Ferroelectric Liquid Crystal Matrix 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.

Evidence of cholesterol crystallization along with smectic layers in ferroelectric liquid crystal

We report the crystallization of cholesterol (concentration in ethanol 100, 200, 300, and 400 mg/dl) in combination with ferroelectric liquid crystal (FLC) in the form of cholesterol needles. This has been investigated by dielectric spectroscopy, Raman spectroscopy, and texture analysis through optical micrographs. The foremost impression of adding cholesterol is observed with a reduction in the relative dielectric permittivity value and ferroelectric (chiral smectic C, SmC∗) to paraelectric (chiral smectic A, SmA∗) phase transition temperature with increasing concentration of cholesterol in FLC. In higher concentrations of 300 and 400 mg/dl, crystallized needles have been observed as a result of the supersaturation state of cholesterol in FLC matrix. Texture analysis has revealed that these needles are optically birefringent. Elongation of needles is found to be perpendicular to the FLC molecular director, and hence parallel to the smectic layers also. Temperature dependent investigation has shown that cholesterol-based needles disappear gradually with temperature and has not been observed in nematic and isotropic phases of the material. The results have confirmed that the lines are not only the supersaturation of cholesterol only but it is the composition of both cholesterol and FLC material. This is because when these needles disappear in SmA∗ phase the focal conic domains appear there. The understanding of the behavior of the cholesterol addition on the properties of FLC could be helpful in exploring the possibilities of using FLC as a sensing element in the biosensing of cholesterol and other molecules.

Electro-optic switching and memory effect in suspension of ferroelectric liquid crystal and iron oxide nanoparticles

In this work, impact of dispersion of iron oxide nanoparticles (Fe2O3 NPs) into ferroelectric liquid crystal (FLC) SCE-13 mixture on the electro-optical and dielectric properties has been studied. It has been found that the dispersion of Fe2O3 NPs in host FLC matrix exhibits pronounced influence on response time, spontaneous polarization, rotational viscosity and voltage required for switching the FLC molecules. Also dispersed system shows memory effect as confirmed by the optical texture and dielectric permittivity studies. Effort has been made to explain the experimental results as for as possible.

Alignment of polymer dispersed nanometric films of ferroelectric liquid crystalline molecules

Composite films of polyvinyl alcohol dispersed in ferroelectric liquid crystal (FLC) matrix are fabricated by using Langmuir–Blodgett technique. Pressure–area isotherms show that the composite system formed well aligned monolayer as compared to undoped FLC. Due to molecular interactions, monolayers and multilayers possess good spreading properties and we are able to transfer them onto solid substrates from air-liquid interface. FTIR spectroscopy was used to examine presence of all transferred functional groups on substrate. X-Ray spectrum indicates that even due to presence of PVA in FLC matrix, smectic layer ordering of FLC molecules remains unaltered. During non-contact mode of atomic force microscopy, dense and well aligned homogenous pattern is observed in scanned images.

ZnO/FLC nanocomposites with low driving voltage and non-volatile memory for information storage applications

Nanocomposites comprises of nano sized zinc oxide (ZnO, size ~10 nm) particles and ferroelectric liquid crystal (FLC) material have been prepared and studied. The concentration of the dopant (ZnO nanoparticles) in FLC matrix varied from 0.0 to 1 wt%. Distinct nanocomposites have been used to fabricate memory device and studied through dielectric spectroscopy, optical microscopy and electro-optical methods to explore electro-optic and memory parameters. Experimental results reveal that doping of ZnO nanoparticles in FLC leads to long lasting memory and low deriving voltage in nanocomposites. The achieved prolonged memory effect in nanocomposites may attribute to the charge transfer at the interfaces. Another reason, application of applied field may lead to ion trapping effect at ZnO surface which in turn minimize the depolarized field and enhance the memory effect in nanocomposites.

Influence of SiO2 nanoparticles on the dielectric properties and anchoring energy parameters of pure ferroelectric liquid crystal

