilized and Deformed Helix Effects

Fabrication of Ferroelectric Liquid Crystal Thermistor

Thermistor is fabricated using thermotropic ferroelectric liquid crystalline material. The design, performance, and characteristics of this fabricated liquid crystal (LC) device are demonstrated in this article. As a representative case, the characteristics of two ferroelectric LCs (FLCs), which exhibit positive and negative temperature coefficients of resistance, are detailed. An ambient temperature ferroelectric mesogen (S)-1-[4’-(octyloxy carbonyl) phenyl]-4-[2-chloro-(4-benzamido acetyl) phenyl propionato]-Benzoate yielded negative temperature coefficient thermistor, while dextro tartaric acid with p-n decyloxy benzoic acid ferroelectric mesogen was used as a positive temperature coefficient (PTC) thermistor. This endeavor was not reported in the literature, where thermotropic mesogens are being used for thermistor [PTC and negative temperature coefficient (NTC)] application. This thermistor possesses a wide temperature range (~69° C) with a resolution of $0.05~\mu $ AV−1 and accuracy of ±0.1 °C which is more competent than its conventional counterpart. Furthermore, the heat capacity of the LC-based thermistor device is 0.2 Jg−1 K−1 for PTC and 0.4 Jg−1 K−1 for NTC.

Phase Contraction, fluorescence quenching and formation of topological defects in chiral smectic C matrix by Cd0.15Zn0.85S/ZnS core/shell quantum dots dispersion: Faster electro-optic response for gadget displays

ABSTRACT Cd0.15Zn0.85S/ZnS core/shell quantum dots (CSQDs) of size 7.54 ± 0.99 nm in diameter were prepared via gram-scale one-pot synthesis method and dispersed in a ferroelectric liquid crystalline (FLC) material into two different concentrations. Spectroscopic, electro-optical (E-O) and morphological characterisations of aforementioned composites have been carried out. CSQDs cause a significant contraction in the width of chiral smectic C (SmC*) mesophase that has also been theoretically verified. Diffusion–controlled processes are responsible for the fluorescence quenching in the FLC/CSQDs composites which has been explained by using the Stern–Volmer quenching equation. The mesomorphic investigation has revealed that helical deformation takes place in the FLC/CSQDs composites, due to which the temperature-dependent gradual growth of ferroelectric domains is noticed. The perturbed helical geometry evinces a new structure-property correlation having a molecular switching time of 135 μs that is 51% faster response as compared to the pristine system. Resultant spontaneous polarisation in the matrix of FLC/CSQDs composites is diminished because of the induced homeotropic and flexoelectric contributions. The faster E-O response and optical imaging are the fascinating features of the FLC/CSQDs composites that can probably be utilised in gadget displays.

Design of functional multicomponent liquid crystalline mixtures with nano-scale pitch fulfilling deformed helix ferroelectric mode demands

Design of new functional smectic liquid crystalline mixtures possessing polar behaviour remains quite highlighted task as those materials are highly requested by industry for specific applications in photonics. This work is devoted to specific practical method devoted to design of functional multicomponent ferroelectric liquid crystalline (FLC) mixtures based on chiral components exhibiting the ferroelectric and antiferroelectric polar order. The self-assembling behaviour, tilt angle, spontaneous polarization as well as dielectric properties of the prepared mixtures have been studied and discussed. The three resulting mixtures exhibit a broad range of the ferroelectric smectic phase, very low melting point, short helical pitch (below 180 nm) and relatively high tilt angle (about 40 degree). Excellent chemical stability and compatibility of components as well as moderate values of spontaneous polarization add another great deal to these FLCs materials for application in deformed helix ferroelectric mode in photonics and opto-electronics.

