Ferroelectric Liquid Crystal Sample Research Articles

Enhancement of electro-optical response of photonic crystal fibers infiltrated with ferroelectric liquid crystal doped with titanium dioxide nanoparticles.

Light propagation has been studied in photonic crystal fibers (PCFs) doped with W212 ferroelectric liquid crystal (FLC) composites with titanium dioxide nanoparticles (TiO2 NPs) of low concentrations between 0.2 and 1 wt. % in the FLC matrix. Optical microscopy observations indicated a slight increase of transition temperature to the isotropic phase by ∼1-2°C compared to the undoped FLC sample, and the TiO2 admixture was found to decrease free ionic charge impurities in the FLC, thus improving its electro-optical parameters. The switching time measurements in the PLCFs clearly indicate that TiO2 NPs reduce switching times for low electric field intensity, even by 32% compared to the undoped PLCF.

Optical Rotation and Transmittance of Different Phases of Ferroelectric Liquid Crystal Sample ZLI 3654

Objectives: The Phase transition scheme of Ferroelectric Liquid Crystal (FLC) sample has been studied in a temperature range 500C to 950C. Methods: The material was procured from Merck, Germany and was used as such without any further purification, and studied for the measurement of optical rotation and transmittance. The Polarizing Optical Microscopy (POM) technique has been used and the different phases existing in the sample were observed by placing the sample having planar alignment under crossed polarizer arrangement. Findings: The sharp variation in the values of optical rotation and transmittance at the phase transition points clearly indicates that the different phases exist in the experimental sample. From the LDR vs Temperature and Optical Rotation vs Temperature study, four different phases for the sample were obtained. The SmC* phase exists in the temperature range 300C – 620C and at 620C, the SmA* occurs. The sample shows SmA* phase in the temperature range 620C – 760C and at 760C sample transit to Nematic phase which occurs in the temperature range 760C – 860C and lastly, Isotropic phase appears at 860C. Novelty: Some researchers have studied the same sample but in the temperature range 300C to 620C where they were able to observe only two initial phases namely SmC* and SmA* whereas the present study reports the four different phases (SmC*, SmA*, nematic and isotropic) of the Ferroelectric Liquid Crystal (FLC). The same study can also be carried out using the other technique like Differential Scanning Calorimetry (DSC) but the technique used in the present study is simpler and cost-effective. The same technique can also be applied to other liquid crystal samples to study their phase transition behaviour. Keywords: Ferroelectric Liquid Crystal, Optical Rotation, Optical Transmittance, Polarizing Microscope, Phase Transition

Characterization and applications of a newly formulated ferroelectric liquid crystal mixture W315

In this article, we present the formulation, characterization, and application of a newly prepared ferroelectric liquid crystal (FLC) mixture namely W315 composed of pyrimidine compounds. The characterization of FLC material under investigation has been performed through polarizing optical microscopic, dielectric spectroscopic, differential scanning calorimetric and other electro-optical methods. The temperature dependence of the dielectric loss factor of the homogeneously aligned FLC sample shows a phase change from Smectic C* to Smectic A that further confirms the transition temperature of FLC material. From electro-optical observations, the values of spontaneous polarization, rotational viscosity, and response time of W315 were found to be 8.03 nC/cm2, 86.56 mPa s, and 890 µs respectively. The material constants of FLC material under investigation can be utilized in various FLC based faster displays and non-display devices.

Dielectric Studies in Spherical Silica Nanoparticles doped Ferroelectric Liquid Crystal Mixture

in this paper, spherical silica nanoparticles were doped into a ferroelectric liquid crystal (FLC) material. Dielectric studies were carried out in the frequency range of 20Hz-1MHz. Temperature and frequency dependent dielectric permittivity were investigated in the undoped and doped samples. It was observed that adding a small amount of SNPs, the permittivity increases ∼20% than pure FLC mixture. A Goldstone mode was observed in both pristine FLC and SNPs doped FLC samples. The relaxation frequency of detected mode was also observed at ∼570 Hz and ∼715 Hz for pristine FLC and doped samples respectively at 34°C. A single relaxation behaviour was also described in the form of Cole-Cole plot.