In this study, we have investigated the electrical and anchoring energy of ferroelectric liquid crystal (FLC) with the dispersion of SiO2 nanoparticles (NPs). Due to their higher average spontaneous polarization and helical arrangement of FLC molecules, the molecules strongly interacted to SiO2 NPs which increased the value of dielectric permittivity and anchoring energy parameters as demonstrated by the dielectric and electro-optic properties measurement. This two-dimensional array of molecules has been exploited through the study of dielectric permittivity and dielectric loss in presence of silica NPs from low frequency regime to high frequency region in deep smectic phase. In present work we reported dielectric and electro-optical parameters for pristine FLC and SiO2+FLC composites (0.5% and 1.0% wt/wt concentrations of SiO2 NPs). The dielectric permittivity and dielectric loss have been calculated from the measurement of capacitance and conductance with variation of frequency and concentration of NPs as well. The dispersion and polarization anchoring energy coefficients have been calculated from electro-optic properties measurement with the function of applied voltage for pure and SiO2+FLC composites. The dielectric permittivity has increased with the dispersion of SiO2 NPs in pure FLC matrix and relaxation frequency shifted towards high and low frequency region for low (0.5%) and high (1.0%) concentrations of NPs. The spontaneous polarization of SiO2+FLC composites is increased as compared to pure FLC. The experimental results are explained on the basis of different intermolecular interactions arising between FLC molecules and SiO2 NPs.

CuInS2/ZnS QD-ferroelectric liquid crystal mixtures for faster electro-optical devices and their energy storage aspects

CuInS2/ZnS core/shell quantum dots (CIS/ZnS QDs) dispersed ferroelectric liquid crystal (FLC) mixtures have been characterized for their application in electro-optical devices, energy storage, and solar cells. Physical properties of the CIS/ZnS QD-FLC (ferroelectric liquid crystal) mixtures have also been investigated with varying QD concentrations in order to optimize the critical concentration of QDs in mixtures. The presence of QDs breaks the geometrical symmetry in the FLC matrix, which results in a change in the physical properties of the mixtures. We observed the reduced values of primary and secondary order parameters (tilt angle and spontaneous polarization, respectively) for mixtures, which also depend on the concentration of QDs. The reduction of spontaneous polarization in QDs-FLC mixtures is attributed to the adverse role of flexoelectric contribution in the mixtures. The 92% faster electro-optic response and enhanced capacitance indicate the possible application of these mixtures in electro-optical devices and solar cells. Photoluminescence emission of pure FLC and QDs-FLC mixtures has been thermally tailored, which is explained by suitable models.

Pico-ampere current sensitivity and CdSe quantum dots assembly assisted charge transport in ferroelectric liquid crystal

Octadecylamine capped CdSe quantum dots (QDs) dispersed 4-(1-methyl-heptyloxy)-benzoic acid 4′-octyloxy-biphenyl-4-yl ester ferroelectric liquid crystal (FLC) were deposited over gold coated quartz substrate using dip-coating. The topographical investigation discloses that the homogeneously dispersed QDs adopt face-on to edge-on assembly in FLC matrix owing to their concentration. Current–voltage (I–V) measurement was performed using conductive atomic force microscopy (CAFM) which yields ohmic to critical diode like I–V curves depending upon the concentration of QDs in FLC. The recorded pico-ampere (pA) current sensitivity in FLC-QDs composites is attributed to micro-second drift time of electron due to weak electronic coupling between the π-electrons on the FLC and s-electrons on the metal surface. The observed pico-ampere sensitivity is the least current sensitivity recorded so far. For FLC-QDs composites, almost 24% faster electro-optic response was observed in comparison to pure FLC. The pico-ampere current sensitivity can be utilized in touch screen displays whereas the change in polarization for low applied electric field ameliorates the increased electrical susceptibility counteracting the internal electric field and its use in electronic data storage and faster electro-optical devices.

Self assembling effects of nano-particles in mesomorphic LB films

abstractLangmuir–Blodgett (LB) films of ferroelectric liquid crystal (FLC) doped with low concentration of functionalized nano-particles were prepared and characterised. Technique provides uniqueness for controlling molecular architecture through self-assembling. Pressure–area isotherms indicate nano-particles as well as FLC composite systems have capability to from stable monolayer. The molecular interaction between nano-particles and FLC molecules get increased during barrier compression. We observed various phase changes with doping of nano-particles in the FLC matrix. X-Ray diffraction confirmed that FLC retains its SmC* structure at low concentration doping of nano-particles. AFM images indicate that composites are deposited without disturbing translation behaviour FLC.

Mn2+ doped ZnS quantum dots in ferroelectric liquid crystal matrix: Analysis of new relaxation phenomenon, faster optical response, and concentration dependent quenching in photoluminescence

Phase transitional, dielectric, electro-optical, polarizing optical microscopic, photoluminescence (PL), and Fourier transformed infrared (FTIR) spectroscopic measurements have been carried out on ZnS:Mn quantum dots (QDs) dispersed ferroelectric liquid crystal (FLC). A new dielectric relaxation mode has been envisaged in FLC material due to the presence of 0.25 wt. % ZnS:Mn (40 mol. %) QDs. The characteristics of the new mode have been compared with those of the soft mode. A significant fastening of the electro-optical response (∼75%) has been observed in the case of 0.25 wt. % ZnS:Mn (20 mol. %) QDs doped FLC material. The induction of the new relaxation mode is attributed to the flexoelectric tilt fluctuations. The induced flexoelectric polarization in the FLC medium at the vicinity of QDs might be responsible for the enhanced spontaneous polarization in the FLC/QDs mixtures. Quenching in PL for the FLC/QDs mixtures has been observed, which strongly depends on Mn content in QDs. The change in FTIR spectra for the FLC/QDs composite clearly indicates the change in molecular dynamics of the pure FLC after the dispersion of QDs. The presented results will certainly pave a way to utilize QDs for obtaining faster response of the FLC material and potential material to tune the relaxation processes.