Modeling of electro-optic characteristics in vertically aligned deformed helix ferroelectric liquid crystals

New areas of application in the realms of fast phase modulators are stimulating fundamental studies in ferroelectric liquid crystalline materials. Investigation of temperature effect on light transmittance in vertically aligned deformed helix ferroelectric liquid crystal cell is the focus of our study. A fairly linear Kerr constant temperature dependence for two ferroelectric liquid crystal mixtures was analyzed by using linear regression analysis. The key result of this paper represents light transmittance dependencies as a function of squared electric field for a certain temperature range. We also report that strongly pronounced Kerr constant temperature dependence results in several temperatures with 2[Formula: see text] and higher phase modulation for the given electric field. The physics of change in light transmission plots has been analyzed.

Study of the electrocaloric effect in ferroelectric liquid crystals

ABSTRACTElectrocaloric effect (ECE) in two ferroelectric liquid crystalline (FLC) materials has been evaluated by mean of two indirect characterization methods: the photopyroelectric (PPE) technique and the polarization current reversal one. The obtained results show a good correspondence of the adiabatic temperature change associated with the ECE evaluated from both methods. This validates the possibility to use the PPE technique to investigate the ECE in FLCs. This study also demonstrates that FLCs can be used as electrocaloric material. More particularly, it shows that as for their solid homologous, liquid crystals displays more pronounced ECE in the vicinity of a first order transition than that measured near to second-order one.

Tuning the electro-optic and viscoelastic properties of ferroelectric liquid crystalline materials

This work deals with determination of the viscoelasticity coefficient in chiral smectic liquid crystals possessing the helical structure and is the continuation of the work, in which the elasticity coefficient was presented [Phase Transitions 89 (2016) 368]. The measurements have been performed using optical detection in the small deformation limit. The viscosity coefficient was measured on two commercially available pure chiral materials, namely, 4-(n-hexyloxy phenyl)-1-(2-fuethyl butyl) biphenyl-4-carboxylate and 4-(2-methylbutyl) phenyl-4-n-octylbiphenyl-4-carboxylate, and on resulting binary mixture composed from those materials in 50:50 weight ratio. All three liquid crystalline materials exhibit a tilted ferroelectric phase over a reasonably broad temperature range. Each of the two pure liquid crystalline materials have its own disadvantages. However, by design of the binary mixture in definite weight concentration, we tried to improve the behavior and to tune the properties; specifically, the effect of the viscoelastic properties on the mixture composition has been established.

Thermodynamic, optical and switching parameters of a ferroelectric liquid crystalline material having SmA*-SmC*-SmBh* phase sequence

ABSTRACTThermodynamic and electro-optical characterization of a ferroelectric liquid crystalline material, namely ((S) (+) 4-(1-methylheptyloxy) phenyl 4′-octyloxybiphenyl-4-carboxylate) possessing paraelectric SmA*, ferroelectric SmC*, hexatic SmBh* and SmI* phases has been carried out. Phase identification has been done by optical and thermodynamic studies. Switching parameters viz. spontaneous polarization, switching time and rotational viscosity have been determined. The spontaneous polarization has been found to increase with decreasing temperature in SmC* phase. The switching time is found of the order of few milliseconds.

Dual photoluminescence and charge transport in an alkoxy biphenyl benzoate ferroelectric liquid crystalline–graphene oxide composite

GO has been dispersed in a ferroelectric liquid crystalline material to prepare a FLC–GO composite.

Relaxation phenomena of a highly tilted ferroelectric liquid crystalline material (S)-(+)-4′-(3-pentanoyloxy prop-1-oxy)biphenyl-4-yl-4-(1-methylheptyloxy)benzoates

Titled ferroelectric liquid crystalline material (in short, 4H3R) exhibits cholestric (N*), ferroelectric (SmC*) and hexatic (SmB*) phases, when it is cooled from isotropic liquid phase to crystal phase. Dielectric studies have been carried out in the frequency range of 1 Hz to 35 MHz under planar anchoring conditions of the molecules. The soft mode relaxation due to the amplitude fluctuation of the polarisation vector has appeared in the N* phase, whose relaxation frequencies decrease but dielectric strength marginally increases (~0.30–0.54) with decrease in the temperature. The Goldstone relaxation mode has appeared in SmC* phase with a constant relaxation frequency. The relaxation frequency of hexatic SmB* phase follows Arrhenius behaviour. The conductivity of the material is also measured in all the exhibited phases.

