Ferroelectric Liquid Crystal Mixture Research Articles

Dielectric and electro-optical studies of a nickel-ferrite-nanoparticle- doped ferroelectric liquid crystal mixture

Effect of magnetic nanoparticles (nickel ferrite) doping on the dielectric and electro-optical properties of a ferroelectric liquid crystal mixture has been studied. In a doped ferroelectric liquid crystal mixture, dispersion of a small amount (0.25 wt.%) of nickel ferrite nanoparticles decreases the polarization and improves the response time compared to an undoped mixture. The significant changes in the polarization and response time are explained on the basis of dipole–dipole interaction and anchoring phenomena. Dielectric permittivity also increases with increasing the temperature of the SmC* phase and shows a reduction in dielectric loss in a doped sample. A Goldstone mode is clearly observed at ∼200 and ∼500 Hz in an undoped and a doped sample, respectively.

Binary Mixtures of Hydrogen-Bonded Ferroelectric Liquid Crystals: Thermal Span Enhancement in Smectic X* Phase

Abstract Thermotropic hydrogen-bonded ferroelectric binary liquid crystal mixtures comprising of N-carbamyl-l-glutamic acid (CGA) and p-n-alkyloxy benzoic acids (BAO) are investigated. Variation in the molar proportion of X and Y (where X=CGA+5BAO and Y=CGA+9BAO, CGA+10BAO, CGA+11BAO, and CGA+12BAO) comprising of four series yielded 36 binary mixtures. Optical and thermal properties of these mixtures are meticulously studied in the present article. In addition to the traditional phases, a novel smectic ordering namely smectic X* is observed in all the four series. The aim of the investigation is to obtain abundance occurrence of smectic X* with a large thermal span, and hence, the proportions of the binary mixtures are so chosen that the prelude task is accomplished. Optical tilt angle in smectic X* and smectic C* phases is experimentally determined, and a theoretical fit is performed. Phase diagrams of the four series are constructed from the data obtained from the differential scanning calorimetry and correlated with the phases recorded by the polarising optical microscope studies. Thermal stability factor and thermal equilibrium are also premeditated.

36.4:Invited Paper: Real‐Time Light Amplification by Photorefractive Ferroelectric Liquid Crystal Mixtures

The photorefractive effect in photoconductive ferroelectric liquid crystals that contain photoconductive chiral compounds was investigated. Ter‐thiophene compounds with chiral structures were chosen as the photoconductive chiral compounds, and they were mixed with an achiral smectic C liquid crystal. The mixtures exhibit the ferroelectric chiral smectic C phase. The photorefractivity of the mixtures was investigated by two‐beam coupling experiments. It was found that the ferroelectric liquid crystals containing the photoconductive chiral compound exhibit a large gain coefficient of over 1200 cm‐1and a fast response time of 1 ms. Real‐time dynamic amplification of an optical image signal of over 30 fps using the photorefractive ferroelectric liquid crystal was demonstrated.

Dielectric behavior of carbon-nanotube-doped ferroelectric liquid crystal mixture

The dielectric spectra of pure and 0.1% multi-walled-carbon-nanotube-(MWCNT)-doped ferroelectric liquid crystal (FLC) mixture KCFLC10S materials were studied in the 50 Hz to 1 MHz frequency range at different bias voltages. An unusual behavior-increase of ϵ′ with increasing E was observed in both samples. It was found that although the relaxation mode was not observable in the MWCNT-FLC sample, the increased effect of the bias voltage on the FLC with the addition of MWCNTs is clearly visible. A theory is presented to explain this effect of MWCNTs in the FLC material.

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.

Influence of ZnO nanoparticle concentration on electro-optic and dielectric properties of ferroelectric liquid crystal mixture

We present here the electro-optic and dielectric properties of ZnO nanoparticle doped ferroelectric liquid crystal (FLC) mixtures. A small quantity of ZnO nanoparticles (0.0, 0.1, 0.3, 0.5 and 1.0wt.%) was dispersed into FLC with a thickness of 5.0±0.2μm. The enhancement in physical parameters is found to be dependent on ZnO nanoparticle concentration. The lower concentration of ZnO nanoparticles (0.1–0.3wt.%) enhances the value of spontaneous polarization and decreases for higher concentration (0.5–1.0wt.%). The fastening of response time has also been noticed in the doped sample cells up to 0.3wt.% concentration. Dielectric measurements revealed a concentration dependence effect in all sample cells. A low threshold voltage and improved contrast ratio has been noticed for 0.3wt.% concentration over other doped samples.

