Liquid Crystal Mixture Research Articles

Doping white carbon black particles to adjust the electro-opticical properties of PDLC

ABSTRACT Polymer-dispersed liquid crystal (PDLC) is a possible active matrix transparent display technology due to its high transparency, good visibility, and low-power consumption. This paper examined the morphology of polymer-dispersed liquid-crystal materials (PDLCs), which show great potential for display applications. The materials were blends of an eutectic nematic liquid-crystal mixture and a UV-cross-linkable polymeric matrix. White carbon black nanomaterials with high surface adsorbability, high purity, and good stability are ideal materials for the driver circuit of the PDLC display. The influence of the ratio between polymerised monomers and between polymerised monomers and liquid crystals on the electro-optical properties of PDLC system had been studied. We explored the doping of white carbon black nanomaterials in the liquid crystal polymer systems. To achieve this, we have taken advantage of the liquid crystal electro-optical effect experimental instrument to study a series of electro-optical parameters of PDLC, using also additional information on the nanodroplet size and shape distribution provided by SEM images of the PDLC cross-section.

Fabrication and dual-wavelength characterization of a binary mixture of light-responsive polymeric nanocapsules

Two different types of azo dye-doped liquid crystal mixtures were separately nano-confined and characterized and then dispersed in the same host matrix to enhance the wavelength tunability of the laser-induced transparency of the fabricated polymeric thin film nanocomposites. The obtained results indicated that the transmitted intensity can be controlled separately by applying dual-wavelength pump lasers irradiation based-on reorientation of liquid crystal mesogens followed by trans-cis photoisomerization of the different azo dye dopants inside the core of the polymeric nanocapsules. Since the fabricated thin films qualify the demand for improvement of laser-induced tunability, it is feasible to use the introduced nanocomposite as a smart light-responsive thin film layer that can be widely implemented in all-optical tunable nanophotonics.

The effect of the LC mixtures with the different clearing point on temperature dependence of the electro-optical properties of polymer dispersed liquid crystals

Two groups of polymer dispersed liquid crystals (PDLCs) have been studied, results indicated ,when the liquid crystals (LCs) and the UV monomers before curing in the preparation had poor miscibility, the PDLCs showed poor electro-optical properties. Then, we obtained a series of LC mixtures based on E8 and B001, the clearing point of which changed from 71.6 °C to 142.0 °C. The further study on the effect of temperature on the electro-optical properties of PDLCs indicated that PDLCs with high temperature resistance may be obtained by increasing the clearing point of LCs coupled with manipulating other LC parameters.

Dielectric Spectroscopy Analysis of Liquid Crystals Recovered from End-of-Life Liquid Crystal Displays.

In the present work, the dielectric properties of recycled liquid crystals (LCs) (non-purified, purified, and doped with diamond nanoparticles at 0.05, 0.1, and 0.2 wt%) were investigated. The studied LC mixtures were obtained from industrial recycling of end-of-life LC displays presenting mainly nematic phases. Dielectric measurements were carried out at room temperature on a frequency range from 0.1 to 106 Hz using an impedance analyzer. The amplitude of the oscillating voltage was fixed at 1 V using cells with homogeneous and homeotropic alignments. Results show that the dielectric anisotropy of all purified samples presents positive values and decreases after the addition of diamond nanoparticles to the LC mixtures. DC conductivity values were obtained by applying the universal law of dielectric response proposed by Jonscher. In addition, conductivity of the doped LC mixtures is lower than that of the undoped and non-purified LC.

40‐1: Invited Paper: New Liquid Crystal and Reactive Mesogens Mixtures for Passive and Active Photonic Components

We report the current state‐of‐the‐art in liquid crystal and reactive mesogen formulation properties and show how they relate to device performance for both passive and active photonic components for current and future non‐display applications. Development trends and trade‐offs of the formulation properties will be discussed looking into the future.

38‐6: Transparent Display with High‐Contrast‐Ratio Reverse‐Mode PDLC

A chiral liquid crystal containing reverse mode PDLC (Ch‐R‐PDLC), which showed transparent state at 0V, was prepared. This Ch‐R‐PDLC achieved both low voltage driving and strong scattering simultaneously by optimizing the helical pitch length of the chiral liquid crystals and by using original mixtures of liquid crystals and monomers. Transmittance of the Ch‐R‐PDLC was 80% at 0V and 5% at 7V, which was comparable to the normal scattering type. This driving voltage was low enough to employ widely used drivers. A Ch‐R‐PDLC display that was bright in the ON state and highly transparent in the OFF state was also demonstrated.