Dielectric characterisation of a ferroelectric liquid crystalline material having SmA*–SmC*–SmBh* phase sequence

Thermodynamical, optical and dielectric characterisation of a material possessing ferroelectric SmC* and hexatic SmB* phases has been carried out. Phase identification has been done by miscibility studies. From the dielectric studies, a relaxation mechanism is observed in the low MHz region of the SmA* phase, which is related to the tilt fluctuation (soft mode) of the directors. In the SmC* phase, another collective relaxation mechanism has been observed in the kHz region, which is related to the phase fluctuation (Goldstone mode) of the directors. In the SmBh* phase, 2-weak relaxation modes are observed in the kHz and MHz frequency range, respectively, due to individual molecular rotations.

Synthesis and characterization of ferroelectric liquid crystalline organosiloxanes containing 4-(4-undecanyloxy bi-phenyl-1-carboxyloxy)phenyl (2S,3S)-2-chloro-3-methylvalerate and 4-(4-undecanyloxybenzoyloxy)biphenyl (2S,3S)-2-chloro-3-methylvalerate.

A series of new organosiloxane ferroelectric liquid crystalline (FLC) materials have been synthesized, and their mesomorphic and physical properties have been characterized. Four new disiloxanes and trisiloxanes, containing biphenyl 4-hydroxybenzoate and phenyl 4-hydroxybiphenylcarboxylate as mesogenic units and eleven methylene unit as spacers and (2S,3S)-2-chloro-3-methylvalerate unit as chiral end groups. The molecule, using three phenyl ring as a mesogenic unit, formulates much wider liquid crystalline phase temperature ranges than that of a two phenyl ring unit. The phenyl arrangement differences of mesogenic unit result in the greater differences of the liquid crystal phase formation. The siloxane molecule induction is helpful to the more regular smectic phase formation and smectic phase stabilization, such as chiral SC (SC*) and SB phases. The siloxane molecule is helpful to reduce the phase transition temperature and broaden the liquid crystal temperature range of the SC* phase and, simultaneously, it will not induce chain crystallization phenomenon and dilute the Ps value. The synthesis and characterization of the new FLCs materials, which exhibit a room temperature SC* phase and higher spontaneous polarization are presented.

Effect of alkyl chains length on properties of ferroelectric liquid crystals with the keto group attached to the molecule core

In order to contribute to better understanding of the molecular structure–physical property relationship, properties of ferroelectric liquid crystalline materials derived from the lactic acid with the keto group in the molecular core have been studied. These compounds differing only by the length of the chiral and non-chiral alkyl chains exhibit the paraelectric SmA* and the ferroelectric SmC* phases over 150 K broad temperature range down to the room temperature. Temperature dependences of spontaneous polarization, tilt angle, layer spacing, helix pitch length and dielectric permittivity have been compared and discussed for all studied compounds. The effect of the alkyl chains length on mesomorphic properties has been established and discussed in comparison to that of similar materials.

Synthesis and Characterization of Ferroelectric Liquid Crystalline Siloxanes Containing 4-Hydroxyphenyl(2S,3S)-2-Chloro-3-Methylvalerate

New series of organosiloxane ferroelectric liquid crystalline materials have been synthesized, and their mesomorphic and physical properties have been characterized. These new series contain bis-siloxane or tris-siloxane unit attached to the flexible alkyl chain end of (2S,3S)-2-chloro-3-methylvalerate. The siloxane molecule induction is helpful to the chiral smectic C (SC*) formation and chiral SC* stabilization, and it simultaneously causes the liquid crystal temperature range of chiral SC* to be broader. The siloxane member is helpful in reducing the smectic C (SC) transation shift temperature, and the molecule containing tris-siloxane units shows better effect than the bis-siloxane one. The synthesis and characterization of the new FLCs materials which exhibit SC* phase at room temperature and higher spontaneous polarization are presented.