Effect of two different size chiral ligand-capped gold nanoparticle dopants on the electro-optic and dielectric dynamics of a ferroelectric liquid crystal mixture

ABSTRACTNanocolloids consisting of a ferroelectric liquid crystal (FLC) doped with different concentrations (0.10 and 0.50 wt.%) of surface treated gold nanoparticles (GNPs) differing in size (1.77, 5.5 nm) are prepared and characterised. The effects of doping on the clearing temperatures as well as electro-optic and dielectric parameters of a FLC mixture are presented. The clearing temperatures remain invariant with doping. A remarkable increase in the spontaneous polarisation is noticed due to the addition of the GNPs with chiral monolayer capping. Tilt angle and switching time, at least in their tendency, become slightly reduced and increased, respectively. Depending on the size of the nanoparticles, surface plasmon resonance is observed to be slightly increased by increasing the surface. In addition, a small change in localised electric field is found upon doping. The increase in the dielectric permittivity and the dielectric strength is observed and attributed to the parallel coupling between the dipoles of functionalised GNPs, induced by external electric field, and the vector of the spontaneous polarisation of the FLC matrix. A decrease in relaxation frequency is observed. A substantial increment of one order in the dc conductivity is also observed for the nanocolloids.

Guest–host interaction in ferroelectric liquid crystal–nanoparticle composite system

The present paper deals with the characterization of a ferroelectric liquid crystal–nanoparticle (FLC–NP) composite system. The dielectric, electrical and polarization property of the FLC–NP composite system have been studied as a function of temperature and frequency. Ferroelectric Cu-doped ZnO (Cu–ZnO) nanoparticles have been added to the pure ferroelectric liquid crystal (FLC) Felix 17/100. The nanoparticles are bigger in size as compared to FLC molecules; therefore, they distort the existing geometry of FLC matrix and set up an antiparallel correlation with the dipole moments of the host FLC molecules. This antiparallel correlation of guest–host geometry reduces the net ferroelectricity of the composite system and modifies all the physical properties of the pure FLC. The change in properties has been analysed and explained in the light of guest–host interaction.

Influence of single-wall carbon nanotubes on Langmuir–Blodgett films of ferroelectric liquid crystals as studied by atomic force microscopy

Langmuir–Blodgett films of ferroelectric liquid crystal (LC) doped with low concentration of single-wall carbon nanotubes have been prepared and characterised. Pressure–area isotherms show that the films are stable and have good spreading properties. The interaction between nanotubes and LC molecules in the monolayer was increased during barrier compression, resulting in increased surface pressure. We observed phase change with increasing nanotube concentration in ferroelectric LC matrix. Atomic force microscopy profiles indicate uniform deposition of material on single crystal silicon wafer.

CdSe quantum dot-dispersed DOBAMBC: an electro-optical study

Cadmium selenide quantum dot (CdSe QD) has been used as a dopant in ferroelectric liquid crystal (FLC) 2-methylbutyl 4-(4-decyloxybenzylideneamino) cinnamate (DOBAMBC). Effect of CdSe QD in DOBAMBC on its different electro-optical (E-O) properties has been studied in the SmC* phase. The optical micrographs recorded for the pure and composite material are showing good dispersion of QDs in the FLC matrix. Micrographs of unaligned sample cell revealed that CdSe QDs induce homeotropic alignment of FLC molecules. An appreciable change in the value of E-O parameters like tilt angle, spontaneous polarisation and response time with shifting of SmA–SmC* phase transition temperature has been observed for CdSe QD–DOBAMBC composite. The observed properties of composite system have been discussed on the basis of surface properties of QDs in FLC system.

