Nematic Liquid Crystal Mixture Research Articles

A high birefringence liquid crystal for lenses with large aperture

This work presents the application of an experimental nematic liquid crystal (LC) mixture (1929) in a large aperture lens. The LC material is composed of terphenyl and biphenyl derivatives compounds with an isothiocyanate terminal group and fluorinated lateral substituents. The substitution with a strongly polar isothiocyanate group and an aromatic rigid core provides pi-electron coupling, providing high birefringence (Delta n = 0.3375 at 636 nm and 23 °C) and low viscosity (eta = 17.03 mPa s). In addition, it also shows high values of birefringence at near infrared (0.318 at 1550 nm). The synthesis process is simple when comparing materials with high melting temperatures. The excellent properties of this LC mixture are demonstrated in a large aperture LC-tunable lens based on a transmission electrode structure. Thanks to the particular characteristics of this mixture, the optical power is high. The high birefringence makes this LC of specific interest for lenses and optical phase modulators and devices, both in the visible and infrared regions.

Eutectic Mixtures of Metallomesogens as Potential Materials for Electro-Optical Applications

In this work, we present a new approach for utilization of eutectic mixtures of metallomesogens (MOM) as potential materials in electro optical devices. We studied the phase diagrams of blends of synthesized rod-like Palladium (Pd) alkyl/alkoxy-azobenzene complexes with their parent ligands and commercial nematic liquid crystal mixtures. The results indicate complete mesgenic miscibility and eutectic points of MOM-ligand mixtures. In addition, the MOMligand eutectic mixture also exhibited a complete nematic miscibility with three commercial liquid crystals TN10427, TNO623 and E43 that qualify them model materials in the guest-host electro-optical devices.

A second-order time accurate and fully-decoupled numerical scheme of the Darcy-Newtonian-Nematic model for two-phase complex fluids confined in the Hele-Shaw cell

We consider the numerical approximation of the binary immiscible mixture of nematic liquid crystals and viscous Newtonian fluids confined in a Hele-Shaw cell, where the free interface motion is simulated by using the phase-field approach via the energy variational method. The governing system is highly complicated nonlinear and coupled, consisting of the Darcy equations for the flow field, the Cahn-Hilliard equations for the free moving interface, and the constitutive equation for the nematic liquid crystal. The numerical scheme developed in this paper is the first “ideal” scheme, namely, it not only has the following characteristics: linearity, second-order time accuracy, unconditional energy stability, and decoupling structure, but also at each time step, only needs to solve a few elliptic equations with constant coefficients. We strictly prove that the scheme satisfies the unconditional energy stability and give a detailed implementation process. Various numerical experiments are further carried out to prove the effectiveness of the scheme, in which the influence of the initial orientations and anchoring elastic energy of the liquid crystal on the Saffman-Taylor fingering instability are studied.

Mesomorphic, electro-optic and dielectric behavior of self-assembled nanocomposite materials: Nematic mixture doped with carbon coated cobalt nanoparticles

In the present study, different concentrations of carbon coated cobalt nanoparticles (0.25 wt% & 0.5 wt%) into eutectic nematic liquid crystal mixture (E7) have been dispersed and studied their mesomorphic, electro-optic and dielectric properties in planar as well as homeotropic aligned cells. Optical transmission method has been employed in planar aligned cell to study the electro-optic responses while dielectric spectroscopy in the frequency span 20 Hz-10 MHz has been performed in planar and homeotropic cells. Nearly 10°C increase in nematic-isotropic transition temperature is noticed at higher doping concentration. Dispersion of cobalt nanoparticles induces changes in dielectric permittivity, dielectric loss and relaxation frequency. Suppression of free ion concentration (in case of 0.5 wt% Co) suggests large dielectric anisotropy values. Entropy of the system is more or less affected with the nano inclusions but the free energy of the doped samples has been decreased. An improvement in threshold voltage, birefringence and order parameter by ∼ 10%, 15% & 5% respectively have been observed at low doping concentration. However, contrast ratio is reduced with the doping of cobalt nanoparticles. The present study shows that the doped systems have improved response than pure E7 and find potential applications in phase shifters as well as display devices.