A study of a ferroelectric organosiloxane liquid crystal with a high spontaneous polarisation

The dielectric permittivity, the pyroelectric coefficient and the smectic layer thickness of a novel ferroelectric organosiloxane liquid crystalline material 12KN5DSi were measured as functions of the temperature and the bias electric field in the orthogonal and tilted phases of the material. It was found that this material has a very high spontaneous polarisation (∼240 nC/cm2) in the smectic C* (SmC*) phase and also demonstrates an unusual behaviour of the pyroelectric coefficient and the smectic layer thickness in a temperature range just below the phase transition from the smectic A* (SmA*) phase. This unusual behaviour is interpreted in terms of the new statistical theory based on order parameters of the SmC* phase.

Effect of the chiral chain length on structural and phase properties of ferroelectric liquid crystals

Studies of structural and phase properties obtained on several ferroelectric liquid crystalline materials with 2-alkoxypropionate group used as a chiral centre and without any lateral substitution are presented. In dependence on the chiral chain length these compounds exhibit the cholesteric N* phase, the ferroelectric smectic C* and a low-temperature SmX phase. Values of the spontaneous polarization and spontaneous tilt angle have been determined within the whole range of the SmC* phase. A low-temperature SmX phase has been identified as the orthogonal hexatic SmB* phase. The molecular parameters, namely the layer spacing in the SmC* and SmB* phases and the average intermolecular distances (D) between neighbouring parallel molecules in all investigated phases have been determined using the results of the X-ray diffraction obtained on non-oriented samples. The effect of the chiral chain length on mesomorphic, structural and physical properties of the studied ferroelectric liquid crystalline materials is discussed.

Electro-optic switching and dielectric spectroscopy studies of ferroelectric liquid crystals with low and high spontaneous polarization

Electro-optic and dielectric studies have been carried out on two ferroelectric liquid crystalline materials: namely, the commercial mixture possessing low spontaneous polarization and pure material with high spontaneous polarization on cells with planar alignment. The calculated values of spontaneous polarization, response time and rotational viscosity were found ~ 240 nC/cm 2, 20 nC/cm 2, 1600 μs, 500 μs, 230 kg/ms and 19 kg/ms for high and low polarization ferroelectric liquid crystalline materials, respectively. For the ferroelectric liquid crystal with high polarization, the effect of temperature, frequency and bias field on the dielectric properties have been studied and the obtained results were compared to those obtained on the ferroelectric liquid crystalline mixture with low spontaneous polarization.

Gradual phase transition between the smectic-C*and smectic-CA*phases and the thresholdless antiferroelectricity

We have constructed the phase diagrams for a binary-mixture system of antiferroelectric and ferroelectric liquid-crystalline materials in both thick and thin cells. In the phase diagrams the boundary between the smectic- C and smectic- C{A} phases runs almost parallel to the temperature axis below from ca. 70 degrees C down to at least -25 degrees C . The SmC-SmC_{A} phase transition for a thin cell shows a large supercooling, and a gradual transition occurs near the boundary. Moreover, the thin cell shows a continuous evolution from the antiferroelectric to the ferroelectric state by increasing the electric field applied across the cell. The continuous evolution seemingly reflects the phenomenon of thresholdless antiferroelectricity. In order to explain these phenomena and in clarifying the mechanism of the so-called frustration between ferroelectricity and antiferroelectricity, we have measured the interlayer interaction energy by varying the constituent concentrations in the binary-mixture system. The measured interlayer interaction close to the boundary indicates that the gradual phase transition and continuous evolution result from the suppression of the solitary-wave propagation by the effect of surfaces.