47‐2: Invited Paper: UBplus — A LC Display Technology Perfect for Energy Saving

“Energy efficiency” and “Green Technology” are currently buzzwords in the display industry. Upcoming mandatory energy regulations are further driving this development, challenging the display industry. Within this context, we would like to demonstrate the advantage of UBplus LC technology for application in TVs. UBplus technology using LC mixtures with negative dielectric anisotropy offers a unique solution to this challenge due to a high transmittance level, whilst retaining the classic FFS cell layout. This paper summarizes the recent developments of liquid crystal mixtures for UBplus.

Optical and thermal studies on binary liquid crystal mixture

The novel binaryliquid crystal mixture is designed and synthesized from 4-methoxycinnamic acid (MCA) and 4-ethoxycinnamic acid
 (ECA). Quantum chemical (DFT) calculation for MCA+ECA geometry is optimized by DFT/B3LYP with 6-311G (d, p) basis set and its
 results are good agreement with experimental data. Fourier-transform infrared spectroscopic(FT-IR) study confirm the presence of
 intermolecular hydrogen bond in the liquid crystal mixture .The paramorphic changes in nematic phase and thermo-optic properties
 of binary liquid crystal mixture isanalyzed using polarizing optical microscope (POM) and differential scanning calorimetry (DSC)
 techniques. A noteworthy observation in the present liquid crystal mixture possesses smectic A phase along with nematic phases.
 Intermolecular hydrogen bond interaction and it’s stabilization energy of present mixture is studied by natural bond orbital (NBO)
 analysis. Due to the transition,the presen tliquid crystal mixtur einduces smecticA phase. The molecular properties of presen t binary liquid crystal mixtureis analyzed by HOMO-LUMO and experimental UV-Visible studies. Thermal spanwidth, stability factor and quantum chemical properties of the liquid crystal mixture are calculated.Molecular electrostatic potential, mulliken atomic
 charge distribution of the optimized MCA+ECA geometry is also reported.

Bioinspired thermal/light-tunable actuators based on predesigned tilted liquid crystal actuators

Smart material-based actuators have attracted much interest because of their envisioned applications in the fields of soft robotics, sensors, and artificial muscles. In this study, we fabricated liquid crystal (LC) actuators via polydopamine (PDA) assistance based on controlling the order parameters. The irregular aggregation of PDA particles coated on the LC film surface was evaluated. To synthesize LC actuators, a predesigned glass sample cell filled with tilt-arranged LCs was fabricated. The LC mixtures were polymerized by 254 nm UV irradiation in glass sample cells. The polymerized LC films showed reversible bending and helical motions depending on predesigned molecular arrangement of the films. This phenomenon was attributed to the phase transition from monodomain to isotropic LC films triggered by temperature and near-infrared light exposure. Adding of chiral dopant shows much higher curling efficiency on thermal stimulation. A hand-shaped actuator with gripping ability was prepared from the synthesized LC networks. The near-infrared light sensitivity of the LC networks was further enhanced using PDA coated on the surface. The observed results suggested that the synthesized LC actuators effectively converted thermal energy and photo-energy to mechanical power. These predesigned LC actuators hold potential for applications as artificial muscles and in micro robotics. A series of thermally tunable liquid crystal elastomeric films was synthesized. Reversible shape variation controlled by temperature or light was achieved based on the order parameter control via the assistance of polydopamine.

Electro-Optical and Photo Stabilization Study of Nematic Ternary Mixture.

Liquid crystal materials composed of mixed nematic compounds find broad use in liquid crystal displays and photonic applications. A ternary mixture formed from three different nematic compounds shows peculiar behavior such as tunable electro-optical properties dependent on the frequency of the driving voltage. The paper presents an analysis of the response time and phase retardation of a frequency tunable nematic liquid crystal mixture (under code name 5005). This material possesses high birefringence (Δn = 0.32 at 633 nm) as well as high dielectric anisotropy (Δε = 6.3 at 100 Hz). The unique property of the 5005 mixture is frequency-controlled phase modulation, as in a dual frequency liquid crystal, while dielectric anisotropy goes to zero instead of being negative at high frequencies. For each component of the mixture, details on mesomorphic properties and their role in the formulation of the mixture are reported. The 5005 mixture was characterized by multiple investigation techniques, such as temperature dependence dielectric anisotropy, transmittance measurements image polarizing microscopy, and UV stability.

Second-order accurate and energy stable numerical scheme for an immiscible binary mixture of nematic liquid crystals and viscous fluids with strong anchoring potentials

We consider in this paper numerical approximations of the immiscible binary mixture of nematic liquid crystals (LCs) and viscous fluids. We develop a second-order time marching scheme by adopting the recently developed stabilized-SAV (scalar auxiliary variable) approach where several critical stabilization terms are added to enhance the stability; thus, large time steps are allowed in computations. The scheme is highly efficient and one only needs to solve several decoupled linear equations with constant coefficients at each time step. The energy stability of the scheme is proved, and various 2D and 3D numerical experiments including the drop deformations and phase separations are then performed to validate the accuracy and energy stability of the proposed scheme.