Optical, dielectric and elastic studies of high birefringent ambient temperature nematic liquid crystal mixtures having similar molecular cores

We report various physical properties such as optical, dielectric, and elastic studies of two high birefringent climate temperature nematic liquid crystal mixtures having similar molecular cores such as quarter phenyl and phenyethnyltolane cores. In both the mixtures, one compound is common, and, in another compound, the lateral group ethyl group is replaced with a methyl group. These mixtures exhibit high birefringence and high elastic constants in comparison to regular liquid crystals. Both the compounds exhibit high birefringence, positive dielectric anisotropy whereas the parallel component shows anomalous temperature dependence. Our results show that with a variation of lateral group, correlation among the cores varies and that reflects in optical and dielectric anisotropies. These studies will be useful in synthesis and exploring appropriate liquid crystals for various display and smart window applications.

On the Miscibility of Nematic Liquid Crystals with Ionic Liquids and Joint Reaction for High Helical Twisting Power Product(s).

Mixtures of nematic liquid crystals (LCs) with chiral ionic liquids (CILs) may find application as active materials for electrically driven broadband mirrors. Five nematic liquid crystal hosts were mixed with twenty three ionic liquids, including chiral ones, and studied in terms of their miscibility within the nematic phase. Phase diagrams of the mixtures with CILs which exhibited twisted nematic phase were determined. Miscibility, at levels between 2 and 5 wt%, was found in six mixtures with cyanobiphenyl-based liquid crystal host—E7. On the other hand, the highest changes in the isotropization temperature was found in the mixtures with isothiocyanate-based liquid crystal host—1825. Occurrence of chemical reactions was found. A novel chiral binaphtyl-based organic salt [N11116][BNDP] was synthesized and, in reaction to the 1825 host, resulted in high helical twisting power product(s). Selectivity of the reaction with the isothiocyanate-based liquid crystal was found.

Probing the impact of bismuth-titanate based nanocomposite on the dielectric and electro-optical features of a nematic liquid crystal material

We report here the concentration and temperature dependent optical, electro-optical and dielectric studies on bismuth titanate (Bi2Ti2O7/Bi4Ti3O12) nanocomposite (BT2/BT4 NC, ∼42 nm) doped nematic liquid crystal (NLC, 5CB) mixtures using optical polarising microscope and dielectric spectroscopic techniques. The optical textures confirm the uniform dispersion and miscibility of NCs in 5CB for all concentrations (i.e. 0.1, 0.25, 0.5, 1 and 2 wt%) and mixtures appear to be almost agglomeration free. The dielectric studies demonstrate the maximum changes in the dielectric parameters (dielectric permittivity, dielectric loss, loss factor and dielectric anisotropy) of 5CB sample for the 0.1 wt% mixture. Interestingly, the dielectric anisotropy of 5CB in 0.1 wt% mixture is increased by ∼ 11%. However, the dielectric memory effect (bias voltage ON-OFF) is observed maximum in the case of 1 wt% mixture. Similarly, the optical memory examined by bias voltage dependent (ON-OFF) optical textures is also significantly enhanced for 1 wt% mixture. The significant changes observed in dielectric properties of 5CB sample could be due to plausible interaction among NLC molecules and ionic impurities with BT2/BT4 NCs. Moreover, the enhanced volatile memory in BT2/BT4 NC-NLC mixture could be attributed to the dipole–dipole coupling between individual permanent dipole moment of anisotropic NLC molecules with the dipole moments generated by the ionic impurities agglomerated on the surface of high dielectric BT2/BT4 NCs. We strongly believe that such NCs-NLC mixtures would be certainly useful in the advancement of wearable devices (such as smart plenoptic cameras, watches etc.) and smart switchable windows.