ELECTRO-OPTICAL STUDIES IN A FERROELECTRIC LIQUID CRYSTAL MIXTURE

Symmetric square and triangular wave pulses have been applied across planar cells of different thickness to a ferroelectric liquid crystal mixture in the SmC* phase. Dynamic processes of molecular reorientation associated with the helix unwinding and winding by applying bias (-10V -0V - +10V) and taking micrographs simultaneously have been studied. The spontaneous polarization (PS), response time (τR) and torsional viscosity (η) have been studied as a function of temperature, sample thickness and bias voltage. PS follows the relation PS = Po(Tc - T)β. η obeys the Arrhenius relation from 35°C to 60°C with an activation energy of 0.89 eV for 5.0 μm sample thickness. The surface switching in the thin cell is more dominant due to the strong surface pinning effect.

Suppression of relaxation modes in dye dispersed SmC* phase

We report the results of dielectric and electro-optical properties of ferroelectric liquid crystal (FLC), Felix 17/100, exhibiting chiral smectic C phase and dye dispersed FLCs. The polarization measurement on pristine and dye dispersed FLC mixture shows decrease in the value of polarization, indicating the distribution of dye dipole in a direction opposite to the orientation of FLC molecule. The rotational viscosity also decreases accordingly as shown by the measurement of response time. Dielectric measurement shows existence of two relaxation modes both in pure FLC and dye dispersed FLC. The relaxation strength of Goldstone mode decreases with the dispersion of dye and the relaxation frequency of this mode shifts towards the high-frequency side. The second relaxation mode arises due to the formation of domains at the surface interface. The dispersion of dye into FLC suppresses the domains.

Time evolution photoluminescence studies of quantum dot doped ferroelectric liquid crystals

Time evolution photoluminescence (PL) studies of ferroelectric liquid crystal (FLC) mixtures doped with different concentrations of ZnS and CdS quantum dots (QDs) are carried out. Remarkable enhancement in the PL intensity and a significant shift in the emission band of FLC materials are observed by doping with a suitable amount of QDs. The modifications in the PL behaviour of the QD/FLC composites are found to depend strongly on time, and also on the QD/FLC mixtures themselves. The enhancement in the PL intensity of the FLC materials is attributed to the additive combination of the emissions from FLCs and QDs and the highly scattering phase of the FLC materials used. The shifting of the emission band and reduction in the PL intensity of the QD/FLC composites could be attributed to the oxidation of QDs. The observed results would be helpful in selecting QD/FLC composites to observe stable and enhanced PL from composites.

Size dependence of harvested BaTiO3 nanoparticles on the electro-optic and dielectric properties of ferroelectric liquid crystal nanocolloids

The influence of the size of harvested barium titanate nanoparticles on the properties of ferroelectric liquid crystal (FLC) nanocolloids was investigated by electro-optical and dielectric methods. The spontaneous polarization and the switching time are decreased for the liquid crystalline nanocolloids compared to nondoped FLC mixtures of different dipole strengths; this dependence is stronger for small size particles (9 nm) and weaker for larger size particles (26 nm) by the same concentration in weight. The decrease of the Goldstone mode (GM) relaxation frequency and the decrease of the dielectric GM absorption strength of the nanocomposites compared to the nondoped FLC mixture go stepwise with the increase of the nanoparticles diameter. Results have been interpreted via strong interaction between the FLC dipoles and the dipoles of the highly polar barium titanate nanoparticles.

Influence of Electric Field on the Orientation of Ferroelectric Liquid Crystals inside micro capillaries