Ferroelectric liquid crystal matrix dispersed with Cu doped ZnO nanoparticles

10% Cu doped ZnO nanoparticles (NPs) prepared by hydrothermal and solvothermal method have been dispersed to the pure FLC 17/100 in 1% concentration of guest entity. Electro-optical, elastic and dielectric analysis has been made for the FLC-NPs composite system with the variation of temperature. The nature of the composite system clearly shows the alteration in FLC parameters with the dispersion of NPs. The interaction between crystalline NPs and non-crystalline ferroelectric liquid crystal matrix modifies the properties of the pure FLC system. The synthesis method of NPs is also responsible for the changes taking place in physical properties of the pure FLC. The size and surface defects of the NPs amend the FLC parameters like dielectric permittivity, relaxation frequency, relaxation strength, tilt angle, spontaneous polarization and rotational viscosity etc. The coupling of spontaneous polarization and tilting of the FLC molecules are factors responsible for the resultant electro-optical (E-O) parameters of the composite system.

ZnO1−xSxNanosphere in Ferroelectric Liquid Crystal Matrix: The Effect of Aggregation and Defects on the Dielectric and Electro-Optical Properties

High concentration (5 wt %) ofZnO1−xSxnanosphere (NS) has been dispersed in the ferroelectric liquid crystal (FLC) to analyze the effect of high dopant concentration in the FLC matrix. The FLC molecules actively interact with the NS. The presence of NS enhances the photoluminescence of the pure FLC material due to the coupling of localized surface plasmon resonance from NS with FLC molecules. The high concentration of NS causes an aggregation in the FLC matrix and creates topological defects. The defects and aggregation cause the change in electro-optical and dielectric properties of the pure FLC material. The bigger size of NS as compared to the smectic layer separation causes the warping in the smectic layer. Semiconducting nature of NS also affects the conductivity of the pure FLC.

Changes in material parameters for dye-doped ferroelectric liquid crystal

Addition of the dichroic anthraquinone dye molecules in pure ferroelectric liquid crystal (FLC) matrix results in many improvement in the various vital parameters of the pure FLC. However, addition of anthraquinone dye molecules in pure FLC matrix is not advantageous every time. There are certain constraints which are crucial for the application of these systems into many devices. In this article, we have discussed the concentration and temperature dependence of vital properties of dye-doped FLC. In this study there is improvement in contrast ratio by dye doping due to enhancement in plane switching for dye-doped FLC.

Guest–host mode ferroelectric liquid crystals

The addition of dichroic dye molecules into a pure ferroelectric liquid crystal (FLC) matrix often results in an improvement in the various properties of the pure FLC, particularly optical contrast and viewing angle. During the last few years many authors have studied such systems. However, the addition of a dye to the FLC matrix is not always beneficial, and there are certain constraints which hinder the use of these systems for industrial applications. In the present study the vital properties of a number of dye-doped FLC systems have been investigated. It has been noticed that all their parameters are strongly dependent on the concentration of dye. Improvements are observed up to a certain concentration of dye but above this level the dye is found to have an adverse effect. In this article an attempt is made to explain this unusual behaviour on the basis of the experimental findings.

Curved Ferroelectric Liquid Crystal Matrix Displays Driven by Field-Sequential-Color and Active-Matrix Techniques

This paper describes a curved field-sequential-color matrix display using fast-response ferroelectric liquid crystal. Black matrix and transparent electrode patterns were formed on a thin plastic substrate by a transfer method from a glass substrate. While a composite film of liquid crystal and micro-polymers of walls and fibers was formed between the flexible substrates by printing, laminating and curing processes of a solution of monomers and liquid crystal, the mechanical stability was enhanced by use of multi-functional monomers to form large display panels. The image pixels of the matrix panel were driven by an active matrix scheme using an external switch transistor array at a frequency of 180 Hz for intermittent three-primary-color backlight illumination. The flexible A4-paper-sized color display with 24 × 16 pixels and 60 Hz field frequency was demonstrated by illuminating it with sequential three-primary-color lights from light-emitting diodes of the backlight. Our display system is useful in various information displays because of its freedom of setting and location.

Properties and Stability of Bismuth Doped Tin Oxide Thin Films Deposited on Various Types of Glass Substrates

AbstractThis work reports on deposition of transparent semi-insulating tin oxide thin films deposited by spray-pyrolysis over large area glass substrates. The precursors used are based on diluted chloride solutions. Bi-doped high resistivity tin oxide thin films are required in the fabrication process of an analog grey scale ferroelectric liquid crystal matrix display. Various parameters have been optimized in order to achieve good reproducibility and uniformity of the electrical and optical properties. Deposition temperature and the properties of the glass substrates have been found as the most critical variables which affect the deposition rate and the quality of the deposited films. The different substrates used, borosilicates and soda-lime glasses, lead to different electrical properties. A further investigation on the stability of the film properties versus different kind of aging procedures have been conducted. Preliminary results of the operation of the complete display making use of our films are shown.