Effect of size and concentration of magnetic nanoparticles on blue phase stabilization and electro-optical properties in blue phase liquid crystalline nanocomposites

Blue phase liquid crystal material having a wide blue phase range of 7 °C was prepared in a binary mixture of nematic and chiral nematic liquid crystals with optimization of chiral dopant concentration. Magnetic nanoparticles of size 20 nm, 40 nm in varying concentrations (<0.5 wt %) could successfully stabilize the blue phase temperature range. Interestingly, the BP stability increases approximately 7.8 °C with an increase in nanoparticles concentration up to a critical concentration (0.1 wt %) and then gradually decreases at higher concentrations of nickel nanoparticles. A detailed comparative electro-optical study of pure blue phase liquid crystal and size dependent nickel nanoparticles doped blue phase liquid crystals is accomplished. The transmission of light increases up to 42–45% for nickel nanoparticles doped blue phase liquid crystal samples than pure blue phase liquid crystal with negligible residual birefringence. An increase in isotropic temperature was noticed in 40 nm nickel nanoparticles doped sample. Also an improvement in threshold voltage, induced birefringence, contrast ratio and Kerr constant with doping of nickel nanoparticles was observed. The present study is a synergistic correlation of size and concentration of nickel nanoparticles with blue phase liquid crystals and sufficiently productive for developing nanoparticles doped blue phase liquid crystal optical devices in future. • Size and concentration dependent magnetic nanoparticles stabilised blue phase liquid crystals are prepared and studied. • 7.8 °C wide BP range was observed using Ni NPs in BPLCs. • Variation in phase transition temperatures and BP range was noticed with variation in concentration and size of NPs. • An improvement in switching voltage, contrast ratio, birefringence and Kerr constant was observed by stabilization of BPLCs through Ni NPs.

Carbon Nanotubes Blended Nematic Liquid Crystal for Display and Electro-Optical Applications

In this paper, we investigate a commercial nematic liquid crystal (LC) mixture namely E7 dispersed with small concentrations of multi-walled carbon nanotubes (MWCNTs). The dielectric and electro-optical characterizations have been carried out in the homogeneously and vertically aligned LC cells. The electro-optical response of LC molecules has been enhanced by 60% after the addition of MWCNTs, which is attributed to the reduced rotational viscosity in the composites. MWCNTs act like barricades for ionic impurities by reducing them up to ∼34.3% within the dispersion limit of 0.05 wt%. The nematic–isotropic phase transition temperature (TNI) of the E7 LC has also been shifted towards the higher temperature, resulting in a more ordered nematic phase. The enhanced birefringence and orientational order parameter in the LC-MWCNTs are attributed to π-π electron stacking between the LC molecules and the MWCNTs. The outlined merits of the LC-MWCNTs composites evince their suitability for ultrafast nematic-based electro-optical devices.

P‐12.9: Dye‐Doped Nematic Liquid Crystal for Smart Windows

Dye‐doped nematic liquid crystal mixtures (DNLC) were prepared by mixing positive dichroic dye into our novel designed negative liquid crystals. Furthermore, the optical transmittance of their devices was investigated, with the concentration increasing of dichroic dye from 0.8wt% to 6.5wt%, the transmittance of both ON/OFF states decreases simultaneously and the contrast ratio goes up from 1.5 to 8.5 gradually. It is noted that when the dichroic dye is used at the concentration of 4.5wt% in DNLC, the dimming range is able to reach a high value up to 46.6%. Besides, owning to the low flow viscosity design of DNLC mixture, the devices are possible to be prepared easily by ODF process. For dimmer application, the low energy consumption is important and attractive, the DNLC with high dielectric constant makes the devices work at low voltage, the usable dimming can be driven even from 4V, besides the devices present low haze level. Moreover, the DNLC devices have fast response time under 200ms, and good low temperature storage properties at ‐ 40°C for 240hr. It is worth emphasizing here, there are two points of technology innovation for our reported DNLC devices. One is that the dimming range have an increase to 46.6% in comparison with 35−40% of our previous results. The other is that reliabilities are promoted because of the novel‐designed DNLC mixture. We expect our DNLC as smart windows could be applied in high‐speed train, automobile, airplane, buildings and so on in the close future widely.

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.

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.

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.

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.