In the paper we present recent results on investigation of ferroelectric liquid crystals molecules orientation inside photonic crystal fibers, which consist of a set of micro capillaries. We have infiltrated glass micro capillaries with different inner diameters with the experimental ferroelectric liquid crystal mixture W-206K. The orientation of the liquid crystal molecules was controlled by the external electric field applied to the sample. We have obtained promising results about the orientation of the ferroelectric liquid crystal molecules and their behavior under influence of applied external electric field. The presented results may lead to design a new class of fast-switching fiber optic sensors. Full Text: PDF References P. St.J. Russell, "Photonic-Crystal Fibers", J. Lightwave Technol. 24, 4729-4749 (2006). CrossRef T. Larsen, A. Bjarklev, D. Hermann, and J. Broeng, "Optical devices based on liquid crystal photonic bandgap fibres", Opt. Express 11, 2589-2596 (2003). CrossRef T. R. Wolinski, K. Szaniawska, K. Bondarczuk, P. Lesiak, A.W. Domanski, R. Dabrowski, E. Nowinowski-Kruszelnicki, J. Wojcik, "Propagation properties of photonic crystal fibers filled with nematic liquid crystals", Opto-Electronics Rev. 13(2), 177-182 (2005). DirectLink M.W. Haakestad, et al., "Electrically tunable photonic bandgap guidance in a liquid-crystal-filled photonic crystal fiber", IEEE Photon. Technol. Lett. 17, 819–821 (2005). CrossRef Matuszczyk M. "Structures and Properties of Ferroelectric Liquid Crystal Displays", Goteborg, Sweden, Chalmers Reproservice (1996). Q. Guo, E. P. Pozhidaev, A. K. Srivastava, Y. Ma, X. Wang, V. G. Chigrinov, H. S. Kwok, "Deformed Helix Ferroelectric Display with Low Driving Voltage and Fast Response Time", SID Symposium Digest of Technical Papers, Vol. 43 (1), 449-451, (2012). CrossRef E. P. Pozhidaev et al., "High Frequency Low Voltage Shock-Free Ferroelectric Liquid Crystal: A New Electro-Optical Mode with Electrically Suppressed Helix", Proc. of 31-th International Display Research Conference EuroDisplay 2011, Bordeaux-Arcachon, France, September 19-22 (2011). DirectLink Vladimir Chigrinov, Eugene Pozhidaev, Abhishek Srivastava, Guo Qi, Ma Ying, Hoi Sing Kwok, "Fast Ferroelectric Liquid Crystal Modes Based on Photoaligning Technology", SID 2013, Vancouver, Canada, May 2013 Clark, N. A. and S. T. Lagerwall, "Submicrosecond bistable electro-optic switching in liquid crystals", Appl. Phys. Lett. Vol. 36, 899-901(1980). CrossRef S. Mathews, Y. Semenova, G. Rajan, G. Farrell, "Tunable properties of Liquid Crystal filled Photonic Crystal Fibers", Proc. SPIE 7316, 73161E (2009). CrossRef D. Budaszewski, T.R. Woliński, M. A. Geday, J. M. Otón, "Photonic Crystal Fibers infiltrated with Ferroelectric Liquid Crystals", Phot. Lett. Poland 2(3) (2010). CrossRef

Modification of the electrical parameters of CNT-doped deformed-helix ferro-electric liquid crystals

Liquid crystals are useful for a wide range of applications due to their exceptional properties. Doping of liquid crystals with carbon nanotubes (CNTs), even at very low concentrations, produces a detectable effect on the liquid crystal (LC) properties that can be very attractive for various functions. In this study, an attempt was made to investigate the effect of CNTs on the electrical properties of a short-pitch and high-spontaneous-polarization ferro-electric LC mixture, FLC-6304, at different temperatures. The inclusion of the CNTs significantly reduced the polarization at temperatures well within the SmC* phase, but the effect was gradually reversed as the transition temperature was approached. The insertion of the CNTs also reduced the response time and the rotational viscosity of the FLC mixture, which is highly desirable in the LCD industry.

Nickel nanoparticles doped ferroelectric liquid crystal composites

With the advance of nanoparticles-liquid crystal composites, it became increasingly interesting to measure the various physical parameters, preferably near the transition temperature. In this research work, fine nickel nanoparticles with 2–8nm size distribution were synthesized by chemical reduction of nickel hydrazine complex in aqueous solution at 60°C. A small concentration of 0.5wt.% of nickel nanoparticles dispersed in a novel ferroelectric liquid crystal mixture showed improved transmittance and fast switching response. Moreover, nickel addition indicates a slight increase in the conductivity of the ferroelectric sample. These studies indicate the occurrence of strong dipole interactions between metallic nanoparticles and ferroelectric liquid crystal molecules in the presence of applied electric field.