Studies on electro-optical properties of polymer dispersed liquid crystals doped with reticular nanofiber films prepared by electrospinning

ABSTRACT In this paper, polymer-dispersed liquid crystal (PDLC) films were made from a mixture of prepolymer, liquid crystal and reticular nanofibre films by the polymerisation induced phase separation (PIPS) process. By comparing the microstructure and electro-optical curves of samples with the different liquid crystal content, it was proved that the cavity size of the polymer network has the obvious effect on the electro-optical properties of the PDLC films. Reticular nanofibre films were introduced into samples with different liquid crystal content, and the changes in the polymer network and electro-optical properties of these samples were analysed with SEM images and electro-optical curves. It is established that electro-optical properties and structural peculiarities of PDLC doped with reticular nanofibre films were improved. When the thickness of the embedded nanofibre films continues to increase, the electro-optical properties of the PDLC films can continue to improve. Therefore, the development of reticular nanofibre films doped PDLC films with faster fall time, better contrast ratio will significantly enhance the potential technological applications of PDLC-based devices for smart windows, sensors and flexible devices.

Fabrication of imprinted photonic films via predesigned multiple UV‐polymerizations and their ability to detect solvents and metal ions in aqueous solution

AbstractTo synthesize photonic films without a chiral dopant, a predesigned multiple photopolymerization process was carried out. The photonic films were prepared by the photopolymerization of a mixture of chiral nematic liquid crystals. After polymerization, the chiral dopant, CB15, was removed and recycled. The imprinted photonic polymer films showed Bragg reflection without the presence of the chiral dopant. Upon the sensing of solvents in aqueous solution, significant color changes and peak shifts were observed by the naked eye and ultraviolet–visible spectroscopy, respectively. A linear calibration curve between the central wavelength of the reflection band of the fabricated imprinting film and the volume ratio of 1,4‐dioxane in water was observed. Furthermore, the sensing of chloroform content in methanol, ethanol, and acetone via the imprinted film were also investigated. The results suggest that the synthesized imprinted photonic films can detect different kinds of mixed solvents. The sensing properties of the photonic films were further improved by copolymerization with a rhodamine‐derived monomer. The synthesized modified photonic films can detect heavy metal ions in aqueous solution. This study reports a novel, recyclable, and easy approach to detect organic solvents and copper ions in aqueous solution.

Photoluminescent surface-functionalized graphene quantum dots for spontaneous interfacial homeotropic orientation of liquid crystals

An interfacial molecular array of octadecylamine-functionalized graphene quantum dots (GQDs) was fabricated to simultaneously realize photoluminescence characteristics and molecular orientation for liquid crystals (LCs). The functionalized GQDs were synthesized using a simple bottom-up method by first grafting them with octadecylamine. The subsequent interfacial self-assembly of these functionalized GQDs in an LC medium formed a nanostructured molecular array on an indium tin oxide (ITO) electrode. Experiments revealed that the hydrophobic GQDs spontaneously covered the hydrophilic ITO surface through polar intermolecular interactions, and the resulting GQD layer induced the uniform vertical orientation of the LC molecules at the ITO interface owing to van der Waals interactions of long side chains. In addition, the unique photoluminescence of pure GQDs in the blue region was maintained even in an LC mixture with a low concentration of functionalized GQDs. A new type of homeotropically oriented LC device based on the nanostructured layer of functionalized GQDs exhibited superior electro-optical properties and a 375% improvement in response time for turn-off switching of the device relative to those of a conventional polymer layer. This functionalized GQD-based device simultaneously achieved the spontaneous alignment of the LCs, blue photoluminescence emission, and high-speed response performance for turn-off switching of the device. In addition, our method is cost-effective and encompasses a simple fabrication process for developing functional controllable surfaces without requiring a tedious multi-step manufacturing process.

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.

Magnetic Liquid Switching Using Rodlike Ferronematic 6CHBT Liquid Crystal Mixture Depending on the Diffraction Patterns

Diffraction patterns formed by a ferronematic sample, which contains 4-(trans-4-n-hexylcyclohexyl)-isothiocyanatobenzene (6CHBT) liquid crystal doped with Fe3O4 rodlike magnetic nanoparticles, was studied. The studied mixture can be applicated as a liquid magnetic switch. The diffraction patterns were observed from the micro-lines scribed on the polymer layer, which was contained by the liquid crystal mixture cell, with dimensions of 4 nm for depth and 0.32 µm for width and 5000 line per 1 mm2 in the case of absence and presence of the DC magnetic field. From the experimental results, it was observed that the application of the magnetic field caused more than 17% expansion in the diffraction patterns area at the focused point, while the number of patterns was increased by 25%. This change in the diffraction area due to the application of a magnetic field gives the motive to sense the low DC magnetic field which could be useful in the application of liquid switching.