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

Photonic NO2 Gas Sensing with Binaphthyl‐Based Dopants

AbstractA series of reactive binaphthyl‐diimine‐based dopants is prepared and investigated with respect to their potential for the chiral induction of structural coloration in nematic liquid crystal mixture E7 and the selective photonic sensing of nitrogen dioxide (NO2). Studies of the helical twisting power (HTP) in 4‐cyano‐4′‐pentylbiphenyl (5CB) reveal HTP values as high as 375 µm‐1 and the tremendous impact of structural compatibility and changes of the dihedral binaphthyl angle on the efficiency of the chiral transfer. Detailed investigation of the sensing capabilities of the systems reveals an extraordinarily high selectivity for NO2 and a response to concentrations as low as 100 ppm. The systems show a direct response to the analyte gas leading to a concentration‐dependent shift of the reflectance wavelength of up to several hundred nanometers. Incorporation of copper ions remarkably improves the sensor's properties in terms of sensitivity and selectivity, enabling the tailored tweaking of the system's properties.

Nanoparticle controlled nematic macroscopic properties

The impact of the weak disorder on systems exhibiting long-range order is of interest for all branches of condensed matter systems and is still relatively weakly explored. Experimentally adequate schemes for such purpose are homogenous mixtures of nematic liquid crystals (LCs) and appropriate nanoparticles (NPs), whose characteristic linear size R ranges between nm and several micrometers. In such systems, NPs in most cases impose a random field-type of disorder due to local NP-induced symmetry breaking. The resulting disorder strength can be fine-tuned by varying several parameters: kind of NPs (conducting, semiconducting, non-conducting), their geometry, R, distribution of R values, NPs’ surface treatment. Furthermore, the resulting NP-LC configurations could be exploited for several applications, in particular in the realm of light-manipulation devices. We carried out a numerical study, where we explore systematically the impact of a relatively weak NP-induced disorder on nematic macroscopic LC order. The semi microscopic Lebwohl-Lasher-type model was used, where different control parameters were varied (concentration and partial orientational order of NPs, LCNP interaction strength, temperature). Research outcomes could be useful mostly for applications based on disorder-controlled tunable LC optical properties.

Dielectric and electrooptical properties of hockey-stick-shaped liquid crystal with a negative dielectric anisotropy

We investigated dielectric properties of a hockey-stick-shaped liquid crystal (HLC). Two dielectric relaxation modes were observed at 0.91 kHz and 4.51 MHz. The low frequency relaxation modes in isotropic, smectic, and nematic phases are related to the motion of ions, collective tilt fluctuation, and rotation around the long molecular axis, respectively. Meanwhile, the high frequency relaxation modes in nematic and smectic phases was due to the rotation around the short axis of the molecules and hindered by the resistance of the ITO layers. We also examined the electrooptical response of the 5.0 wt% HLC-doped commercial nematic liquid crystal (LC) mixtures. The birefringence of the LC mixture was slightly increased, while the falling time and the rotational viscosity was decreased in the nematic phase.

Chemical-Physical Characterization of a Binary Mixture of a Twist Bend Nematic Liquid Crystal with a Smectogen

Nematic twist-bend phases (NTB) are new types of nematic liquid crystalline phases with attractive properties for future electro-optic applications. However, most of these states are monotropic or are stable only in a narrow high temperature range. They are often destabilized under moderate cooling, and only a few single compounds have shown to give room temperature NTB phases. Mixtures of twist-bend nematic liquid crystals with simple nematogens have shown to strongly lower the nematic to NTB phase transition temperature. Here, we examined the behaviour of new types of mixtures with the dimeric liquid crystal [4′,4′-(heptane-1,7-diyl)bis(([1′,1″-biphenyl]4″-carbo-nitrile))] (CB7CB). This now well-known twist-bend nematic liquid crystal presents a nematic twist-bend phase below T ≈ 104 °C. Mixtures with other monomeric alkyl or alkoxy -biphenylcarbonitriles liquid crystals that display a smectic A (SmA) phase also strongly reduce this temperature. The most interesting smectogen is 4′-Octyl-4-biphenylcarbonitrile (8CB), for which a long-term metastable NTB phase is found at room and lower temperatures. This paper presents the complete phase diagram of the corresponding binary system and a detailed investigation of its thermal, optical, dielectric, and elastic properties.