Bismuth ferrite nanoparticles for modulation of helical structure at the interface of ferroelectric liquid crystal and substrate

We report the impact of dispersion of bismuth ferrite nanoparticles (BF-NPs) on the helical structure of a ferroelectric liquid crystal (FLC) in two ways: on the surface and into the bulk of FLC. The optical textural observations of the FLC sample cell with BF-NPs on the surface of the substrate show a remarkable change of three different domains having varied molecular orientation in comparison to pure and bulk dispersed FLC, where only two types of domains of different molecular orientations are observed at room temperature. These observations have confirmed distinct molecular dynamics in all the samples. The dispersion of BF-NPs in the bulk of FLC causes a slight shift in a chiral smectic C* (SmC*)–chiral smectic A* (SmA*) phase transition toward a higher temperature. The Goldstone mode (GM) relaxation frequency of the bulk dispersed sample is shifted toward the higher frequency as the temperature is increased and finally is suppressed once the transition from the SmC* phase to the SmA* phase occurs. A relaxation phenomenon is observed other than the GM in the SmC* range and is known as the partially unwound helical mode (p-UHM), contributing to the overall permittivity at lower frequencies. The p-UHM mode is mainly a surface effect that appears due to the fluctuation of partially unwound helix at the surface. The p-UHM process is observed in both cases, i.e., bulk and surface dispersed BF-NPs in the FLC. The influential contribution of the p-UHM has exhibited dielectric properties in its intrinsic frequency range, making the materials suitable for future display devices.

Enhancement of dielectric and electro-optical parameters of a newly prepared ferroelectric liquid crystal mixture by dispersing nano-sized copper oxide

ABSTRACT Here, we present the effect of copper (II) oxide nanoparticles (nCuO) on dielectric and electro-optical parameters of a newly prepared ferroelectric liquid crystal (FLC) mixture, namely W302. The FLC mixture, comprising of pyrimidine compounds, was characterised through dielectric spectroscopy, differential scanning calorimetry (DSC), polarising optical microscopy (POM) and other electro-optical methods. The material parameters such as spontaneous polarisation, rotational viscosity, response time and tilt angle of W302 were found to be 14 nC/cm2, 240 mPa.s, 150 µs and 28ᴼ, respectively. The phase transition temperatures of W302 were observed through DSC and further confirmed by the dependence of dielectric loss factor in homogeneously aligned FLC sample with temperature. We also demonstrate the observance of a low-frequency dielectric relaxation mode due to the unwinding of the helix, called as partially unwound helical mode (p-UHM) along with Goldstone mode. The behaviour of p-UHM has been systematically studied with temperature and applied bias field. Further, dispersion of nCuO into host W302 has shown a significant increase in dielectric permittivity. Also, the p-UHM relaxation peak in the dielectric regime has disappeared with the incorporation of nCuO. These studies would be useful to fabricate better electro-optical devices for display, switching and beam steering applications. The formulation and characterization of a ferroelectric liquid crystal (FLC) mixture W302 composed of pyrimidine compounds is presented. Then, we observed the effect of copper (II) oxide nanoparticles (nCuO) on dielectric and electro-optical parameters of a newly prepared and characterized FLC mixture.

Dielectric response of ferroelectric liquid crystals in samples of finite thickness

The structure in real planar samples of ferroelectric liquid crystals as well as the collective modes characterizing these structures, are strongly affected by surface anchoring of molecules. This is reflected in dielectric properties, which become significantly dependent on the sample thickness. The dielectric strength and the relaxation frequency of the characteristic modes (pinned Goldstone mode for the thick samples and twisted mode for the thin ones) are determined and found that for both types of structures the dielectric strength increases and the relaxation frequency decreases with increasing the sample thickness. We proved theoretically predicted thickness dependences of various physical parameters for new ferroelectric liquid crystalline compound. We concluded the experimental results are in accordance with the theory taking into account the real structure of the samples.

Size-dependent studies in ferromagnetic nanoparticles dispersed ferroelectric liquid crystal mixtures

ABSTRACTIn the present study, ferromagnetic nickel nanoparticles (NiNPs) of size (~20 nm, 40 nm) into ferroelectric liquid crystal (FLC) mixture has been dispersed and investigated. Effect of size of NiNPs on the electro-optic, dielectric and optical properties of FLC mixture have been studied and discussed. A minor improvement in spontaneous polarisation, rotational viscosity and faster response time in NiNPs-FLC samples than pure FLC is noticed. Goldstone mode of relaxation frequency ~100 Hz is detected in all samples and follow a Debye type relaxation behaviour. In addition, it is observed that size of NiNPs does not have any remarkable effect on relaxation frequency and dielectric strength. A single absorption peak at 363, 362 Hz is also noticed in pure FLC and NiNPs-FLC samples.