Dielectric investigations of pure and carbon nanotube-doped deformed helix ferroelectric liquid crystals

The doping of carbon nanotubes (CNTs) into liquid crystals enhances their parameters for use in various applications. Here, an attempt is made to study the effect of CNTs on the dielectric properties of the deformed helix ferroelectric liquid crystals mixture FLC-6304, in different liquid crystal phases. The inclusion of CNTs significantly affect the dielectric parameters in the chiral smectic C phase with an inversion of the effect near the transition to, and in, the chiral smectic A phase

Changes in the electro-optical behaviour of ferroelectric liquid crystal mixture via silica nanoparticles doping

We investigated the dynamic properties of a ferroelectric liquid crystal mixture doped with silica nanoparticles using polarization current reversal method. The effect of temperature and bias field on the switching responses of silica–ferroelectric liquid crystal composites with different silica concentrations (0.01, 0.02, 0.05 and 0.1wt%) were studied and compared. Various electro-optic properties of ferroelectric liquid crystal mixture changed according to silica nanoparticles concentration. We observed about 14% decrease in spontaneous polarization and up to 17% increase in switching response for 0.01wt% silica dispersion, whereas a minor increase in the isotropic temperature of composites. The rotational viscosity and optical contrast increased with increasing silica concentration. At a 0.1wt% silica nanoparticle doping concentration, the ferroelectric liquid crystal cell showed the best electro-optic properties, such as low threshold and driving voltage, better optical contrast and low tilt angle. Our experimental results show that silica doped ferroelectric liquid crystal composites are promising materials for better optical contrast in electro-optical applications.

Ferroelectric Liquid Crystal Mixture Integrated Into Optical Waveguides

We report an on-chip integrated ferroelectric liquid crystal (FLC) waveguide structure suitable for telecommunication applications. Single gaps with different widths of 5, 10, and 20 μ m inside individual silica waveguides were filled with an FLC mixture. The waveguide devices operate as a binary switch or an attenuator in a temperature range from 30 ° C to 60 ° C. The FLC mixture exhibited a good alignment quality in these gaps without alignment layers. A good extinction ratio of up to 33.9 dB and a low insertion loss of <; 4.3 dB at λ = 1550 nm were observed. Switching times of <; 100 μs were obtained for the low electric fields applied in this experiment.

Temperature Dependence of the Tilt Angle for the Smectic A-Smectic Transition in a Mixture of C7-70PDOB Ferroelectric Liquid Crystals near the Tricritical Point

The temperature dependence of the tilt angle is studied in the smectic phase near the smectic A-smectic tricritical point for a mixture of 70PD0B in the ferroelectric liquid crystal C7 (). The mean-field models with the biquadratic ( is the spontaneous polarization) and (bilinear) coupling terms in the free energy expansion are used to analyze the experimental data for the tilt angle in this binary mixture. From our analysis, the coefficients given in the free energy expansion of the mean-field models are determined. Our results show that the mean-field theory explains adequately the observed behaviour of the C7-70PD0B mixture near the tricritical point.

Analysis of Dielectric and Electro-optic Responses of Nanomaterials Doped Ferroelectric Liquid Crystal Mixture

Dielectric and rotational viscosity measurements of a multi-component ferroelectric liquid crystal mixture were performed by adding a small concentration (0.01 wt%) of silica and multi walled carbon nanotubes (MWCNTs). Liquid crystals turn out to be outstanding hosts for nanomaterials. A remarkable increase in the rotational viscosity was noticed in CNT doped system as compared to silica doped same liquid crystal system. Comparison of dielectric studies shows higher value of permittivity and dielectric losses for silica-doped sample than those of CNT doped sample. The results have been interpreted both experimentally and theoretically.

Sign reversal of dielectric anisotropy of ferroelectric liquid crystals doped with cadmium telluride quantum dots

A small amount of cadmium telluride quantum dots (CdTe QDs) has been doped into various ferroelectric liquid crystals (FLCs) to observe the modifications in the alignment and dielectric anisotropy (Δɛ) of the composites. The CdTe QDs have induced a uniform homeotropic (HMT) alignment in most of the FLC mixtures. We observed an unexpected switching (from HMT to homogeneous configuration) of CdTe QDs doped FLC CS1026 (having positive Δɛ) by the application of high dc bias. This reverse switching has been attributed to the interaction between FLC molecules and CdTe QDs which caused the sign reversal of Δɛ of FLC CS1026.

Multiferroic Behaviour in Mixtures of the Ferroelectric Liquid Crystal and Magnetic Nanoparticles

A dielectric spectroscopy, magnetic susceptibility and high resolution calorimetry have been carried out in the vicinity of the ferroelectric smectic C* phase of SCE9 ferroelectric liquid crystal (LC) mixtures with magnetic nanoparticles (NPs) to determine the impact of the magnetic nanoparticles on the Goldstone and soft mode and to study the disordering effects on the ferroelectric phase transition. It was verified via SQUID susceptometer that the indirect coupling between the NPs magnetic moments and the LC electrical polarization exists in these mixtures.