Design and Realization of a Compact Efficient Beam Combiner, Based on Liquid Crystal Pancharatnam–Berry Phase Gratings

We demonstrate a laser beam combiner based on four photo-patterned Pancharatnam–Berry (PB) phase gratings, which is compact and has high diffraction efficiency for incident circularly polarized light. The nematic liquid crystal mixture E7 is used as anisotropic material, and the thickness of the layer is controlled by spacers. The beam combiner can bring two parallel laser beams closer to each other while remaining parallel. This work shows the potential to realize components based on flat optical LC devices.

Effect of γ-irradiation on various important physical properties of a room temperature ferroelectric liquid crystal mixture and its silver nanocomposite

A room temperature ferroelectric liquid crystal (FLC) mixture and its silver nanocomposite have been irradiated by various doses of γ-radiation from 60Co. Phase transition temperatures, dielectric permittivity, optical tilt angle, spontaneous polarization, rotational viscosity, switching time, and conductivity of the systems have been determined as a function of the irradiation dose and temperature. Phase transition temperatures and optical tilt angles of both the systems decrease significantly, more in the pristine mixture, meaning a decrease of the order parameter with irradiation. Remarkable changes are exhibited in the dielectric permittivity as well as in their molecular dynamics as confirmed by the change in Goldstone and soft mode relaxation frequencies. The conductivity of the irradiated mixture increases considerably compared to its nanocomposite probably due to the production of more ions by the radiolysis process. Spontaneous polarization, rotational viscosity, and switching time are also found to decrease linearly with irradiation dose. At the maximum absorbed dose, switching time decreases by 140 μs in the pristine mixture and 110 μs in the nanocomposite suggesting their more suitability in display applications. The concentration of the chiral dopant also influences the impact of irradiation.

Pearl-inspired polymer films with chiral nematic and multi-lamellar structures

ABSTRACT Structural coloured materials have been widely found in nature. More and more artificial materials were created based on structural colour. However, fabrication of polymer films with pearly lustre remains a challenging task. Herein, a strategy is reported to prepare broadband reflection polymer films based on the fluorophilic association. A monomer with a perfluorooctyl chain is synthesised. After photo-crosslinking a mixture of a chiral nematic liquid crystal and the fluorinated monomer, broadband reflection film with pearly lustre is obtained. The broadband reflection originates from the broad distribution of the helical pitch. The pearly lustre is caused by the periodically ordered layers formed by the microphase separation between hydrocarbon and fluorocarbon chains.A strategy for the preparation of color liquid crystal polymer film with pearly luster is developed. The Bragg-reflection color originates from the supramolecular helical structure of the cholesteric liquid crystal and the pearly luster originates from the multilayer structure formed by the fluorocarbon/hydrocarbon microphase separation

5.3: Invited Paper: High Efficiency Phase Modulators

In communication networks, wavelength selective switch (WSS) is one of the key components in reconfigurable optical add‐drop multiplexer (ROADM) [1]. Several technologies have been developed to achieve a high‐performance WSS, such as micro electromechanical systems (MEMS) [2], liquid crystal on silicon (LCOS) [3], arrayed waveguide grating (AWG) [4], and hybrid planar lightwave circuit (PLC)‐MEMS [5]. Among these, LCOS‐based WSS is most attractive for the next‐generation optical networks due to its controllability with individual electrical control on pixel. It shows advantages of flexible bandwidth adjustment, adaptive alignment, and robustness without mechanical movements.A LCOS exhibiting a high diffraction efficiency at a large deflection angle is demonstrated [6]. A liquid crystal (LC) mixture with a large birefringence (Δn = 0.27, at λ = 1550 nm) and a large dielectric constant (Δε = 10.4) is developed to obtain the high‐phase retardation, more than 4π, at 1550 nm within a relatively low operation voltage of 5.5 V on LCOS. When compared with the conventional modulation method of 2π phase retardation, both grating period and phase retardation are doubled in 4π modulo modulation. Using the high‐phase retardation modulation method, the LCOS may achieve high diffraction efficiency, more than 56.6% at 4.5° deflection angle of C‐band wavelength with an optimized phase retardation profile.A polarization‐independent blue phase liquid crystal on silicon (BPLCoS) device with low operation voltage for 2π phase depth is proposed [7]. With optimized reflection structure and two reflection films, the incident light may experience multifold optical path and 2π phase depth can be obtained. For the polarization‐independence, an inclined electric field made by periodical gradient voltage is applied on the blue phase liquid crystal (BPLC) to match the light propagation direction. With the structure, the operation voltage can be lowered to 5.5 V in simulation and 5.9 V in experiment for 2π phase modulation at 1550 nm.The high diffraction efficiency and polarization‐independent phase modulators show the great potential application of beam steering for the optical communication and the holographic display.