Dielectric and polarization switching studies in nickel nanoparticles dispersed ferroelectric liquid crystal mixtures

ABSTRACTWe have investigated the effect of nickel nanoparticles (NiNPs) in a pure ferroelectric liquid crystal (FLC) mixture. Dielectric spectroscopy was done in the frequency range of 20 Hz–10 MHz. Switching time, spontaneous polarisation, rotational viscosity has been measured using field reversal technique in SmC* phase. The spontaneous polarisation increases for NiNPs-FLC sample which may be due to the induced dipole moments around FLC molecules. Response time decreases with temperature and NiNPs dispersion. The relaxation frequency and dielectric strength of observed mode in SmC* phase is also discussed in pure FLC and NiNPs-FLC samples. The relaxation frequency in NiNPs-FLC sample decreases than pure FLC sample and found ∼120 Hz.

Dielectric and electro-optical properties of Mn12-acetate and ferroelectric liquid crystal composite

ABSTRACTThe impact of single-molecule magnet (SMM), Mn12-acetate, on the dielectric properties of ferroelectric liquid crystal (FLC) has been investigated by dielectric spectroscopy and electro-optical techniques in a dual electrode sample cell (DESC). The temperature-dependent dielectric studies on Mn12-acetate/FLC composite have revealed the enhancement in the ferroelectric (smectic C*) to paraelectric (smectic A*) phase transition temperature by 3.5°C. The relaxation process corresponding to Goldstone mode in the ferroelectric phase of the composite is found to be slower compared to pure FLC sample. The electrical response for an input triangular wave shows the existence of one extra polarisation peak in Mn12-acetate/FLC composite which is ascribed to the induced dipole moment in Mn12-acetate molecule. The electro-optical texture of Mn12-acetate/FLC composite revealed that the incorporation of SMM in FLC significantly improve the memory effect.

Properties of Ferroelectric Liquid Crystal/Multiwall Carbon Nanotube Doped Composite

Carbon nanotubes-ferroelectric liquid crystal composites have been prepared and studied. Doping of carbon nanotubes into ferroelectric liquid crystal in varying concentration has been investigated in thin cells in the frequency range of 50 Hz–1 MHz. Decrease in the dielectric permittivity and dielectric strength is found with the doping of carbon nanotubes, however ∼32% increase in the relaxation frequency has been observed in higher concentration carbon nanotubes doped ferroelectric liquid crystal composite than pure ferroelectric liquid crystal sample. A decrease in conductivity has also been noticed after doping.

Observation of memory behaviour in cadmium sulphide nanorods doped ferroelectric liquid crystal mixture

In this study, cadmium sulphide (CdS) nanorods doped ferroelectric liquid crystal (FLC) sample cells have been prepared and studied. A memory effect has been observed in CdS nanorods (≤0.3 wt%) doped FLC mixture and confirmed by textures, dielectric and optical studies. The addition of nanorods increases the memory behaviour and efficiency. The occurrence of memory behaviour has been explained due to charge transfer from liquid crystal molecules to CdS nanorods and exists there for 5–15 min in 0.1–0.3 wt% CdS nanorods doped samples. An improvement in polarization, switching time, threshold voltage and rise time parameters has also been noticed in CdS nanorods doped FLC samples.

Electro-optic, thermo-optic and dielectric responses of multiwalled carbon nanotube doped ferroelectric liquid crystal thin films

Multiwalled carbon nanotubes (MWCNTs) doped ferroelectric liquid crystal (FLC) (KCFLC10R) thin films in different (0.00, 0.01 and 0.03 wt./wt.%) ratios have been prepared and studied. In doped sample, fastening of switching time about ~ 80% has been observed. In addition to that, an increase in spontaneous polarization and decrease in rotational viscosity in doped samples than pure FLC sample was also noticed. Improvement in electro-optic responses in doped cells is due to the ion trapping which results an enhancement in effective electric field applied to the liquid crystal cells. Dielectric measurements revealed a decrease in permittivity in doped sample cell as compared to pure FLC cell. Conductivity behavior with MWCNTs concentration has been investigated. MWCNTs doping has good response in terms of increased contrast ratio and low threshold voltage over pure FLC cell.

Anisotropic behavior of water in ferroelectric liquid crystals

The outcome of water addition in ferroelectric liquid crystal (FLC) has been investigated in uniform and defect-free homogeneous and homeotropically aligned monodomain sample cells from electro-optical and dielectric spectroscopic measurements. The lagging in optical response between nonconducting (spatially variable switching) and conducting (conventional switching) portions of water added FLC sample cell has been observed by frequency-dependent electro-optical studies. The bias-dependent water related new relaxation peak near the conventional Goldstone mode relaxation process has been observed only in the homogeneous alignment and not in the homeotropic one. Further, the significant increment in dielectric anisotropy as well as faster diffusion of water along long molecular axis than short molecular axis has also been monitored. These studies strongly suggest that the distribution of water is anisotropic in FLC medium and could be the reason for new relaxation peak in the water added FLC sample.

二向色性偶氮染料对铁电液晶的影响

In order to study the effect of mixing dye in ferroelectric liquid crystal (FLC) materials, the phase transition temperature and electro-optical properties of azo dye doped FLC samples have been investigated. All the properties have been found to be changed drastically. The results have revealed that not only the SmC*-SmA* transition temperature decreased markedly by the addition of azo-dye, but also dye-doped FLC had lower threshold voltage and saturation voltage than the pure FLC.

Effect of Dichroic dye on dielectric properties of ferroelectric liquid crystals: A comparative study

In order to study the effect of mixing dye molecules in ferroelectric liquid crystals, we have investigated two ferroelectric liquid crystal samples CS1016 and Felix 17/000 along with their mixture with Anthraquinone dye. The measurements have been made in the frequency range 100 Hz–10 MHz, with the variation of temperature from 30 to 90 °C. The dielectric behaviour of dye mixed CS1016 is quite different from that of Felix 17/000. This different behaviour has been explained by determining other parameters like distribution parameter, dielectric strength and relaxation frequency, etc. The different nature shown by two different samples has also been explained by electro-optical measurements.

INFLUENCE OF CONFINING GEOMETRY ON THE DIELECTRIC BEHAVIOR OF A FLC SAMPLE HAVING TGBA PHASE

We report on the dielectric permittivities in 1 kHz to 4 MHz frequency region of the ferroelectric liquid crystal (FLC) material CB500 having a TGBA phase. Molecular and collective relaxation processes have been studied in bulk and in confined environment. In the bulk sample, a Goldstone mode (GM) and a molecular mode were observed in the SmC* phase and the softmode (SM) was observed in the TGBA phase. The Goldstone mode was also present in the FLC sample confined in 0.2 μm Anopore membranes. The relaxation frequency of this mode was shifted to the higher-frequency region in comparison to that observed in the bulk sample. In the Anopore confined FLC sample, another relaxation process (AP) was observed, which possibly arises due to some collective movement of the molecules attached to the cavity walls. The relaxation frequency of this process is almost independent of temperature and this process is only observed in the SmC* phase.

Effect of annealing on the dielectric parameters of ferroelectric TSiKN65

The ionic conductivity of ferroelectric liquid crystals used for pyroelectric detection is a measure of the noise contribution to the output of the device. This is obtained from a measurement of the dielectric loss of the liquid crystal material. An annealing procedure has been developed that reduces the ionic conductivity and hence the dielectric loss significantly. The procedure consists of subjecting the ferroelectric liquid crystal sample to an electric field in the isotropic phase and cooling it into the smectic phase at a certain rate. After measurement of the dielectric parameters, the sample is reheated into the isotropic phase and then cooled again at a slower rate into the smectic phase. The dielectric measurements are repeated again. The entire process is repeated for successively slower cooling rates. We present the results of the effect of this annealing treatment on the dielectric parameters and explain the origin of this phenomenon.

Influence of Annealing on the Dielectric Properties of a Ferroelectric Liquid Crystal

The noise level in a pyroelectric device and therefore the sensitivity is dictated mainly by the dielectric losses in pyroelectric materials. An annealing procedure has been developed that reduces the dielectric loss significantly. The procedure consists of subjecting the ferroelectric liquid crystal sample to an electric field in the isotropic phase and cooling it into the smectic phase at a certain rate. After measurement of the dielectric parameters, the sample is reheated into the isotropic phase and then cooled again at a slower rate into the smectic phase. The entire process is repeated for successively slower cooling rates. We present the results of this annealing treatment and explain the origin of this phenomenon.

Experimental indication of macroscopic polarization parallel to the tilt plane in free-standing films of ferroelectric liquid crystals 8SI* and DOBAMBC

Optical reflectivity and x-ray studies have been conducted on free-standing films and bulk samples of ferroelectric liquid crystals near the smectic-A-smectic-C* transition. A tilt plane rotation with respect to the direction of an applied electric field is found in the ferroelectric films above the bulk transition temperature. Whereas the macroscopic polarization is perpendicular to the tilt plane at low temperature, it is parallel to the tilt plane at elevated temperature. The temperature dependence of the average tilt angle is measured.